Home

The Microcontroller Idea Book: Circuits, Programs & Applications

Contents

1. DS1225 DS1213B C NC l VCC l VCC Al2 2 WE 2 A7 3 NC 3 VCC DS1213B A6 4 A8 4 ONLY A5 5 AQ 5 A4 6 All 6 A3 7 OE 7 A2 8 A1Q 8 Al 9 CE 9 CE AQ DQ7 DOO l DO6 l DOI DOS l DQ2 DQ4 l GND DOS GND l 8Kx8 NVRAM SMARTSOCKET ACCEPTS 6264 8K X 8 SRAM Figure 4 1 Pinouts for Dallas Semiconductors 8K NVRAM and SmartSocket space even though it may contain NVRAM EEPROM or EPROM and call the memory beginning at 0 up to 7FFFh or the top of RAM the RAM space BASIC 52 s programming commands are designed to meet the requirements for EPROMs using either of two programming algorithms or procedures You can use the same commands to store programs in NVRAM or EEPROM Like EPROMS these devices provide nonvola tile storage in other words their contents don t disappear when power is removed Plus they have two advantages over EPROMs they don t need any special programming voltages and they don t need ultraviolet exposure to erase This makes them much more convenient to use For these reasons the first circuit we ll look at offers a choice of NVRAM or EEPROM for nonvolatile storage Later we ll add circuits that allow you to program EPROMs for those who want this option NVRAM Dallas Semiconductor offers NVRAM chips that you can use for nonvolatile storage These work e
2. TELCOM TC7211A 4 DIGIT 4 DIGIT DISPLAY 7 SEGMEN 82 C 55 DECODER DRIVER LCD MODULE PAO 271397 4 PALL TS 2815 DATA bs b PA 2 29 B2 IN rel c eA 30 53 42 c DIGIT i 3 2 SEGMENTS e 4 e PA 4 slip in PASTS SDZ piGIt 3 37 PASIS S303 SELECT 6 PA 7 Sp 4 _ 17 i bE b USE ANY fo DIGIT 2 veel SEGMENTS PORT TO el e CONTROL f i f TC7211A g gi a 3 a r b b eee i 6 i DIGIT 3 7 SEGMENTS e 9 e he f D g g a 20 a 21 Bleg bs cak C Cc To C DIGIT 4 24 lt SEGMENTS 26 gt BACK PLANE hes f g g BACK PLANE i J f j f Figure 8 7 With the TC7211A decoder driver you can control a 4 digit display with 8 port bits The Microcontroller Idea Book 137 Chapter 8 1 Write the number you want to display to data inputs BO B3 and bring a digit select input D1 D4 high to select the digit to write to You can use the same XBY statement to do both For example to write 7 to digit 2 use this statement XBY port address 27H 2 With the data still on B0 B3 bring the digit select input low The data must remain on BO B3 for at least 200 nanoseconds after the digit select input goes low For step 1 s example you would write XBY port address 07H Follow the same procedure for each digit and the TC7211 will continue to drive the appropriate segments on all four digits To change t
3. ne OOK OFFSET ADJUST BUFFER LEVEL SHIFTER AMPLIFIER ATTENUATOR EXAMPLE USE 12V f 5y VIN vouT OV 12V Figure 9 9 With this circuit you can adjust the level and amplitude of an analog signal so that it varies from O to 5V As an example of how to use the circuit if VIN varies from 12V to 12V adjust R4 for a 2 5 volt swing at VOUT then adjust R5 to raise VOUT to achieve the desired 0 to 5V swing Resistor R4 can increase the gain as well as decrease it If you need to shift the signal level down instead of up connect R5 to 15V instead of 15V If you don t need level shifting you can remove R5 and connect pin 6 only to R1 and R2 168 The Microcontroller Idea Book Using Sensors to Detect and Measure Choosing a Converter The ADC0848 is a good general purpose chip but you may want to look at other converters depending on your application Below are some things to consider when choosing an A D converter Example answers describe the ADC0848 using information from its data sheet e What is the analog input range OV to V e How many analog channels are there 8 e What is the converter s resolution 8 bits e How fast is the conversion 30 microseconds typical 60 microseceonds maximum e How accurate is the conversion 1 LSB least significant bit 1 2 LSB version available e What are the power supply requirements and power consumption 4
4. Ce ing rom Aja lal ca CC ail mas alo e d c c COMMON CATHODE COMMON ANODE Figure 8 3 A 7 segment display can show numbers from 0 to 9 plus hex digits A F In a common cathode LED display all of the cathodes connect together while in a common anode display all of the anodes connect The displays come in two types common anode or common cathode In a common anode display the anodes of each segment connect internally To use the display you connect the anodes to a voltage source and turn on individual segments by grounding them through a current limiting resistor A common cathode display is the opposite the cathodes connect internally so you ground the cathodes and apply voltages through current limiting resistors at the segments you want to light Deciphering pinouts Unfortunately there isn t much standardization for pinouts of 7 segment displays If you don t know the pinout for a display you can find it by experimenting You Il need a 330 ohm resistor and a 5 volt supply Sometimes you ll find CC or CA stamped on the package to indicate common cathode or common anode If even this information is lacking begin by connecting one lead of the 130 The Microcontroller Idea Book Displays
5. x xX xX DON T BIT SET ZRESEI I CARE l SET RESET LT SELECT Sel S S S z y BIT SET RESET ACTIVE Figure 6 8 With bit 7 0 writing to the 8255 s control register will set or clear individual bits in Port C Bit Control Another useful feature of the 8255 is the ability to set and clear individual bits on Port C You do so again by writing to the control register as Figure 6 8 shows Bit 7 must be 0 Bit 0 selects set or reset clear for the bit and bits 1 3 select the bit to set or clear For example this BASIC 52 statement sets bit 7 of Port C XBY OFCO3h OFh To clear bit 7 use this statement XBY OFCO3h 0Eh 106 The Microcontroller Idea Book Inputs and Outputs To set or clear a different bit determine which bits to set and clear for the result you want convert the value to decimal or hexadecimal and write the value to OFCO3h Adding Handshaking For many applications Mode 0 is all you need Modes 1 and 2 add handshaking or control signals for components that require them Mode 1 is Strobed Input Output It uses Port C for handshaking signals that let the 8052 BASIC and the peripheral tell each other whether or not they re ready to send or receive data and to confirm that data has been received Mode also latches the input data so you can use an external signal
6. 4511B BC D TO 7 SEGMEN 82 C 55 5V LATCH DECODER DRIVER 3l Ape a 1S x aN le Hei by 2 150 bN d j i 3 1 159 ae PA z A 5 Pa Lig sasaa PA 275 Ac d A PA 3 D 9 50 e x e 15 150 f USE ANY PORT f N d OUTPUTS TO S 14 150 CONTROL A D g Iy R a DIGIT D C BA DISPLAYED 2000 Q f b 2200 20120 2 E g E O 3 2100 4 2101 5 a A 21120 6 1 11 7 d 188 8 1 9 COMMON CATHO DE 7 SEGMENT L D Figure 8 4 Four output port pins can control a 7 segment LED resistor to ground on your power supply Clip the resistor s other end to one of the LED s pins Use a test lead to touch the power supply s 5V output to each of the other pins in turn If only one or two connections cause a segment to light you have a common anode display and the common anode is the pin or pins that connect to 5V when the segment lights There The Microcontroller Idea Book 131 Chapter 8 Listing 8 2 Causes a 7 segment LED to display each digit in sequence 10 REM configure all ports as outputs 20 XBY OFC0O3H 80H 30 REM write each value to the display in sequence 40 FOR I 0 TO 9 50 XBY OFCOOH I 60 REM delay after each write 70 FOR J 1 TO 500 NEXT J 80 NEXT I 90 END may be two common anode pins To find the pin that controls each segment leave the 5 V lead on a common anode pin and connect the resistor to each pin in turn noting the results For a common cath
7. 45438 V LCD DECODER DRIVER SEGMENTS Ling 9 m a Ale a a Se EC 82 C 55 bH 5 mel i 4 PAO SA ed f E es TAS ig 5 P dH a PA 2 C 4 eH 3 eed e C PA 3 4D HF F 6l ph j 7 SEGMENT LCD g g T may DIGIT DC B A DISPLAYED USE ANY PORT d47x x 18 oe A OUTPUTS TO RST V 200 l CONTROL A D a 22120 2 1 2 lpi 2211 3 7 out 2102 4 THRESH 1QQHZ 9101 5 L SND LCD DRIVE Or a 6 Ia A VOLTAGE ll 4 O luF 12220 8 I 102 9 Figure 8 6 A 4543B driver can control a 7 segment LCD A 555 timer controls the drive voltage As in Figure 8 4 you control the display by writing to inputs A D If the display contains other types of segments such as or a leading you can control these as well For example for a leading 1 connect digit 1 s two segments to pins 10 and 11 on the 4543 When you write to the data inputs the appropriate segments will light Multi digit driver As with the LEDs there are driver chips for multi digit LCD modules Figure 8 7 shows Telcom Semiconductor s formerly Teldyne TC7211A which will drive four 7 segment LCDs and includes an on chip oscillator and backplane driver To display a number using Figure 8 7 s circuit follow these steps 136 The Microcontroller Idea Book Displays
8. LECTROLYTIC CAPACITORS Figure 3 4 How to determine the correct orientation for ICs diodes LEDs and electrolytic capacitors 32 The Microcontroller Idea Book Powering Up Construction Tips These are some things to be aware of as you build the circuit e Choose a circuit board that has room for additions at least 4 by 6 inches e A board with interleaved buses such as Vector s 3677 series allows easy low impedance connections to 5V and ground Designate one bus as ground and the other as 5V For power and ground connections wrap one end of the wire to the appropriate pin on the chip and trim and solder the other end directly to the bus e To connect the power and ground buses to the 5V supply use thick AWG 22 or lower wires not 30 wire wrap wires You can solder the other ends of the wires to banana plugs or screw terminals or clip your power supply leads directly to the wires e The schematic doesn t show an ON OFF switch for the circuit but you can add a SPST toggle or slide switch in series with the connection to the 5V supply if you wish e Place C8 near where the 5V supply connects to the board Mount decoupling capacitors C9 C13 so that each chip s 5V and GND pins are near a capacitor In other words space the capacitors evenly around the board don t group them all in one area Keep the wires or traces between the capacitor s leads and the IC s 5V and ground pins as short as possib
9. X 340 GOSUB 3000 350 XBY WT 6 X 360 INPUT 24 hr 0 or 12 hr 1 clock TT 370 IF TT 0 THEN GOSUB 3000 ELSE GOSUB 600 380 INPUT minutes 0 59 X 390 GOSUB 3000 400 XBY WT 2 X 410 INPUT seconds 0 59 X 420 GOSUB 3000 430 XBY WT 1 X 440 XBY WT 0 The Microcontroller Idea Book 18 Chapter 10 Listing 10 3 page 2 of 4 450 PRINT Press any key when ready to start the clock 460 A GET IF A 0 THEN GOTO 460 470 XBY WT 9 XBY WT 9 AND 7FH 480 RETURN 500 INPUT hour 0 23 X 510 GOSUB 3000 520 XBY WT 4 X 530 RETURN 590 REM set up 12 hour clock 600 INPUT hour 1 12 X 610 INPUT AM 0 or PM 1 AP 620 GOSUB 3000 630 XBY WT 4 X AP 20H TT 40H 640 RETURN 1000 REM display current time and date 1010 REM clear TE for error free reads 1020 XBY WT 0BH XBY WT 0BH OR 80H 1030 REM get hours 1040 X XBY WT 4 AND 1FH 1050 GOSUB 3100 1060 PRINT Time X 1070 REM get minutes 1080 X XBY WT 2 1090 GOSUB 3100 1100 PRINT X 1110 REM get seconds 1120 X XBY WT 1 1130 GOSUB 3100 1140 PRINT X 1150 IF TT 0 THEN 1220 1160 IF AP 1 THEN 1190 1170 PRINT am 1180 GOTO 1220 1190 PRINT pm 1200 PRINT 182 The Microcontroller Idea Book Clocks and Calendars Listing 10 3 page 3 of 4 1210 REM get month 1220 X XBY WT 9 AND 3FH 1230 GOSUB 3100 1240 PRINT Date X 1250 REM get day
10. _ a 80 BIT 7 _ U14 20 10 e HE OUTPUT LATCH Figure 6 2 Circuits for adding inputs and outputs to the 8052 BASIC system The Microcontroller Idea Book 90 Inputs and Outputs U11 is a 74HCT138 3 to 8 line decoder that generates individual chip enable signals for eight 1K blocks in the memory area from E000h to FFFFh It works the same way that U6 generates chip selects for 8K blocks in the main circuit U11 is enabled whenever pin 7 of U6 is low which occurs when the 8052 BASIC reads or writes to addresses from E000h to FFFFh Address lines A10 A11 and A12 determine which of U11 s outputs goes low when the chip is enabled As with U6 each output is low for a different memory area For example pin 15 is low only when addresses from E000h to E3FFh are being read or written to One possible point of confusion is that both pin 7 of U6 in Figure 3 1 and pin 15 of U11 are chip selects with a starting address of E000h One controls memory accesses in the entire 8K block from E000h to FFFFh while the other controls only the 1K block from E000h to E3FFh To distinguish the two I ve labeled U11 s pin 15 as EOOOH 1K U12 and U14 are examples of input and output ports that U11 can enable An Input Port U12 is a 74LS244 octal buffer that adds eight inputs to the circuit The buffer s Y outputs connect to the system s data bus D0 D7 The chip has two groups of four buffers with each having its
11. expression gt expression C R Greater than test relational operator expression lt expression C R Less than or equal test relational operator expression gt expression C R Greater than or equal test relational operator Same as PRINT ABS expression C R Returns the absolute value of expression expression AND expression C R Logical AND ASC character C R Returns the value of ASCH character ATN expression C R Returns the arctangent of expression BAUD expression C R Sets the baud rate for LPT pin 8 For proper operation XTAL must match the system s crystal frequency CALL integer C R Calls an assembly language routine at the specified address in program memory The Microcontroller Idea Book 75 Chapter 5 CBY expression C R Retrieves the value at expression in program or code memory CHR expression C R Converts expression to its ASCII character CLEAR C R Sets all variables to 0 resets all stacks and interrupts evoked by BASIC CLEARI CR Clears all interrupts evoked by BASIC Disables ONTIME ONEX1 CLEARS C R Resets BASIC 52 s stacks Sets control stack OFEh argument stack 1FEh in ternal stack value in 3Eh in internal RAM CLOCKO C R Disables the real time clock CLOCK1 C R Enables the real time clock CONT C Continues executing program after STOP or CONTROL C COS expression C R Returns the cosine of expression CR PRINT option Causes a carriage re
12. 22a 5 WRITE SSaWR cHaP 5V DATA BUS coon cus O DO D7 7 CH6 H INTR sgl cHe D BO MA DBI MAI DB2 MA2 eo DB3 MA3 Set osr a 2 1uF_ lyr DB4 MA4 T a ae DBS AGND gt D B6 12 i DGND T MA4 MAS MODE SINGLE ENDED PSEUDO XxX DIFFERENTIAI l l DIFFERENTIAI xX DON T CARE S CT CHANNEL AT MAQ Q MA2 Figure 9 4 The ADC0848 interfaces easily to an 8052 BASIC system and can measure up to eight analog inputs Figure 9 4 shows an ADC0848 interfaced to Chapter 3 s 8052 BASIC system The connec tions are similar to those used for RAM WRITE and READ drive the converter s WR and RD inputs The converter is shown addressed at COOOh but you can use any unused chip select The Microcontroller Idea Book 159 Chapter 9 line Digital outputs DBO DB7 connect to the data bus D0 D7 DBO DB4 also function as control inputs MAO MA4 Up to eight analog inputs can connect to pins 2 9 on the ADC0848 The voltage at VREF determines the converter s full scale voltage which is the input that results in an output of 11111111 or FFh For maximum range connect VREF to the 5V supply or to a more precise 5 volt reference like an LM336 5 0 reference diode The analog inputs can then range from 0 to 5 volts Adjusting the Range If your sensor s output is much less than 5 volts you can increase the resolution of the
13. Chapter 5 BASIC 52 Keywords by Function The following is a quick reference to BASIC 52 s keywords grouped by function After this is a more detailed list arranged alphabetically with the syntax and a brief description of what each keyword does Some of the keywords like RUN LIST and PRINT are ones that you ll use constantly A few like NULL or UIO have specialized uses that you may never need Again for a more complete reference see the BASIC 52 programming manual Running and Listing Programs CONT LIST NEW RAM REM ROM RROM RUN STOP XFER Storing Programs in NV Memory F PROG FPROG1 FPROG6 PGM PROG PROG1 PROG6 Program Control Structures loops and subroutines DO UNTIL DO WHILE END FOR TO STEP NEXT GOSUB GOTO IF THEN ELSE ON GOSUB ON GOTO RETURN 72 Printing and Displaying Information on the Host Computer PHO PH1 PRINT P Additional PRINT Formatting CR SPC TAB USING U Input Output CBY DBY GET INPUT LIST NULL PORT1 PHO PH1 PRINT P XBY System Control Values BAUD FREE LEN MTOP STRING The Microcontroller Idea Book Programming Math Operators Data Storage ASC CHR CLEAR CLEARS DATA DIM LD lt POP lt gt PUSH gt READ lt RESTORE ABS ST ATN COS Timers and Interrupts EXP INT CLEARI LET CLOCKO LOG CLOCK1 NOT IDLE PI IE RND IP SGN ONERR SIN ONEX1 SQR ONTIME T
14. Logic I 3 5V or greater or Open no connection Figure 12 3 shows the transmissions that result for each of these states ENCODER OSCILLATOR PIN 12 ENCODED ONE ENCODED ZERO ENCODED OPEN DATA PULSE PERIOD lt 7 DATA BIT PERIOD lt gt Figure 12 3 Pulse patterns at pata out of the MC145026 encoder 202 Tne Microcontroller Idea Book Wireless Links Because there are three possible states the information is trinary as opposed to binary with just two states With five address inputs and three possible states for each you can have as many as 243 receivers each with its own address Although data inputs D6 D9 also transmit in trinary form the receiver decodes open inputs as logic 1 s so in effect the data bits are binary For testing you can use jumpers or switches to 5V or ground or leave the pins open to set the data and address inputs Transmit Enable TE has an internal pullup which turns off the transmitter when pin 14 is not connected To enable transmitting TE must pulse low for at least 65 nanoseconds For manual operation you can use a jumper or switch S1 to bring TE low Components R1 R2 and C2 set the frequency of the on chip oscillator This in turn controls the width of the transmitted pulses The figure shows the data sheet s formula
15. RS232 interface power supply monitor ICs BASIC 52 programming environment enhanced BASIC 52 8051 assembler BASIC 52 systems The Microcontroller Idea Book Micro Future 40944 Cascado Place Fremont CA 94539 510 657 0264 Micromint 4 Park Street Vernon CT 06066 203 871 6170 Midwest Micro tek 2308 E 6th St Brookings SD 57006 605 697 8521 Mitel Semiconductor P O Box 13089 Kanata Ontario K2K 1X3 Canada 1 800 267 6244 613 592 2122 National Semiconductor Corporation 2900 Semiconductor Drive P O Box 58090 Santa Clara CA 95052 8090 408 721 5000 1 800 272 9959 Newark Electronics 4801 N Ravenswood Ave Chicago IL 60640 4496 312 784 5100 Omega Engineering One Omega Drive Box 4047 Stamford CT 06907 1 800 826 6342 The Microcontroller Idea Book Sources BASIC 52 programming environment 80C52 BASIC chip systems related products 8052 Basic boards switch matrix chips linear digital ICs electronic components sensors 259 Appendix A Optek Technology 1215 West Crosby Rd Carrollton TX 75006 214 323 2200 Philips Components Signetics 811 East Arques Ave P O Box 3409 Sunnyvale CA 94088 408 991 2000 Photronics Research 109 Camille St Amite LA 70422 504 748 7090 Prologic P O Box 19026 Baltimore MD 21204 410 661 5950 PseudoCorp 716 Thimble Shoals Blvd Suite E Newport News VA 23606 804 873 1947 Rigel Corporation P O Box 90040 Gainesv
16. The Microcontroller Idea Book 133 Chapter 8 Listing 8 3 Controls eight 7 segment LEDs with ICM7218 driver 10 REM address of 8255 Port A 20 A 0FC0O0H 30 REM address of 8255 control word 40 X A 3 50 REM set 8255 for all outputs 60 XBY X 80H 70 REM set WR 80 XBY X 9 90 REM write to each digit 100 FOR M 0 TO 7 110 REM step through all numbers at each digit 120 FOR I 0 TO 8 130 REM add 10h to turn off decimal point 140 D 1 10H M 20H 150 GOSUB 500 160 REM delay to display each digit 170 K 500 180 FOR J 1 TO K NEXT J 190 NEXT I 200 NEXT M 210 END 490 REM write data to port A and toggle W PC 4 500 XBY A D 510 XBY X 8H 520 XBY X 9 530 RETURN range for peak current for most LEDs and the 2 5 milliampere average current causes the displays to appear brighter than you might expect With all digits displaying 8 s this circuit draws 140 milliamperes so be sure your power supply can handle it To write a value to the display you select the digit with data address inputs DAO DA2 write the data to inputs IDO ID7 and strobe WRITE low The WRITE pulse must be at least 400 nanoseconds wide and IDO ID7 must remain valid for at least 125 nanoseconds after WRITE goes high BASIC 52 is slow enough to meet these requirements using XBY statements to write to the port that controls the 7218C Pin 9 allows you to select one of three modes which determine what digits the displays show In Code B mode yo
17. bulletin boards which are good sources for files relating to the 8051 2 including the 8052 BASIC BBS Name Phone Number Available Files Circuit Cellar 203 871 1988 8052 programming tools programs Intel Applications 503 264 7999 BASIC 52 source code Philips Semiconductor 1 800 451 6644 BASIC 52 source code Systronix 801 487 2778 HEX2RAM BAS HEXLOAD BAS Internet Many of the vendors listed here now have information available on the World Wide Web Lakeview Research s Web site includes a BASIC 52 page with links to product vendors and updates to the information in this book You can also save yourself some typing by downloading a file containing all of the code listings in the book You can find Lakeview Research on the Internet at http www lvr com 254 The Microcontroller Idea Book Product Vendors Sources The following companies offer products related to microcontroller applications Many are mentioned as sources for particular products in this book Airpax Company 604 West Johnson Avenue P O Box 590 Chesire CT 06410 203 271 6000 Allegro Microsystems 115 Northeast Cutoff Box 15036 Worcester MA 01615 508 853 5000 All Electronics Corp P O Box 567 Van Nuys CA 91408 0567 1 800 826 5432 Allen Systems 2346 Brandon Road Columbus OH 43221 614 488 7122 Anywhere Engineering 920 Eighth Street Boulder CO 80302 303 442 0556 Amperex Philips Sales Corporation Providence Pike Slatersville RI 02
18. 10H A AND 20H 20H A AND 40H 40H A AND 80H 80H NN U PWN EP ll 96 The Microcontroller Idea Book Inputs and Outputs Listing 6 2 Sets or clears a bit at output port E400h 5 REM variable A contains the last data written to 0E400h 10 INPUT Enter a bit to set or clear 0 7 X 20 INPUT Enter 1 to set 0 to clear Y 30 IF Y 1 THEN A A OR 2 xX 40 IF Y 0 THEN A A AND OFFH 2 xX 50 XBY OE400H A 60 END Listing 6 1 is a program that reads the buffer and displays the value of each bit The program is similar to Listing 3 1 which displays the bit values at Port 1 Line 20 finds the logic state of bit 0 by logically ANDing the byte with a mask byte that is all 0 s except for bit 0 00000001 The result is 1 if bit 0 is 1 and 0 if bit 0 is 0 Lines 30 90 are similar except that each time a different bit in the mask byte is 1 In each case the program divides the result by 2 raised to the power of the bit number Since 2 0 equals 1 line 20 leaves out this step Each PRINT statement shows the logic state of one of the bits At the output port if you want to change just one bit in the byte you have to know the current value of the byte The simplest way to accomplish this is to save the last value you wrote Or you could wire an input buffer at the same address with each input bit connecting to the corresponding output bit and read the input when you need to know the current value Listing 6 2 p
19. 40 PRINT Bit 2 PORT1 AND 4 4 List Program from 8052 50 PRINT Bit 3 PORT1 AND 8 8 60 PRINT Bit 4 PORT1 AND 10H List and File Program from 8052 70 PRINT Bit 5 CPORT1 AND 20H 80 PRINT Bit 6 CPORT1 AND 40H Save all Data to a Data File 90 PRINT Bit 7 PORT1 AND 80H 100 END Send an ASCII Hex File to RAM Load Text Editor Execute an MS DOS Command ENTER to select ESC to quit CSB Exit Jl Help Edit E Menu YF CirScr E Dir JF LastLn 9g ChoBoud Gy EdLn Figure 15 1 MDL Labs Basikit includes communications and program editing abilities The Microcontroller Idea Book 247 Chapter 15 e Elimination of the need to use line numbers at all e Automatic stripping of comments to save memory and execution time in uploaded programs e On line help for BASIC 52 e Debugging tools such as setting of breakpoints or watch variables for program testing e Conversion of BASIC 52 programs to hex files for EPROM programming e Screening of variable names for duplicates or embedded keywords Pc Boards If you d rather not build your own 8052 BASIC system from scratch a variety of sources are ready to help here as well with fabricated pc boards ready for use with the 8052 BASIC chip The boards contain all of the components required to get an 8052 BASIC system up and running Most come with complete schematics to make it easy to add to the included circuits A few boards a
20. Error messages and program termination PRINT CR Line LINE Character I unexpected GOTO 600 PRINT CR Line LINE Unknown record type CH GOTO 600 PRINT CR Line LINE Checksum failure Expected PHO ABS CHECK CH GOTO 600 PRINT CR Line LINE Verify error at address PHO ADDR PHO The byte at addr is CBY ADDR PHO The byte should be CH GOTO 600 PRINT Stop sending input file Type a CONTROL C to quit GOTO 605 Normal program exit point PRINT CR Received an End record in line LINE Convert the ASCII text to numbers C ASC 0 I CH HI C C ASC 0 I 1 CH LOW C RETURN The Microcontroller Idea Book END CH 265 Appendix B Listing B 2 page 1 of 4 HEXLOAD BAS copies an Intel Hex file into RAM EEPROM or EPROM in an 8052 BASIC system 1 STRING 82 80 2 PRINT TAB 22 HEX FILE LOADING PROGRAM 1 2 3 PRINT TAB 14 C 1990 1991 Systronix Inc All rights reserved PRINT 4 PRINT This program accepts as input an Intel format hex file and stores 5 PRINT it in RAM EPROM or EEPROM at the addresses speci fied PRINT 6 PRINT PRINT Select the destination device type PRINT 7 PRINT TAB 10 1 RAM PRINT TAB 10 2 Timed EEPROM 8 PRINT TAB 10 3 EPROM Intelligent algorithm 9 PRINT TAB 10 4 EPROM 50mS algo
21. If you do so leave the unused inputs open Using the Programming Commands When Figure 4 3 s circuit is added you re ready to power up and try the programming commands Begin by entering any simple BASIC 52 program such as one of the examples in Chapter 3 Setting MTOP If you have a 32K RAM at U7 you have an additional step to perform before you store a program in U8 On bootup BASIC 52 tests contiguous memory and sets MTOP to the highest value it finds below E000h But BASIC 52 s programming commands won t work unless MTOP is below 8000h To enable program storage type the following command MTOP 7FFFh This ensures that BASIC 52 won t try to store RAM programs variables or strings in the area that you ve reserved for permanent program storage although it doesn t prevent you from writing to the area with BASIC 52 s XBY operator If U7 is an 8K device MTOP is 1 FFFh well below 8000h so you don t have to worry about changing it Saving a Program To copy the current program from U7 to U8 type F PROG The screen will display the number 1 indicating that this is the first BASIC 52 program to be stored in the device and after a short delay the READY prompt should return PROG is an alternate command that uses a slower programming algorithm and should also work The Microcontroller Idea Book 53 Chapter 4 If BASIC 52 is unable to program the chip you ll see this ERROR PROGRAMMING If you get this
22. ON X GOSUB 800 300 Transfers program control to a subroutine at line 800 position 0 in the list ON expression GOTO line number line number line number R Transfers program control to one of the line numbers in a list of numbers The value of expression matches the position of the line number selected with the first line number at position 0 Example X 0 ON X GOTO 800 300 Transfers program control to line 800 position 0 in the list The Microcontroller Idea Book 79 Chapter 5 ONERR line number R Passes control to line number following an arithmetic error Arithmetic errors in clude ARITH OVERFLOW ARITH UNDERFLOW DIVIDE BY ZERO and BAD ARGUMENT ONEX1 line number R On interrupt 1 pin 13 BASIC 52 finishes executing the current statement and then passes control to an interrupt routine beginning at line number The interrupt routine must end with RETI ONTIME number of seconds line number R When TIME number of seconds BASIC 52 passes control to an interrupt rou tine beginning at line number The interrupt routine must end with RETI CLOCK1 starts the timer expression OR expression C R Logical OR P same as PRINT PCON C R Retrieves or assigns a value to the 8052 s special function register PCON PGM CR Programs an EPROM EEPROM or NV RAM with data from memory The fol lowing data must be stored in internal data memory in the locations listed 1Bh 19h High byte low byte of first addr
23. Parts list for Figure 4 5 Semiconductors D2 D3 1N270 or similar germanium diode Q1 Q2 PN2907 or similar PNP general purpose transistor U10 75453 dual peripheral OR driver Resistors 1 4 watt 5 tolerance R11 R14 4 700 ohm R12 R13 10 000 ohm R15 R16 10 000 ohm Capacitors 16WVDC 20 tolerance C15 0 1 microfarad ceramic disc Miscellaneous J5 J6 SIP header 3 terminal and shorting block When BASIC 52 executes a programming command PGM EN goes low pin 3 of U10 goes low and Q1 switches on This brings VPP to 12 5 volts Diode D2 prevents current from flowing into the 5V supply When programming is finished PGM EN goes high again and VPP returns to 4 7V Resistor R10 limits U1OA s output current and R11 ensures that pin 3 of U10 pulls up to 12 5V Capacitor C14 provides power supply decoupling If you happen to have an older 21V EPROM the circuit should also work with a 21V supply in place of 12 5V FPROG Circuits If you want to use the FPROG commands for faster EPROM programming additional circuits are required These are identical to the circuits that switch VPP except that they instead switch VCC to 6V during programming With the FPROG circuits shown in Figure 4 5 during normal non programming operation VCC is actually slightly less than 5V due to D3 s voltage drop This should cause no 60 The Microcontroller Idea Book Saving Programs problems with EPROMSs that have a 10 percent power supp
24. and even floating point math for handling Tne Microcontroller Idea Book 13 Chapter 2 fractional quantities But there are some primitive aspects to the language For example the on line editing functions are limited Once you write a program line you can change it only by retyping from the beginning The limitations are understandable because the entire programming language has to fit in the 8052 s 8 kilobytes of ROM Fancy editing and other features just aren t feasible in this small space There are solutions here as well You can get around many of the editing limitations by writing and editing programs off line using your personal computer and text editor and then uploading to the 8052 BASIC system And there are software and hardware products that enhance BASIC 52 and make it easier to use especially for longer more complex programming jobs What You Need To use the 8052 BASIC chip you need the following equipment materials and skills Components The 8052 BASIC chip and supporting components are widely available Appendix A lists sources for the components used in the circuits described in this book Power Supply You ll need a regulated 5 volt power supply to power the circuits Output capability of at least 500 milliamperes is recommended for general experimenting The power supply can be powered by batteries or AC line voltage but it must have a regulated output between 4 75 and 5 25 volts Construction Ma
25. calculates or displays information is a candidate for putting a microcon troller inside The largest single use for microcontrollers is in automobiles just about every car manufactured today includes at least one microcontroller for engine control and often more to control additional systems in the car In desktop computers you can find microcon trollers inside keyboards modems printers and other peripherals In test equipment microcontrollers make it easy to add features such as the ability to store measurements to create and store user routines and to display messages and waveforms Consumer products that use microcontrollers include cameras video recorders compact disk players and ovens And these are just a few examples Tne Microcontroller Idea Book Chapter 1 A microcontroller is similar to the microprocessor inside a personal computer Examples of microprocessors include Intel s 8086 Motorola s 68000 and Zilog s Z80 Both microproc essors and microcontrollers contain a central processing unit or CPU The CPU executes instructions that perform the basic logic math and data moving functions of a computer To make a complete computer a microprocessor requires memory for storing data and programs and input output I O interfaces for connecting external devices like keyboards and displays In contrast a microcontroller is a single chip computer because it contains memory and I O interfaces in addition to the CPU
26. converter by connecting VREF to a voltage slightly larger than the highest voltage you expect to measure To illustrate consider a sensor whose output ranges from 0 to 0 5 volt The 8 bit digital output of the converter represents a number from 0 to 255 If VREF is 5 volts each count equals 5 255 or 19 6 millivolts A 0 2 volt analog input results in a count of 10 while a 0 5 volt input results in a count of 26 If your input goes no higher than 0 5 volt your count will never go higher than 26 and the measured values will be accurate only to within 20 millivolts or 1 255 of full scale But if you adjust VREF down to 0 5 volts each count now equals 0 5 255 or 2 millivolts A 0 2 volt input gives a count of 102 a 0 5 volt input gives a count of 255 and the measured values can be accurate to within 2 millivolts However if you decrease VREF as described above you also increase the converter s sensitivity to noise With VREF at 5 volts a 20 millivolt noise spike will cause at most a 1 bit error in the output If you decrease VREF to 0 5 volt the same spike can cause an error of 10 bits since each bit now represents 2 millivolts not 20 Minimizing Noise The rapid switching of digital circuits can cause voltage spikes in the ground lines and these can cause errors in analog measurements Good routing of ground wires or pc board traces can minimize noise in circuits that mix analog and digital circuits To minimize noise provide
27. into the enclosure For a more finished appearance you can buy bezels with matching sheets of clear or tinted plastic to cover the displays and mounting hole Most character based LCD modules have a mounting hole in each corner of the circuit board You ll need to drill matching holes in the enclosure and cut a hole for the display to show through Some displays have a ribbon cable attached others have 14 holes on 0 1 centers to which you can solder a ribbon cable or a header into which a cable plugs Be sure to mount your displays so they will be visible from the expected viewing angle If necessary tilt the display slightly in its mounting 152 The Microcontroller Idea Book Using Sensors to Detect and Measure 9 Using Sensors to Detect and Measure With your 8052 BASIC system and some sensors you can detect and measure properties such as temperature light chemical composition motion and more This chapter focuses on how to use sensors in an 8052 BASIC or other microcontroller system Sensor Basics A sensor is a device that responds to a physical property or condition Other terms for sensor are detector and transducer Sensors enable a circuit to learn about the world outside of itself much as humans use the senses of sight hearing touch smell and taste A sensor may respond in any of a number of ways For example litmus paper is a sensor that responds to acidity by changing color For interfacing to the 8052 BASIC
28. turns to O until a new character arrives GOSUB line number R Causes BASIC 52 to transfer program control to a subroutine beginning at line number ARETURN statement returns control to the line number following the GOSUB statement GOTO line number C R Causes BASIC 52 to jump to line number in the current program IDLE R Forces BASIC 52 to wait for ONTIME or ONEX1 interrupt The Microcontroller Idea Book 77 Chapter 5 IE C R Retrieves or assigns a value to the 8052 s special function register IE IF relational expression R THEN program statements ELSE program statements If relational expression is true executes program statements following THEN If relational expression is false executes program statements following ELSE if used INPUT Prompt message variable variable variable R Displays a question mark and optional prompt message on the host computer and waits for keyboard input Stores input in variable s A comma before the first variable suppresses the question mark INT expression C R Returns integer portion of expression IP CR Retrieves or assigns a value to the 8052 s special function register IP LD expression C R Retrieves a 6 byte floating point number and places it on the argument stack Ex pression points to the most significant byte of the number LEN CR Returns the number of bytes in the current program LET variable expression C R Assigns a variable to the value of
29. we re interested in sensors that respond electrically by varying in voltage current or resistance since these are easily interfaced to electronic circuits One obvious use for sensors is in environmental monitoring including detecting and measuring temperature light wind speed and direction humidity and so on But all kinds of electronic devices use sensors even when sensing isn t the primary purpose For example computer printers have sensors that detect when the printer is out of paper Many cameras The Microcontroller Idea Book 153 Chapter 9 can sense light level and distance And modern automobiles contain all kinds of sensors including ones to measure engine temperature composition of exhaust emissions oil pressure engine speed and whether or not the seatbelts are fastened You can find a sensor to detect and measure just about any property Some sensors are readily available from suppliers of other electronic components These include photodiodes and solar cells which respond to light and semiconductors that respond to changes in tempera ture Surplus catalogs sometimes have good deals on sensors from failed or obsolete products for example dollar bill sensors from vending machines and motion detectors from security systems Sometimes you can make your own sensors from everyday materials The conductive foam commonly used to hold CMOS components can double as a simple pressure sensor since its top to botto
30. 1 40 PRINT Bit PORT1 AND 2 2 50 PRINT Bit PORT1 AND 4 4 60 PRINT Bit 70 PRINT Bit 80 PRINT Bit 90 PRINT Bit 100 PRINT Bit 110 END 8 PORT1 AND 10H 10H PORT1 AND 20H 20H 1 1 PORT1 AND 40H 40H PORT1 AND 80H 80H 1 NnNU BP WNEF O TA n ta PORT1 AND 8 ee on i es The Microcontroller Idea Book 41 Chapter 3 Listing 3 2 Allows you to set or clear individual bits of Port 1 10 INPUT Enter a bit to set or clear 0 2 4 7 X 20 IF X 3 THEN PRINT Do not change bit 3 GOTO 10 30 INPUT Enter 1 to set 0 to clear Y 40 IF Y 1 THEN PORTI PORT1 OR 2 X 50 IF Y 0 THEN PORT1 PORT1 AND OFFH 2 X 60 END Run the program and follow the on screen instructions to set or clear a bit To monitor a port bit as you set and clear it you can use a logic probe voltmeter or oscilloscope For example to monitor bit 0 place a logic probe on pin 1 of U1 or connect the lead of a voltmeter to pin 1 and the lead to ground Accessing Memory Listing 3 3 allows you to read and write to external RAM Here is an example of what happens when you run this program Enter 0 read 1 write or 2 quit 1 Free memory ranges from 397H to 1FFFH Enter an address to write to 1000H Enter data to be written 55H 55H has been written to address 1000H Enter 0 read 1 write or 2 quit 0 External RAM ranges from 0 to 1FFFH Enter an ad
31. 100 PRINT Interrupt detected 110 RETI For a pushbutton triggered interrupt connect a switch like Figure 7 1 s to the 8052 BASIC s INTI input at pin 13 Pin 13 will then be normally high When you press and release the switch pin 13 will briefly go low Listing 7 1 is a simple program that waits for interrupts and jumps to an interrupt handling routine when it detects one signified by pin 13 going low Line 10 enables external interrupt 1 and specifies line 100 as the location to branch to when the 8052 BASIC detects an interrupt request at pin 13 Lines 20 30 are an endless loop that waits for an interrupt Lines 100 and 110 are the interrupt service routine In this example the routine doesn t do very much it just displays an on screen message that the interrupt was detected then returns to the main program loop Edge detecting Interrupts BASIC 52 s TCON operator allows you to write to the 8052 s special function register TCON which enables you to set up interrupt 1 as edge detecting or level detecting The default after bootup or reset is edge detecting where interrupts are triggered by a falling edge at pin 13 If you want a rising edge to trigger an interrupt you ll have to add an inverter at pin 13 Edge triggering is handy for detecting switch presses because the interrupt routine executes only once when the switch is first pressed no matter how long you hold down the switch Switch debouncing Even with
32. 2 Voltage specifications for different types of logic powered at 5V Logic Type Output Input 0 maximum 1 minimum 0 maximum 1 minimum TTL including LSTTL 0 4V 2 4V 0 8V 2 0V most NMOS HCTMOS 0 1V 4 9V 0 8V 2 0V HCMOS 0 1V 4 9V 1 0V 3 5V 4000 series CMOS 0 1V 4 9V 1 5V 3 5V Table 3 2 summarizes the input and output voltage specifications for different logic device families The main point to remember is that a TTL logic high output voltage and most NMOS high outputs may be as low as 2 4V which does not meet the minimum input voltage requirement for HCMOS or 4000 series CMOS devices To interface a TTL output to CMOS use an HCTMOS device which accepts TTL logic inputs Or you may add a pull up resistor to a TTL output to pull it near 5V Serial Interface The final chip in the schematic is U5 a MAX232 driver receiver which is the popular single chip solution for RS 232 interfaces One side connects to the 8052 s serial input and output on pins 10 and 11 of U1 and the other side sends and receives signals at standard RS 232 levels to a personal computer Larger capacitor values for C4 C7 are fine and the MAX232A version can use values as small as 0 1 microfarad If you splurge on a MAX233 which has internal capacitors you don t need C4 C7 at all Power Supply A final essential component is the power supply For the basic system all you need is a regulated 5 volt supply These are widely available from mail
33. 20 A XBY OFEOOH tells you why you are executing the instruction The problem with adding comments to BASIC 52 programs is that they slow program execution They also make the program longer so that it needs more memory So you might want to keep comments to a minimum in the final version that you store in NV memory You can however store fully documented copies of your program on disk If you wish you can use your personal computer s text editor to add comments on unnumbered lines like this REM Read the states of switches 1 8 20 A XBY OFEOOh Then as you upload the program to your 8052 BASIC system all of the lines will display on the host computer but BASIC 52 will store only the numbered lines discarding the unnumbered remarks e Use short variable names for faster execution speed BASIC 52 allows variable names of up to eight characters Programs with shorter variable names will run faster and require less memory to store Even if you limit yourself to 1 and 2 letter variables you still have hundreds to choose from Longer names such as REVERSE QUIT and so on have the advantage of being more meaningful it s easier to guess their meaning without adding comments So there are times when you might choose a longer name But longer names can cause other problems as the next paragraph explains e Be sure that variable names don t contain keywords In BASIC 52 you can t name a variable ON because ON is already def
34. 20 steps 360 18 for one full rotation Using the resistor values shown and a motor with an 18 degree step angle the motor speed will vary from 1 to 15 Hz in wave drive or l phase mode For a different range of speeds use the formula shown to select resistor and capacitor values For speeds from 10 to 150 Hz use 0 01 microfarad for C1 or decrease the values of R1 R4 by a factor of ten The formula assumes that in the series R1 R4 each resistor is half the value of the preceding one If you use a different resistor scaling you ll have to calculate the values of the parallel combinations of resistors to find the resulting frequencies Bits 5 and 6 of the port select the operating mode Wave drive mode powers one phase at a time while two phase drive powers two phases at once and half step drive alternates The Microcontroller Idea Book 193 Chapter 11 Listing 11 3 Controls a stepper motor 10 20 30 40 50 60 70 80 90 100 110 120 130 REM A address of output port A 0E400H DO INPUT Speed 1 15 S INPUT Mode l wave 2 2 phase 3 1 2 step 4 stop M INPUT Direction 0 Clockwise 1 Counterclockwise D IF M 1 THEN X 4 IF M 2 THEN X 0 IF M 3 THEN X 2 IF M 4 THEN X 6 XBY A S X D 10H WHILE 1 1 END powering one and two phases Wave drive uses the least power but with reduced torque compared to 2 phase drive Half step drive uses twice as many steps per revolution and so offe
35. 4 5V in 10 milliseconds or less the module initializes automatically But if power up doesn t meet this requirement your program has to provide the initialization routine It s a good idea to always include an initialization routine in your program since it does no harm and if the module doesn t initialize properly it won t respond correctly or at all Table 8 3 summarizes the initialization procedure In short the module must first receive three identical commands selecting an 8 bit interface BASIC 52 easily provides the necessary delays between the commands To begin the initializing you must send the instruction to select an 8 bit interface even if your interface is four bits Once this is done the instructions for Function Set Display On Display Clear and Entry Mode Set tell the controller the configuration you desire The automatic power on initiali zation routine turns the display off so if you use it you have to turn the display on by writing OCh to the instruction register When initializing is complete you can control the display as you wish though you can t change the number of display lines unless you reinitialize from the beginning Listing 8 4 has two subroutines one for writing characters to the display and one for writing instructions To write a character set D equal to the character s code and call subroutine 800 which sets RS writes the character to the display and toggles E To write an instruct
36. 5V This causes the 8052 to run the BASIC 52 interpreter in ROM on boot up If EA is low the 8052 ignores its internal ROM and instead accesses external program memory on boot up You can wire EA directly The Microcontroller Idea Book 25 Chapter 3 to 5V or use a jumper as shown in the schematic to allow you to bypass BASIC 52 and boot to an assembly language program in external memory as described in Chapter 13 The crystal XTAL1 is an 11 0592 Mhz crystal that connects to pins 18 and 19 of U2 This crystal frequency has two advantages It gives accurate baud rates for serial communications due to the way that the 8052 s timer divides the system clock to generate the baud rates Plus BASIC 52 assumes this frequency when it times the real time clock EPROM programming pulses and serial printer port However you should be able to use any crystal value from 3 5 to 12 Megahertz If you use a different value you can use BASIC 52 s XTAL operator to adjust the timing to match the frequency of the crystal you are using The serial communications are reliable if the baud rate is accurate to within a few percent The higher the crystal frequency the faster your programs will execute so most designs use either 11 0592 Mhz or 12 Mhz which is the maximum clock frequency that the standard 8052 chip can use Capacitors C2 and C3 are 30 picofarads each as specified in the 8052 s data sheet Their precise value isn t critical Smaller va
37. 6 14 D7 1 0 Data bit 7 Memory Areas The HD44780 s on chip memory includes a CG character generator ROM CG RAM DD display data RAM an instruction register and a data register The CG ROM stores the segment patterns for generating 192 different characters including the Roman English alphabet in upper and lower case numbers some math and other special symbols and Japanese kana characters These are fixed in ROM and can t be altered The CG RAM stores segment patterns for up to 16 user designed characters such as logos special symbols or other simple graphics characters that you design on the 5 X 8 matrix To create a custom character you write a series of 5 bit words to the CG RAM Each word represents the segment pattern for one row in the desired character The patterns stored in CG RAM disappear on powering down so you must reload them on each time you power up The Microcontroller Idea Book 141 Chapter 8 Table 8 2 Instruction summary for the HD 44780 LCD controller Instruction RS RW D7 D6 D5 D4 D3 D2 D1 ODO Function Execution time max Display cear O 0 0 0 0 0 0 0 0 1 Clear display 1 64 Reset display from shift msec Set DD RAM 0 Display cursor 0 0 0 0 0 0 0 0 1 X Shift 0 1 64 home DD RAM 0 msec Entry mode o 0 0 0 0 0 0 1 D S WD increment 1 40 usec set decrement 0 cursor or display shift after data transfer S shift on 1 off 0 Display on off O0 0 0 0 0 O 1 D C B D display on
38. 8052 BASIC NTI A menu asks you what type of alarm you would like prompts you for additional information and stores the appropriate values in the DS1286 s registers 3 5 and 7 Line 2240 configures INTA as a low going pulse An endless loop at lines 2250 2270 then waits for an interrupt On interrupt the program displays the word ALARM and the current time and date You could place any program code in the interrupt routine For example you could read sensor data or write to a port to cause a stepping motor to increment 180 The Microcontroller Idea Book Clocks and Calendars Listing 10 3 page 1 of 4 Clock and alarm routines for DS1286 Watchdog Timer 10 REM set WT to match address of DS1286 watchdog timer 20 WT 0A000H 30 DO 40 PRINT 50 PRINT Select function 60 PRINT Initialize and start clock 1 70 PRINT Display time and day 2M 80 PRINT Set alarm BN 90 INPUT A 100 IF A 1 THEN GOSUB 200 110 IF A 2 THEN GOSUB 1000 120 IF A 3 THEN GOSUB 2000 130 WHILE 1 1 140 END 200 REM initialize and start clock 210 REM stop clock while initializing 220 XBY WT 9 XBY WT 9 OR 80H 230 REM get time and date convert each value to BCD and store 240 INPUT year 0 99 X 250 GOSUB 3000 260 XBY WT 0AH X 270 INPUT month 1 12 X 280 GOSUB 3000 290 XBY WT 9 XBY WT 9 AND OEOH X 300 INPUT day of month 1 31 X 310 GOSUB 3000 320 XBY WT 8 X 330 INPUT day of week 1 7
39. 9000 where 9000 is the line number where Listing 14 2 begins and follow the on screen instructions Listing 14 2 has all of the abilities of PROG1 PROG6 including auto execute on power up setting the baud rate and saving MTOP Line 8990 indicates the end of the program you want to save Lines 9000 9040 prompt you to press P to copy the current BASIC 52 program to NVRAM at U8 or press Q to quit Line 9050 writes 55h to NVRAM which indicates to the interpreter that a BASIC program follows Lines 9060 9080 copy the current BASIC 52 program which is stored beginning at 200h in external data memory U7 to NV RAM U8 beginning at 8011h Listing 14 2 is also copied as part of the current program Lines The Microcontroller Idea Book 243 Chapter 14 Listing 14 2 Simulates BASIC 52 s PROG and PROG1 6 commands for systems with BASIC 52 in external memory or systems that do not use the Pam PULSE Signal Adapted and reprinted with permission from Micromint 8990 END 9000 PRINT Press P to copy the current BASIC program to RAM at 8000h 9010 PRINT Press Q to quit 9020 G GET 9030 G GET IF G 0 THEN 9030 9040 IF G lt gt 80 AND G lt gt 112 THEN END 9050 XBY 8010H 55H 9060 FOR X 200H TO 200H LEN 9070 XBY X 7E11H XBY X 9080 NEXT X 9090 PRINT Press a number from 1 to 6 to do PROG1 PROG6 9100 PRINT Press Q to quit 9110 G GET 9120 G GET IF G 0 THEN 9120 9130 IF G lt
40. BASIC 52 s ON EX1 instruction will also respond to external interrupt 1 but the response time will be much slower ON EX1 has priority however and Listing 13 6 will not execute if an ON EX1 statement has executed in BASIC 52 e When BASIC 52 jumps to an assembly language interrupt routine it automatically pushes psw on the stack But popping psw on returning from the interrupt routine is not automatic so the interrupt routine must include an instruction to do so e Unlike other subroutines which end with ret interrupt routines must end with reti To test Listing 13 6 upload it to RAM at 4013h and execute these two lines of BASIC 52 code to ensure that the interrupt is enabled IE IE OR 84h TCON TCON OR 04h Now each time pin 13 goes low pin 1 should toggle as it did with Listing 13 1 Adding Custom Commands and Instructions Another feature of BASIC 52 is the ability to add up to 16 custom keywords representing commands or instructions that you define with assembly language routines Listing 13 7 is an example program for doing so To add custom keywords you must have code memory from 2000h to 2071h because BASIC 52 looks for special information at several addresses in this area On bootup BASIC 52 examines the data at address 204 8h If bit 5 is set BASIC 52 assumes that you have added custom keywords and it looks for additional information in a token table and vector table At 2078h BASIC 52 expects to find the sta
41. Because the amount of memory and interfaces that can fit on a single chip is limited microcontrollers tend to be used in smaller systems that require little more than the microcontroller and a few support components Examples of popular microcontrollers are Intel s 8052 including the 8052 BASIC which is the focus of this book Motorola s 68HC11 and Zilog s Z8 A Little History To understand how microcontrollers fit into the always expanding world of computers we need to look back to the roots of microcomputing In its January 1975 issue Popular Electronics magazine featured an article describing the Altair 8800 computer which was the first microcomputer that hobbyists could build and program themselves The basic Altair included no keyboard video display disk drives or other elements we now think of as essential elements of a personal computer Its 8080 microprocessor was programmed by flipping toggle switches on the front panel Standard RAM was 256 bytes and a kit version cost 397 498 assembled A breakthrough in the Altair s usability occurred when a small company called Microsoft offered a version of the BASIC programming language for it Of course the computer world has changed a lot since the introduction of the Altair Microsoft has become an enormous software publisher and a typical personal computer now includes a keyboard video display disk drives and Megabytes of RAM What s more there s no longer any nee
42. Distance 212 Radio Links 216 Calling Assembly language Routines Assembly language Basics 218 What You Need 218 Loading a Routine 221 File Formats for Assembly language Routines 222 Assembling a Program 224 Uploading a Program 225 Example Creating a Sine Wave 227 Avoiding Program Crashes 231 Interrupts 232 Adding Custom Commands and Instructions 233 A General purpose EPROM Programmer 237 Running BASIC 52 from External Memory Reasons 239 Copying BASIC 52 240 System Requirements 241 Storing BASIC 52 Programs 243 Related Products Enhanced BASIC 52 245 BASIC Compilers 246 Programming Environments 247 Pc Boards 248 BASIC 52 Source Code Sources Books 251 BBS s 254 Product Vendors 255 250 185 199 217 239 245 251 Appendix B Programs for Loading Files 263 Appendix C Number Systems 271 About Number Systems 271 Kilobytes and Megabytes 273 vi Introduction Introduction This book is a hands on guide to designing building and testing microcontroller based devices Microcontrollers or single chip computers are ideal for projects that require computer intelligence but don t need the overhead of a complete personal computer with disk drives keyboard and full screen display Why the 8052 BASIC This book focuses on the 8052 BASIC microcontroller which is easy to use full featured and inexpensive to work with The on chip BASIC 52 programming language enables you
43. Figure 11 3 shows The gain error is guaranteed to be 0 5 percent or less over the full range of operating temperatures The Microcontroller Idea Book 189 Chapter 11 DATA BUS 74LS3 7 DQ D7 Cheek 3006 OR LF13007 l IGITAL GAIN SET F D 1D SID IGINI ExT 2D QDIGIN2 Bout 3D QoIGIN3 aout H2 4D Cl l 6D 15V 7D INPUT 27 8D l ovouT E400H LF411 3 l Lei VINO T op AMP WRITE line 13 15V 7 4HCTO2 Bisa las R 14 fs i GWR RF Jis DGND AGND V V ee 16 ik is V 15V 15V GAIN TABLE DIG DIG DIG GAIN IN IN IN LE13006 LF 13007 l 2 3 AQUT BOUT AOUT BOUT Q Q l l l l l 2 2S2 l l Q 4 2 5 2 1 6 l l 8 5 4 l Q j 16 10 10 8 l Q l 32 20 20 16 l l 64 40 50 40 l l 1 11281 8 100 80 Figure 11 3 An LF13006 7 controls the gain of an LF411 op amp The bits that select the gain are outputs of a 74LS374 latch addressed at E400h The LF13006 7 s Chip Select and Write pins are tied low which causes the gains at pins 12 and 6 to immediately match the settings at DIGINI DIGIN3 If you want to control up to four gain set chips and op amps you can use the five remaining outputs of the 74LS374 to select the desired chip Tie all of the WR inputs to one bit and tie each CS input to one of the remaining bits Then to set the gain of an op amp bring its CS input low then bring WR low then high to latch the
44. OFC0O3H 82H 30 DO 40 INPUT Enter the decoder s address 0 15 A 50 INPUT Enter the data to send 0 15 D 60 REM Write the address and data information to Port A 70 XBY OFCOOH D 10H A 80 REM Toggle TE Port C bit 7 90 XBY OFCO3H 0EH 100 XBY OFCO3H OFH 110 WHILE 1 1 120 END Computer controlled Receiver Instead of or in addition to computer control of the transmitter you can also add a computer interface at the receiver For example a data logger might accept data from a remote transmitter and process the data or store it for later use Figure 12 7 shows a receiver similar to Figure 12 2 s with the manual controls replaced by port bits of an 82 C 55 The circuit uses different port bits from Figure 12 6 s circuit so you can connect both a transmitter and a receiver to one 8255 if you wish The low nibble of Port C is configured as an output and sets A1 A4 on the decoder As in the previous circuit A5 is tied high so you can set the address with 4 bits Port B is configured as an input and its bits 4 7 store the data received at the decoder s D6 D9 VT is inverted and then connects to the 8052 s INTI pin 13 You can use any CMOS inverter Listing 12 2 is a BASIC 52 program that sets up the 8255 to receive data at port B in Mode 0 The program writes an address to the decoder s address inputs and also turns off TE PC 7 in Figure 12 6 to ensure that the encoder on this end if co
45. OFFH rem Now load the number of bytes to program 1540 DBY 1Fh COUNT 256 DBY 1Eh COUNT AND OFFh rem Program the data into the part 1550 PGM IF DBY 1Fh OR DBY 1Eh lt gt 0 THEN GOTO 3060 1560 RETURN 1570 FOR I SOURCE TO SOURCE COUNT 1 XBY ADDR XBY I 1580 time 0 dby 47h 0 clockl do until time gt delay 1590 if xby addr lt gt xby i goto 3100 1600 addr addr 1 clockO next clockO return rem Convert the ASCII text to numbers 2000 C ASC S 0 I IF C lt 70 AND C gt 65 THEN C C 55_ELSE C C 48 2020 CH C 16 C ASC 0 I 1 2040 IF C lt 70 AND C gt 65 THEN C C 55 ELSE C C 48 2050 CH CH C RETURN rem Here when we are going to load the data into EEPROM 2100 WAIT 0 0005 RETURN rem Here for Intelligent programming 2110 WAIT 0 001 RETURN 268 The Microcontroller Idea Book Programs for Loading Files Listing B 2 page 4 of 4 rem Error messages and program termination 3000 PRINT CR Line LINE EXPECTED FOUND CHR C END 3010 PRINT CR Line LINE Unknown record type END 3020 PRINT CR Line LINE Checksum failure pected 3025 PHO ABS CHECK CH END rem Normal program exit point 3030 PRINT CR Received an End record in line LINE 3040 PRINT CR Line LINE Illegal EPROM EEPROM ad dress 3050 PHO ADDR END 3060 PRINT CR Li
46. R1 and R2 for each output voltage but you can power both LM317 s from the same supply Typical current requirements for programming an NMOS 2764A are 50 milliamperes at 12 5V and 75 milliamperes at 6V or 125 milliamperes total For a CMOS 27C64 it s 30 milliamperes for each or 60 milliamperes total Each regulating circuit uses an LM317 adjustable regulator You set the output voltage of the LM317 with R1 and R2 using the formula shown The LM317 creates a constant 1 25V reference across R1 The current through R1 also flows through R2 and the voltage across the pair of resistors is the regulator s output Intel s EPROM data sheets specify this range for the programming voltages The Microcontroller Idea Book 6 Chapter 4 EMSIZ VOUT 15V TO 18V DCOJYIN OUT REGULATED DC VOLTAGE ADJUST R1 LADJ SA0 IN ADJUST LM317 R2 VOUT 1 25 1 R IADJ R2 TYPICAL IADJ 50uA ADJUST R2 FOR DESIRED VOUT OR USE THESE VALUES FOR RI AND R2 TOLERANCE RESISTOR VOUT 5 1 R ANY 240 237 R2 12 5 2 2K 2 15K R2 6 910 931 Figure 4 6 Power supply circuit for EPROM programming voltages VPP 12V to 13V vcc 5 75V to 6 25V If you use 5 tolerance resistors for R1 and R2 you may have to vary the value of R2 for the proper output especially to meet the requirement for Vcc Or you can use a 5K potentiometer for R2 and adjust for
47. a power of 10 The Microcontroller Idea Book 271 Appendix C This table shows the value of each digit in the decimal number 93 Decimal digit 1 9 3 Digit multiplier 10 10 10 Digit value 100 90 3 Binary Numbers In the binary number system each digit represents a value raised to a power of 2 The numbers use only two of the ten decimal digits 0 and 1 Binary representations are useful when you need to quickly see the value of each bit in a byte For example you might want to set clear toggle or read a bit in one of the 8052 s special function registers TCON PCON and so on Or in a control circuit individual bits might control switches or relays BASIC 52 s logical operators offer a way to control and display individual bit values This table shows the value of each digit in 7700 0001 which is the binary representation of the decimal number 193 Binary bit 1 1 0 0 0 0 0 1 Bit multiplier 2 26 2 24 29 2 2 20 Bit value decimal 128 64 0 0 0 0 0 1 Hexadecimal Numbers In the hexadecimal or hex number system each character represents a value raised to a power of 16 There are 16 characters with the letters A through F representing the decimal values 10 through 15 Because each character in a hex number represents 4 bits hex numbers are a convenient compact way to express 8 bit or 16 bit numbers In BASIC 52 you enter hex values at the host system s keyboard by adding a trailing h to the number Exam
48. add a pull up resistor to ensure that high outputs are greater than 3 5 volts C To translate an output to a lower voltage use a 74HC4050 buffer or 74HC4049 inverter powered at the lower voltage D To translate an output to a higher voltage use a 74LS26 NAND or similar high voltage open collector gate with a pullup resistor to the higher voltage E For high current outputs you can use Texas Instruments 7545X series of peripheral drivers The 75452 NAND gate can sink up to 300 milliamperes at 0 5V F U14 can directly drive an LED Since the 74LS374 can sink more current than it can source connect the LED so that it turns on when the output is low With a 220 ohm current limiting resistor the LED s forward current is around 13 milliamperes G As with inputs an optocoupler is another way to interface different voltages and to electrically isolate an output from the microcontroller circuit Reading and Controlling Individual Bits Unlike assembly language for the 8052 BASIC 52 has no logical operators for setting and clearing individual bits in a byte But you can use the AND and OR operators to accomplish the same thing Listing 6 1 Displays the value of each bit at input port EO0Oh 10 A XBY 0E000H 20 PRINT Bit 0 30 PRINT Bit 40 PRINT Bit 50 PRINT Bit 60 PRINT Bit 70 PRINT Bit 80 PRINT Bit 90 PRINT Bit 100 END A AND 1 A AND 2 2 A AND 4 4 A AND 8 8 A AND 10H
49. and display the characters received at the serial port Also useful but not essential is the ability to upload and download text files from your disk over the serial link If you don t have a favorite communications program look in shareware catalogs or the file areas of online services or BBS s where you can try out the offerings for a small disk copying or downloading charge Test Equipment Some basic test equipment will help you monitor test and troubleshoot your circuits Minimum requirements include a multimeter capable of reading volts ohms and milliam peres Just about any basic meter will do for this A logic probe is convenient but not essential for monitoring logic levels and transitions Best of all an oscilloscope lets you view the actual waveforms on one or more channels Knowledge This book assumes that you have a basic knowledge of electronic circuits including digital logic It does not assume that you know a lot about computer programming and computer circuits Appendix A lists some books that cover the basics if you want to review or learn these Appendix C is a review of hexadecimal binary and decimal number systems The 8051 Family At the core of the 8052 BASIC is an 8052 microcontroller a member of the 8051 microcontroller family Intel Corporation introduced the 8051 in 1980 Since that time 8051 family chips have been used as the base of thousands of products Many other companies including Philip
50. application e What kind of output do I need analog digital voltage current 8 bit digital output would be ideal but analog voltage or current output is OK 154 The Microcontroller Idea Book Using Sensors to Detect and Measure e What power supplies are available to power the sensor 12V 5V The answers to these questions will help you narrow your choices as you research what s available On off Sensors Sometimes all you need to detect is the presence or absence of the sensed property Some simple sensors act like switches with a low resistance in the presence of the sensed property and a high resistance in its absence There are many types of sensors that you can use in this way A magnetic proximity sensor responds to the physical separation of the items connected to each of the switch elements A vibration sensor responds to rapid motion Both of these are often marketed as home se curity devices for use on doors or windows but you might come up with other uses for them Another example is a mercury tilt switch which uses a ball of liquid mercury as a conductor The switch contacts open or close when the switch tilts and the mercury rolls to the opposite end of the switch Figure 9 1 illustrates Figure 9 2 shows two ways to detect the state of on off sensors like these Figure 9 2A is an unlatched input When the resistance across the sensor is high the pull up resistor brings the input voltage high When th
51. as Figure 12 8D shows The IRF511 MOSFET turns on when a voltage is applied to its gate To turn on fully the MOSFET requires a gate voltage greater than 5 volts For more powerful transmissions to a specific receiver you can mount multiple IREDs in a cluster all pointing at the receiver If you want to transmit to multiple receivers or if a receiver s exact location is unknown you can mount the IREDs so that they transmit across a wider path Using Lenses Another way to increase the range of a link is with optical lenses that focus or spread the transmitted energy The Microcontroller Idea Book 215 Chapter 12 Some IREDs are manufactured with integral lenses that focus the output into a beam For example Harris FSD 1 and F5E1 IREDs are identical except that the F5D1 has a lens that aims the energy in a narrow beam while the F5E1 has a flat window and wider beam angle An IRED with an integral lens is an easy low cost option if it can do the job A flat window package is useful if you want to add an external lens or if you want a wider beam to reach multiple receivers around a room for example If you re interested in experimenting with lenses Edmund Scientific has a huge selection including inexpensive educational grade lenses lens mounts optical benches and books on optics Although infrared links are most often thought of as line of sight paths for transmitting across a room for example optics can also over
52. can do quite a bit with just these circuits Listing 3 4 Real time clock 10 CLOCK 1 TIME 0 SEC 0 20 DO 30 ONTIME 1 60 40 WHILE SEC lt 60 50 END 60 TIME TIME 1 70 SEC SEC 1 80 PRINT SEC 90 RETI Tne Microcontroller Idea Book 43 Chapter 3 Listing 3 5 This program uses BASIC 52 s GET instruction to detect when the user has pressed a key 10 CLOCK1 TIME 0 SEC 0 20 PRINT Press any key to quit 30 DO 40 ONTIME 1 100 50 G GET 60 UNTIL G lt gt 0 70 END 100 TIME TIME 1 110 PHO PORT 120 RETI Exiting Programs Some programs such as Listing 3 3 s continue to run until the user requests to end it In BASIC 52 there are several ways to detect that the user wants to stop a program Set a User Variable In Listing 3 3 the program displays a menu of choices on the host computer s screen The program continues to run until the user selects QUIT by entering 2 which sets the variable RW to 2 and causes the DO WHILE loop and the program to end Use GET Sometimes selecting a menu option isn t convenient or appropriate Listing 3 5 reads and displays the value of PORT1 once per second until the user presses any key at the host computer The program uses BASIC 52 s GET operator to detect a keypress GET stores the ASCII code of a keypress at the host computer Setting a varialble equal to GET line 50 causes GET to reset to 0 You can detect a keypress by reading GET periodically If GET L
53. computer External interrupts INTO and INTI are external interrupt inputs which detect logic levels or transitions that interrupt the CPU and cause it to branch to a predefined program location BASIC 52 uses INTO for its optional direct memory access DMA function Programming functions BASIC 52 s programming commands use three additional port bits ALEDIS PGM PULSE and PGM EN to control programming voltages and timing for storing BASIC 52 programs in EPROM or other nonvolatile memory Additional Control Inputs Two additional control inputs need to be mentioned A logic high on RESET resets the chip and causes it to begin executing the program that begins at 0 in code memory In the 8052 BASIC chip this program is the BASIC 52 interpreter EA external memory access determines whether the chip will access internal or external code memory in the area from 0 to FFFh In BASIC 52 systems EA is tied high so that the chip runs the BASIC interpreter in internal ROM on boot up Power Supply Connections And finally the chip has two pins for connecting to a 5 volt DC power supply VCC and ground VSS That finishes our tour of the 8052 BASIC chip We re now ready to put together a working system 22 Tne Microcontroller Idea Book Powering Up 3 Powering Up This chapter presents a circuit that enables you to start using the 8052 BASIC chip You can write and run programs and experiment with the BASIC 52 programming la
54. data to the desired chip You can use just about any op amp with this circuit Shown is an LF411 which has a wide bandwidth and low input offset and drift A 10 picofarad capacitor from the op amp s input 190 The Microcontroller Idea Book Control Circuits Listing 11 2 Demonstrates gain control of op amp 10 REM A address of output port 20 A 0E400H 30 DO 40 FOR I 0 TO 7 50 XBY A I 60 PRINT Gain I 70 PRINT Press any key to continue 80 G GET 90 DO G GET UNTIL G lt gt 0 100 NEXT I 110 WHILE 1 1 120 END to output adds stability as recommended by the LF13006 7 s data sheet I found that the capacitor did keep the op amp s output from oscillating at certain gain settings The LF13006 7 also has two matched uncommitted resistors of about 15K each which you can use as you wish Listing 11 2 steps through the available gains You can verify circuit operation by connecting a signal such as a sine wave output of a signal generator to VIN and monitoring VOUT with an oscilloscope To use the full range of gains the signal at pin 3 must be quite small For example if your input is 100 millivolts peak to peak at a gain of 128 the output is 12 8 volts Controlling a Stepper Motor Figure 11 4 shows an 8 bit output port controlling a four phase unipolar stepper motor Applying power to the motor s four phases or coils in sequence causes the motor to turn The port uses a 74HCT374 latch ad
55. edge at INTI then causes the program to jump to line 100 Lines 100 110 read the value of the keypress at ADO AD3 and use the lookup table to translate the key press into an ASCII code For example if the key labeled 7 is pressed Y3 goes low when X1 is scanned and the 74C922 s AD outputs identify the keypress as 1000 in binary or 8 decimal which the 8052 reads at EOOOh Line 100 ANDs ADO AD7 with OFh to clear bits 4 7 leaving 8 the value of the keypress In line 110 8 1FFOh 1FF8h and the value stored at 1FF8h in external memory is 55 which is the ASCII code for the numeral 7 Line 120 causes the character matching the keypress to display on screen The program then returns to the main loop to wait for another key press If you have a keypad with different encoding change the lookup table to match its layout Customizing the Interface Listing 7 3 does little more than test the interface but you can use the general idea in a specific project You can also assign special functions to individual keys In an EPROM programmer these might be Select device Program Verify and so on If the functions aren t labeled on the keys you can describe them in an on screen menu Press 1 to select device press 2 to program and so on Then when a keypress is detected instead of just displaying the value of the key your program would branch to a subroutine that corresponds to the 122 The Microcontroller Idea Book Switches and Ke
56. error message double check your wiring When the programming command executes pins 20 22 and 27 should toggle along with the address and data lines Running a Stored Program When you have a program saved you can run it from the NV memory BASIC 52 s RAM and ROM commands switch from RAM mode where BASIC 52 runs the program stored in RAM U7 to ROM mode where it looks in U8 for programs to run When you ve programmed successfully run your program by typing ROM RUN or RROM You can store multiple programs space permitting and run each by specifying its number For example to run the second program stored type RROM2 To return to editing programs in RAM type RAM Another useful command is XFER In ROM mode type XFER to copy the current program from ROM into RAM where you can edit it and then use FPROG to store the revised version in U8 if you wish Adding Bootup Options The commands FPROGI FPROG6 enable you to store additional information besides programs FPROGI saves the current baud rate and causes BASIC 52 to boot immediately to the READY prompt without waiting to receive a SPACE character FPROG2 saves the current baud rate and also tells BASIC 52 to automatically run the first program in NV 54 Tne Microcontroller Idea Book Saving Programs memory on bootup This is what allows you to disconnect the system from its host and run it as a stand alone system You can also permanently store a value fo
57. expression Use of LET is optional LIST line number line number C R Displays the current program on the host computer LIST line number line number C R Writes the current program to LPT pin 8 LIST line number line number C R Writes the current program to a user written assembly language output driver at 40C3h Setting bit 7 of internal data memory location 27H enables the driver 78 Tne Microcontroller Idea Book Programming LOG expression C R Returns natural logarithm of expression MTOP highest address in RAM program space C R Assigns or reads the highest address BASIC 52 will use to store variables strings and RAM programs Usually 7FFFh or lower since EPROM space be gins at 8000h NEW C Erases current program in RAM clears all variables NOT expression C R Returns 1 s complement inverse of expression NULL integer C Sets the number 0 255 of NULL characters ASCII 00 that BASIC 52 sends automatically after a carriage return Only very slow printers or terminals need these extra nulls ON expression GOSUB line number line number line number R Transfers program control to a subroutine beginning at one of the line numbers in the list The value of expression matches the position of the line number selected with the first line number at position 0 Examples X 1 ON X GOSUB 100 200 400 Transfers program control to a subroutine at line 200 position 1 in the list X 0
58. has a 50 percent duty cycle the IRED is on for half of this time or 45 percent of each transmission If you send a lot of 0 s if the receiver s address is 00 for example or if you send only occasional short transmissions the average current will be much less In Figure 12 8A with R2 at 30 ohms the peak current through the IREDs is about 50 milliamperes and the average current is under 25 milliamperes well below the 100 mil liampere limit Even at a peak current of 150 milliamperes the average over each transmis sion cycle will be under 70 milliamperes still a safe level If you do pulse the IRED at 100 milliamperes or more you have to be very careful to design your circuit so that the IRED never comes on continuously When not transmitting data the IRED should be off At higher currents it s a good idea to use a current limiting resistor with a 1 2 watt or greater power rating Parallel drive If two IREDs aren t enough you can add two more in parallel as Figure 12 8B shows The value of the current limiting resistor is smaller because it has twice the current through it but the same voltage drop across it Figure 12 8C shows four IREDs powered by an NPN transistor A 74HC4049 inverter controls the transistor s base current With multiples of this circuit you can have as many IREDs as your power supply can support 12V drive And finally if you have a 12 volt supply available you can add up to six IREDs in series
59. in the stack area is called pushing or placing values on the stack Retrieving values from the stack area is called popping them off the stack Assembly language has push and pop instructions for accessing the stack BASIC 52 s PUSH and POP instructions access a separate area called the argument stack You can also preserve values by selecting a unique register bank for use by a routine The 8052 has 32 registers arranged in four banks of eight from 0 to 1 Fh in internal data memory You can access the registers by specifying the address or by selecting a register bank and specifying a register from RO to R7 within the bank For example if bank 0 is selected RO is location 00h but if bank 1 is selected RO is location O8h BASIC 52 uses banks 0 1 and 2 but uses bank 3 only with the PGM instruction so this bank is usually free for other uses Bits 3 and 4 of the 8052 s program status word psw select the register bank When you call an assembly language routine BASIC 52 automat ically selects register bank 0 To select bank 3 add this to the beginning of your routine push psw Save program status word orl psw 18h select register bank 3 The Microcontroller Idea Book 231 Chapter 13 Listing 13 6 This assembly language routine is similar to Listing 13 1 except that external interrupt 1 causes the routine to run On external interrupt 1 Port 1 bit 0 is complemented org 4013h vector for external jinterrupt 1 cp
60. is a program that displays the value of each of the bits in the port Enter each line carefully Be sure to include all of the punctuation shown When you run the program you should see a display like this AO The Microcontroller Idea Book Powering Up PORT 1 Bit Values Bit 0 1 Bit s 1 Bit 2 1 Bit 3 i Bit 4 1 Bit 5 1 Bit 6 1 Bit 7 1 If a port pin is open or unconnected its internal pull up resistor will cause it to read as 1 If you connect a jumper wire from a port pin to ground or bring the pin low by driving it with a logic low output it should read 0 Line 10 in Listing 3 1 brings all of Port 1 s bits high which enables them to be used as inputs Writing to Port 1 You can control the bits of Port 1 by writing to them Listing 3 2 allows you to set or clear individual bits Here s an example of what happens when you run the program Enter a bit to set or clear 0 2 4 7 7 Enter 1 to set 0 to clear 0 Enter a bit to set or clear 0 2 4 7 3 Do not change bit 3 The program doesn t allow you to change bit 3 P1 3 because the 8052 BASIC circuit requires this bit to be high when accessing external memory assuming that you ve included U3B in your circuit If you do clear bit 3 accidentally you ll crash the system and will have to reboot Listing 3 1 Displays the value of each bit in Port 1 10 PORTI OFFH 20 PRINT PORT 1 Bit Values 30 PRINT Bit PORT1 AND
61. is the reverse when the switch is open the pull down resistor brings the input low When the switch closes it connects to 5V and reads high You can connect a switch to an unused bit on the 8052 BASIC s Port 1 to an input on an 8255 PPI or to a input on a 74LS244 buffer The 8052 BASIC has internal pullups that bring the inputs to 5 V when they are not being driven by another source So if you connect The Microcontroller Idea Book 109 Chapter 7 5V a A TOGGLE ANY INPUT PORT BI OR 1 OPEN SLIDE Q CLOSED SWITCH 5V B TOGGLE OR SLIDE SWITCH ANY INPUT PORT BI 1 CLOSED 1 5K Q OPEN Figure 7 1 Youcan detect the state of a toggle or slide switch at an input port switch A to one of these inputs the external pull up is optional The pulldown resistor for switch B is 1 5K to ensure a valid logic low for LSTTL inputs With an 8052 BASIC or CMOS input you can use a 10K pulldown resistor If you want to offer a choice among several options a rotary switch can do the job Figure 7 2 shows an 8 position switch connected to an 8 bit input port Reading a Switch To find the state of a switch you read the byte at its address and use BASIC 52 s logical operators to find the value of the bit of interest just as you did when reading input ports in Chapter 6 For example to find the logic state of a switch at bit 7 of an input port at E000h use this statement A XBY 0E000H
62. its longer write times The program erases all of the stored programs and any options selected with FPROG1 6 in U8 Adding more NVRAM or EEPROM If you want to add an additional 8K of NV RAM or EEPROM wire another circuit exactly like Figure 4 3 s except connect pin 20 of the new NVRAM or EEPROM to A000h pin 10 of U4 ORed with RESET so that the chip will be accessed from A000h to BFFFh Adding EPROM Adding EPROM requires more circuitry than NVRAM or EEPROM because an EPROM must have a programming voltage at its VPP pin during programming To use the faster FPROG commands which follow Intel s Intelligent programming algorithm you should also raise the EPROM s supply voltage VCC to 6 volts during programming Although EPROMs do require additional components once you have them in the circuit you can use the 8052 BASIC system as a general purpose EPROM programmer as described in Chapter 13 You can store assembly language programs or any information that you want to save in EPROM whether it s for use by the 8052 BASIC system or another project EPROM Types Since EPROMs were first developed in the 1970 s each generation of devices has allowed larger capacities faster programming and reduced programming voltages Although the recommended programming algorithms or procedures for EPROMs are alike in many ways the details often vary depending on the device and manufacturer Programming Algorithms For critical appl
63. keywords and conventions When the program is complete the compiler program translates your program lines into the machine codes required by the 8052 chip The compilers will create an object file usually in Intel Hex format for uploading or programming into EPROM plus a listing file for documentation and debugging use When the object file is stored in the 8052 s code memory the 8052 can run the program directly without having to use the BASIC 52 interpreter Using a compiler has several advantages e Unlike with assembly language the syntax used with BASIC compilers is similar to BASIC 52 This means that you don t have to learn a new programming language In fact you can usually use the BASIC 52 interpreter to test your code before you compile it You can also use BASIC 52 for loading and debugging your compiled programs as described in Chapter 13 e A compiled BASIC program will run faster than an interpreted BASIC 52 program The speed increase depends on the program but programs that run 20 to 50 percent faster are typical e Because a compiler doesn t limit you to the 8052 BASIC chip you can develop programs for other members of the 8051 family For example Systronix s BASIC compiler has optional language extensions for Dallas Semiconductor s DS5000 8051 compatible microcontroller A disadvantage to using a compiler rather than an interpreter is that you have the extra steps of compiling and uploading programs before
64. lt gt 0 AND ADDR lt 8000H AND CH 0 THEN GOTO 3040 1390 RECORD CH rem Get the individual bytes accumulate them in the check sum and store rem them in memory 1400 INDEX SOURCE FOR I 10 TO 10 COUNT 2 STEP 2 GOSUB 2000 rem Here we deal with the data bytes not executed when RE CORD is type 1 1410 CHECK CHECK CH 1420 IF RECORD 1 THEN GOTO 1440 1430 XBY INDEX CH INDEX INDEX 1 NEXT rem Calculate the checksum 1440 CHECK CHECK ADDR 256 ADDR AND OFFH COUNT RE CORD AND OFFH 1450 IF CHECK lt gt 0 THEN GOTO 3020 1460 IF RECORD 1 THEN GOTO 3030 1470 PRINT CR Storing a Data record of COUNT bytes at PHO ADDR rem Retreive the data from memory and store them in the proper addresses 1480 on type gosub 1500 1570 1520 1520 1520 rem Restore our variables and continue 1490 ADDR 0 CHECK 0 GOTO 1340 Tne Microcontroller Idea Book 267 Appendix B Listing B 2 page 3 of 4 rem Store the data in RAM 1500 FOR I SOURCE TO SOURCE COUNT 1 XBY ADDR XBY I rem Now verify that stored data is readable as code 1505 if XBY I lt gt CBY ADDR THEN GOTO 3130 1508 ADDR ADDR 1 NEXT 1510 RETURN rem Store the data in EPROM or RDY BUSY EEPROM rem First load the source address registers 1520 DBY 1BH SOURCE 256 DBY 19H SOURCE AND OFFH rem Now load the destination address registers 1530 DBY 1AH ADDR 1 256 DBY 18H ADDR 1 AND
65. may have to slow Listing Listing 14 1 Copies the BASIC 52 interpreter program from ROM to NVRAM 10 PRINT copying BASIC 52 from ROM to RAM at 8000h 20 FOR I 0 TO 1LFFFH 30 XBY I1 8000H CBY I 40 NEXT I 50 PRINT verifying 60 X 0 70 FOR I 0 TO 1LFFFH 80 IF XBY I 8000H lt gt CBY I THEN GOSUB 120 90 NEXT I 100 IF X 0 THEN PRINT Copy successful 110 END 120 PHO Error at location I 130 X 1 140 RETURN 240 The Microcontroller Idea Book Running BASIC 52 from External Memory 14 1 for longer delays between writes To do so between lines 30 and 40 add this or a similar do nothing loop FOR J 1 to 10 NEXT J For EPROM storage you can copy the ROM into RAM and then use Listing 13 8 to program an EPROM For this method use a 32K RAM at U7 in Figure 3 1 You ll also need an unprogrammed 8K EPROM accessed as data or code data memory Set MTOP to 5FFFh or lower to ensure that BASIC 52 won t overwrite the area from 6000h to 7FFFh In Listing 14 1 lines 10 30 and 80 change 8000h to 6000h Run the revised program to copy the 8052 BASIC s ROM into RAM at 6000h 7FFFh You then can upload or enter Listing 13 8 to copy BASIC 52 into your EPROM at the starting address you specify Another option is to use an EPROM programmer to copy BASIC 52 If your programmer has an adapter for 8051s you can copy the 8052 BASIC s ROM directly into the program mer s buffer and then program an
66. minutes and hours But if you know the crystal s frequency you can measure seconds by counting the oscillations of the crystal This is what BASIC 52 s real time clock does A CLOCK1 statement starts the real time clock which causes the TIME operator to increment every 5 milliseconds Reading the TIME operator tells you the number of seconds that have passed since the clock was enabled CLOCKO stops the clock and freezes TIME at its current value TIME resets to 0 when the count reaches 65536 seconds 18 hours 12 3 minutes or when the statement TIME 0 executes If you stop the clock and then then restart it TIME will continue counting from where it left off unless you first reset it to 0 The ONTIME instruction jumps to a subroutine whenever TIME reaches the value you specify Because the ONTIME subroutine is an interrupt routine you use RETI not RETURN to end it Listing 10 1 is a program that counts seconds minutes and hours and displays the current reading once per second For accurate timekeeping the XTAL operator must match the value of your timing crystal You can also use ONTIME to trigger periodic operations Listing 10 2 is a program that toggles bit 7 of Port 1 once per second and displays the logic state of the bit after each toggle Clock Accuracy The more accurate your timing reference the more accurate your clock will be You can tune the frequency of a crystal slightly by varying the value of one of the capaci
67. of 250 nanoseconds or less are fine for the NVRAM Don t be confused by the fact that Dallas describes its devices by the number of bits they store rather than the number of bytes For example they call the 8 kilobyte DS1225 a 64K device You can order NVRAMs directly from Dallas Semiconductor no minimum order and from other vendors EEPROM The other option for program storage is EEPROM A typical EEPROM is guaranteed for 10 000 to 100 000 write cycles compared to infinite write cycles for NVRAM Access times for reading an EEPROM are similar to those for static RAM but writing to EEPROM takes much longer Most require 2 to 10 milliseconds after a write operation before you can access the chip again In spite of the drawbacks I ve included EEPROM as an option because an 8K EEPROM may cost less than a comparable NVRAM A typical part number for an 8K EEPROM is 2864 or 28C64 Figure 4 2 shows the pinout for a 28 C 64 EEPROM Notice that its pinout too is very similar to that of a 6264 static RAM EEPROMs have two common ways of indicating that they are busy performing a write operation and are unable to be accessed In one type when the EPROM is busy the data pins hold the last written data but with one or more bits inverted BASIC 52 s programming The Microcontroller Idea Book 49 Chapter 4 2864 5 28C64 2865 ONLY BUSY VCC Al2 2 WE A7 3 NC A6 4 A8 A5 5 AQ A4 6 All A3 7 OE A2 8 A1 Al 9 CE AQ DQ7 DOO DQ
68. of month 1260 X XBY WT 8 1270 GOSUB 3100 1280 PRINT X 1290 REM get year 1300 X XBY WT 0AH 1310 GOSUB 3100 1320 PRINT X 1330 REM get day of week 1340 X XBY WT 6 1350 GOSUB 3100 1360 PRINT Day of week X 1370 REM set TE when reads are done 1380 XBY WT 0BH XBY WT 0BH OR 80H 1390 RETURN 2000 REM set alarm 2010 PRINT Select alarm type 2020 PRINT Once per minute 1 2030 PRINT When minutes match 2 2040 PRINT When hours and minutes match 3 2050 PRINT When hours minutes and days match 4 2060 INPUT AF 2070 REM clear all 3 alarm mask bits 2080 XBY WT 3 XBY WT 3 AND 7FH 2090 XBY WT 5 XBY WT 5 AND 7FH 2100 XBY WT 7 XBY WT 7 AND 7FH 2110 REM set alarm mask bits as needed 2120 IF AF lt 4 THEN XBY WT 7 XBY WT 7 OR 80H 2130 IF AF lt 3 THEN XBY WT 5 XBY WT 5 OR 80H 2140 IF AF 1 THEN XBY WT 3 XBY WT 3 OR 80H 2150 IF AF gt 1 THEN INPUT Minute M 2160 IF AF gt 2 THEN INPUT Hour H 2170 IF AF 4 THEN INPUT Day D The Microcontroller Idea Book 183 Chapter 10 Listing 10 3 page 4 of 4 2180 2190 2200 2210 2220 2230 2240 2250 2260 2270 2280 3000 3010 3020 3100 3110 3120 3200 3210 3220 3230 184 REM store alarm settings IF AF1 THEN X M GOSUB 3000 XBY WT 3 80H X IF AF2 THEN X H GOSUB 3000 XBY WT 5 80H X IF AF 4 THEN X D GOSUB 3000 XBY WT 7 80H X REM turn o
69. opens the debouncing must time out before a new key press is detected The debounce period varies directly with capacitor size with larger values increasing the time By experimenting with different values you can adjust the timing until all key bounces are ignored yet no noticeable delay is required between key presses Adding a Keypad Figure 7 9 shows the 74C922 connected to the 8052 BASIC system The 74C922 interfaces the keypad to a 72LS244 buffer as described in Chapter 6 The 74C922 is shown addressed at E000h but you can use any available chip select Pin 13 of the 74C922 is tied low to permanently enable the data outputs Keypresses are read by reading the buffer at EOOOh The keypad s X and Y lines connect to their corresponding pins on the 74C922 Data outputs A D connect to D0 D3 on the 8052 s data bus DA which signals when a key has been pressed connects to INTI on the 8052 BASIC If you want to use polling to detect keypresses you can use any input port pin instead of INTI DATA BUS D D7 74LS244 718 ie IYI JAIL i DOUT A x H xI a jaliy LARS S DOUT B x2 H2 51 x2 Seale A DOUT C x38 ace iya a DOUT D x4 5X4 a 2A y H F 2Y2 2A2 r y2 Y2 A OE y3 w H M F var Y4 5 IG Osc s Rina 8x8 aai 6 olz AN mi oy READ ENCODE E 9 CI A
70. pin 30 of U2 is toggling at 1 6 the crystal frequency if you have an oscilloscope to measure This indicates that the oscillator circuit is functioning e Verify that pins 21 28 and 32 39 of U2 toggle as BASIC 52 performs its memory check immediately after powering up or rebooting e If all else fails recheck your wiring for missing or misrouted wires Sometimes there s no alternative but to go through the schematic connection by connection checking each with an ohmmeter The Microcontroller Idea Book 37 Chapter 3 Basic tests When your system boots you re ready for some basic tests The BASIC 52 programming manual is a useful reference at this point In some ways BASIC 52 is similar to BASIC compilers like Microsoft s QuickBASIC Many of the keywords and syntax rules are similar But BASIC 52 is closer to older interpreted BASICs like GW BASIC or BASICA You can type a statement or command and execute it immediately when you press ENTER or you can type a series of statements and run them later as a program When a line begins with a line number BASIC 52 treats it as a program line rather than as a command to execute immediately Here are some quick tests and experiments you can do Memory Check Type PRINT MTOP to learn the amount of external data memory that BASIC 52 detected on boot up With an 8K RAM MTOP should be 8191 and with 32K it should be 32 767 If you prefer hexadecimal notation type PHO MTOP In P
71. possibility for those who have access to a logic compiler and device programmer But for many circuits complete decoding of memory isn t necessary and less than complete decoding using off the shelf parts is more practical An Output Port To complement U12 s input byte U14 provides eight bits of output U14 is a 74LS374 octal flip flop which is very similar to the 74HCT373 octal latch at U4 On the 373 1Q 8Q follow 1D 8D until pin 11 goes high after which 1D 8D no longer change In contrast on the 374 1Q 8Q change only on pin 11 s rising edge when 1D 8D are latched to 1Q 8Q Here again I chose LSTTL over CMOS this time because the LSTTL device can sink 12ma at 0 25V compared to 6ma at 0 2V for the 74HC374 However the 74HC374 can also source 6ma at 4 2V so it s a better choice if you need to draw current from a logic high output U14 s eight data inputs connect to the data bus D0 D7 Its output control pin 1 is tied low so that the outputs are always enabled If you want to be able to disable the outputs you can instead tie pin 1 to an unused bit on Port 1 NOR gate U13A clocks U14 only when U2 writes to addresses from E400h to E7FFh When this occurs the data written is latched to the outputs of U14 The outputs do not change until the next time the chip is written to In the circuit U14 is write only Reading address E400h will return the value OFFh To access U14 at a different address wire pin 2 of U13A
72. respond to the longer wavelength emissions from GaAs and GaAlAs IREDs Although the GaAs IREDs are a closer match at 940 nm the GaAlAs IREDs tend 5V OV A B RI Q1 RI px Ql pEr P mps2907 U MPS2907 SV OFF 330 5V OFF 330 N QV 0 QV ON i R2 J R2 I PEAK RED CURRENT I PEAK IRED CURRENT SZ E XZ RO WO WO i I mA R2 0 mA R210 XZ XZ 50 30 VSS 50 15 J Ss RAN 100 15 10 8 2 150 10 150 5 6 D 12V R3 en R3 6 2 FOR 15QmA SZ PEAK IRED CURRENT va SZ C i AN g TS R2 11Q FOR 15QmA l d PEAK IRED CURRENT r AX SZ Wt TR SZ X SZ SZ RE TT AS Ha IRF511 RI RI 2N2222 5V OFF 330 SV OFF 1K V ON 74HC4049 QV ON 2N2222 Figure 12 8 Circuits to increase the power and transmitting distance of an infrared link A IREDs in series B IREDs in parallel with PNP transistor driver C IREDs in parallel with NPN transistor driver and D MOSFET driver The Microcontroller Idea Book 213 Chapter 12 to be more efficient so they may work as well even though 880 nm isn t as good a match with the detector Alternate Drive Circuits for IREDs You can increase the strength of an infrared signal in two ways by increasing the current through the IREDs or by increasing the number of IREDs Figure 12 8 shows both options in a variety of circuits All connect to the output of the NA
73. that controls the time base is stored at 4Ah in internal data memory At 12 Mhz it s 64h If you want to experiment change the value of XTAL then type PHO DBY 4AH to find out if the time base has changed A Watchdog Timekeeper Dallas Semiconductor s DS1286 Watchdog Timekeeper shown in Figure 10 1 is another way to keep track of time The chip is easy to use because it contains its own quartz crystal timing reference plus a lithium cell for backup power Once you initialize the clock and calendar and start the oscillator the clock keeps time for ten years or more whether or not an external power source is present You don t have to reset the clock every time you power up The DS1286 can be especially useful in battery powered systems Since it continues to keep time when the main power supply is off you can use its interrupt output to power circuitry at programmed times or intervals For example by adding circuits to control a power supply the DS1286 s interrupt could trigger a data logger or other instrument to power up at a programmed time After taking data or performing other operations the instrument could power itself down until the next interrupt from the DS1286 The longer the time between readings the greater the power savings 174 The Microcontroller Idea Book Clocks and Calendars INTE
74. the ADC0848 can measure Most of the solar cell s current flows through the 1 ohm resistor to ground Since the solar cell s voltage is only about 0 5 volt the power dissipated by the 1 ohm resistor is only about 0 15 watt in full sun About one percent of the solar cell s output flows through the 100 ohm resistor This same current flows through the 1 6K resistor with the result that the voltage at pin 1 of the LF353 varies from 0 to about 4 75V This voltage is proportional to the intensity of the light hitting the solar cell The second op amp is an inverter that converts the voltage to positive levels that the ADC0848 can measure Listing 9 4 assumes that pin 7 of the LF353 connects to Channel 8 of the ADC0848 On request the program converts the analog input and displays the result 166 The Microcontroller Idea Book Using Sensors to Detect and Measure Listing 9 4 Measures and displays solar energy detected by solar cell circuits at Channel 8 of ADC0848 10 REM set A to address of ADC 20 A 0C000H 30 REM set C to channel to read 1 8 40 C 8 50 REM use single ended mode select channel start convert 60 XBY A 8 C 1 70 REM FS full scale voltage 5V full sun output 4 75V 80 FS 1 05 90 B XBY A 100 T INT FS B 100 2554 5 110 PRINT Solar energy T percent of full sun 120 PRINT press any key to take another measurement 130 D GET IF D 0 THEN GOTO 130 140 GOTO 60 150 END Level Translat
75. the appropriate register The DD RAM stores up to eighty 8 bit character codes Each character position on the display corresponds to an address in the DD RAM and the character codes stored in the DD RAM determine what is displayed at each position On power up on a 2 line display the leftmost position on the top line has an address of 0 with the rest of the positions in the line addressed in sequence The second line begins at 40h even if the top line has fewer than 40h positions The instructions allow you to configure a module so that the DD RAM s address increments each time a character is written to the display This way the characters automatically appear in sequence on the display without your having to specify an address each time Because the second line begins at 40h however the display will not wrap around automat ically to this line For example on a 2 line 16 position display line 1 ends at OFh and line 2 begins at 40h To move from the rightmost position of line 1 to the leftmost position of line 2 you have to change the address counter to 40h In addition some displays with a single physical line of characters have two logical lines In a 16 character display of this type the first 8 characters are addressed from 0 to 7 and the second 8 are addressed from 40h to 47h With this type of display you must set the address counter to 40h before you write to the second half of the line On a small display where all 80 by
76. the entire area from 0 to 7FFFh The 8052 also has 256 bytes of internal data memory which the memory map doesn t show Two 8K blocks of combined code data memory are reserved beginning at 8000h As Chapter 4 showed BASIC 52 s programming commands store programs in nonvolatile memory beginning at this location For the input and output or I O circuits described in this chapter the memory map reserves the top block of data memory from E000h to FFFFh I O interfaces include connections to buffers latches switches displays motors or just about anything besides the system s main memory The I O circuits don t have to use this block but BASIC 52 encourages it since it clears external memory only up to E000h on bootup unless you specify a lower value by saving MTOP with a PROG3 command EXTERNAL MEMORY oe oie en UNASSIGNED cooo EXPANSION Je oogy DATA OFFA ease CODE UNASSIGNED UNASSIGNED COOH COOOH H COMBINED CODE DATA ONVOLATILE MEMO CODE INTERNAL MEMORY IFFFH DATA ROM CODE ogggH BASIC 52 Figure 6 1 Memory map for the 8052 BASIC system s internal and external data and program memory 88 The Microcontroller Idea Book Inputs and Outputs Unassigned space remains in the memory map but there s nothing wrong with this since it leaves room for additions Also this isn t the only way to configure an 8052 BASIC system For example i
77. the same procedure for the other keys As you progress you may detect a pattern that makes it easier to guess which pins will correspond to each keypress Some keypads don t seem to correspond to any obvious layout however When you know how the keypad decodes you can wire the connections and write your programs to match 118 Tne Microcontroller Idea Book Switches and Keypads Custom Keypads It s also possible to create a keypad with legends that match your application One source for these in single or small quantities is Sil Walker which offers a variety of membrane keypads in kit form A kit consists of the basic keypad optional colored pads a faceplate and a bezel To create a custom keypad you apply an optional colored pad and your own legend to each key You can apply a legend using silk screen printing transfer lettering or a felt marker You then press the faceplate over the keypad and press the bezel onto the faceplate and its mounting surface to secure the keypad in its final location Using a Matrix encoded Keypad In a matrix encoded keypad the usual way to detect a keypress is with scanning circuits In Figure 7 7 s keypad rows Y1 Y4 could be tied high through pull up resistors Columns X1 X4 could then be scanned or brought low in sequence As each column goes low the logic level at each row is checked repeating until a row goes low indicating that a key is pressed The column and row that are low identify
78. to control an infrared transmitter The encoder s transmit enable TE input connects to Port C bit 7 on the 8255 which you can set and clear with the 8255 s bit control instructions Listing 12 1 shows a BASIC 52 program that causes the Figure 12 6 s encoder to send a 4 bit value to Figure 12 2 s decoder The program asks for an address and data to transmit writes the information to Port A and then brings bit 7 of Port C low then high to cause the encoder to transmit the information If the transmitted address matches the decoder s the transmitted data appears at the decoder s data outputs and its VT valid transmission output goes high If the addresses do not match or if the decoder detects an error in transmission VT remains low and the decoder ignores the data If you want to do everything with a single 8 bit port you can tie another of the encoder s address inputs high or low or leave it open and use the additional bit on Port A to control TE If you do this you Il have to use Boolean operators AND OR to ensure that the data and address don t change when you toggle TE If you know you are going to transmit to only one address you can hard wire all of the encoder s address inputs and free up four bits on the 8255 for other uses The Microcontroller Idea Book 209 Chapter 12 Listing 12 1 Causes an encoder to transmit requested data 10 REM 8255 mode set Ports A C output Port B input 20 XBY
79. to select up to 16 motor speeds with four port bits 196 The Microcontroller Idea Book Control Circuits Listing 11 5 Controls direction and speed of Figure 11 6 s DC motor 10 REM A base address of 82C55 20 A 0FCO0OH 30 REM configure 8255 for all outputs 40 XBY A 3 80H 50 INPUT Direction 0 or 1 D 60 IF D 0 THEN XBY A 3 OEH ELSE XBY A 3 0FH 70 INPUT Speed 0 15 S 80 XBY A S 90 REM bring 555 s Reset PC 6 high off 100 XBY A 3 0DH 110 xXBY A S 120 G GET 130 DO G GET UNTIL G lt gt 0 140 REM Remove 555 s Reset 150 XBY A 3 0CH 160 END low pulses will be 10 000 microseconds or 10 milliseconds wide For accurate time calculations set XTAL to match your crystal s frequency In Listing 11 4 the number of cycles is 1 so the PWM statement results in one low pulse followed by one high pulse Lines 100 110 then use a GET operator to check to see if the user has pressed a key and if not the PWM output repeats Checking for a key press enables you to stop the program since BASIC 52 ignores CONTROL C keypresses while a PWM statement is executing The DO loop in the program results in a delay between each PWM statement During the delay P1 2 is high so the motor is powered Because of the delay with a 12 Megahertz crystal if L 1200h and H 25 P1 2 will have equal on and off times of about 5 milliseconds Increasing L will lower the motor s speed and decreasing L or
80. waits for the user to enter a 4 digit hex address then displays the data stored at that address in external RAM The Microcontroller Idea Book 123 Chapter 7 Listing 7 4 Reads the data stored a a 4 digit address entered by the user on a keypad 1 REM lookup table stores the numeric value of each key 10 ee REM 1 11 XBY 1F01H REM 2 12 XBY 1F02H REM 3 13 XBY 1F03H 0CH REM C 14 XBY 1F04H 4 REM 4 15 XBY 1F0O5H 5 REM 5 16 a ee E REM 6 17 XBY 1F07H 0DH REM D 18 a ney aoe REM 7 19 XBY 1F09H 8 REM 8 20 XBY 1FOAH 9 REM 9 21 XBY 1FOBH 0EH REM E 22 XBY 1FOCH OAH REM A 23 XBY 1FODH 0 REM 0 24 XBY 1FOEH x REM B 25 XBY 1FOFH REM F 30 A 0 40 COUNT 3 50 PRINT Please enter a 4 digit hex address to read 60 DO 70 ONEX1 100 80 WHILE 1 1 90 END 100 KEY XBY 0E000H AND OFH REM read the key 110 DAT XBY 1F00H KEY REM find its value 120 A A DAT 16 COUNT REM add to the total 130 COUNT COUNT 1 REM keep track of of digits read 140 PHO DAT 150 IF COUNT 1 THEN GOSUB 200 wait for 4 digits 160 RETI 200 PRINT PHO XBY A is stored at address A 210 PRINT Please enter another 4 digit address to read 220 COUNT 3 230 A 0 240 RETI 124 The Microcontroller Idea n n Book Displays 8 Displays In addition to switches and keypads for user input most projects also include a display to let users know what s going on inside The type of displa
81. you can run them But because the BASIC 52 language is so similar to the compilers you can do a lot of your testing with the interpreter and use the compiled version for final testing only There s also the added expense of buying the compiler But if you develop many different projects or if you need many copies of a single project the compiler can end up saving you money since you can use 8032 chips instead of the more expensive 8052 BASICs 246 The Microcontroller Idea Book Related Products Finally a compiled BASIC program usually requires more memory than an interpreted one but you do gain 8 kilobytes of code memory because you no longer need the BASIC 52 interpreter Programming Environments If you like the convenience of the BASIC 52 interpreter but would like features that make it easier to write edit and store your programs there are alternatives here as well MDL Labs and MicroFuture are two sources for development environments which are programs that typically include communications and program editing abilities Most run on IBM compatible host computers Figure 15 1 shows a typical screen The environments include features like these e Block editing or the ability to move delete or copy blocks of text in one operation e The ability to refer to subroutines by name rather than by line number 10 PRINT PORT 1 Bit Values 20 PRINT Bit O PORT1 AND 1 30 PRINT Bit 1 CPORTL AND 2 2
82. your program At any breakpoint you can view or change the contents of memory or perform other tests Simulators Another development tool is a simulator which is software that runs on a desktop computer and uses the video display to demonstrate what would happen if a specific microprocessor or microcontroller were to run a particular program You can look inside the simulated chip observe the contents of internal memory and single step or set break points to stop program execution at a desired program location or condition In this way you can get a program working properly before you commit it to EPROM One drawback to simulators is that they can t mimic all features of the chip of interest especially interrupt response and timing characteristics Emulators An in circuit emulator ICE is hardware that replaces the microprocessor in question by plugging into the microprocessor s socket on the device you want to test Like a simulator an emulator lets you control program execution and monitor what happens at each program step Microprocessor emulators typically are expensive AROM emulator is a lower cost option that simulates an EPROM using RAM for example for program storage and usually provides the abilities of a development system as well The 8052 BASIC s development system The 8052 BASIC system and a personal com puter form a complete development system for writing testing and storing programs The personal compute
83. 070h stores starting address of dptr vectortable vector table tokentable token table start address 10h first user defined token TGGP10 command or instruction name must use all capital letters beginning combination of letters must be unique 0 end of token indicator 11h 2nd user defined token SETP10 command or instruction name 0 end of token indicator 12h final user defined token CLRP10 command or instruction name Offh end of list indicator The Microcontroller Idea Book Calling Assembly language Routines Listing 13 7 page 2 of 2 can add up to 1Fh tokens final token must end with Offh org vectortable vector table address dw tggp10 label to branch to on TGGP10 command dw setp10 label to branch to on SETP10 command dw clrp10 label to branch to on CLRP1O command tggp10 org 3000h use any available address cpl pl o complement Port 1 bit 0 pin 1 ret return to BASTIC 52 setpl0 org 3010h use any available address setb p1 0 set Port 1 bit 0 pin 1 ret return to BASIC 52 clrp10 org 3020h use any available address clr pl o clear Port 1 bit 0 pin 1 ret return to BASIC 52 end The vector table consists of a list of labels corresponding to the beginning of each assembly language routine In addition to the tables you must store the assembly language routines themselves again using any free code data or code memory To use Listing 13 7 you must assemble it and up
84. 0h To verify that you re reading all bits correctly jumper each input in turn to ground and 5V and read the results Open inputs are undefined and may read as high or low To test U14 s outputs use this BASIC 52 statement XBY 0E400h xx where xx is the value you want to write to the chip To set all bits write 255 or OFFh To clear them write 0 To verify that all bits are responding connect a logic probe voltmeter or oscilloscope to each of the outputs of U14 in turn and verify that the bits respond correctly to your commands Input Examples Figure 6 3 shows some inputs that you can interface to U12 A TTL or CMOS logic outputs powered at 5 volts can directly drive U12 s inputs B To translate lower voltages to 5 volt logic use a 74HCT03 or similar open drain NAND gate with a pullup resistor to 5 volts C To translate higher voltages to 5 volt logic use a 74HC4050 buffer or 74HC4049 inverter powered at 5 volts These chips can safely accept inputs up to 15 volts D You can also detect the state open or closed of a toggle or slide switch at a port pin E An optocoupler is another way to interface different voltage levels and it also electrically isolates the input from the microcontroller circuit The Microcontroller Idea Book 93 Chapter 6 5V ANY TTL 7ALS244 OR CMOS ANY A TPUT PUT A 5V LOGIC ei LT 2V TO 5V 5V O 1 K ANY A INP
85. 1 off 0 40 usec C cursor on 1 off 0 B cursor blink on 1 off 0 Display curson 0 0 0 0 0 1 SC RL X X SE shift display 1 40 usec shift cursor 0 R L shift right 1 left 0 Functionset 0 0 0 O 1 DL N O X X DL 8 bit 1 4 bit 0 40 usec interface N dual 1 single 1 line display CG RAM 0 0 oO 1 CG5 CG4 CG3 CG2 CG1 CGO Load address counter 40 usec address set with CG0 CG5 Subsequent data goes to CG RAM DD RAM 0 Oo 1 DD6 DD5 DD4 DD3 DD2 DD1 DDO Load address counter 40 usec address set with DDO DD6 Subsequent data goes to DD RAM Busy Oo 1 BF AC6 AC5 AC4 AC3 AC2 AC1 ACO Read busy flag BF and 0 flag address address counter ACO counter read AC6 CG DD RAM 1 O D7 D6 D5 D4 D3 D2 D1 DO Write data DO D7 toCG 40 usec data write RAM or DD RAM CG DD RAM 1 1 D7 D6 D5 D4 D3 D2 D1 ODO Place data from CG 40 usec data read RAM or DD RAM on DO D7 X don t care 142 The Microcontroller Idea Book Displays Each character in the CG ROM and CG RAM has an 8 bit address or character code Conveniently the codes for the upper and lower case Roman alphabet and common punctuation are same as the ASCII codes for those characters 21h through 7Dh For example the pattern for A is stored at address 41h B is stored at at 42h and so on An 8 bit instruction register IR stores instruction codes and addresses and an 8 bit data register DR stores character codes When you read or write to the chip you must select
86. 1 0001 0011 20 0010 0000 0001 0100 29 0010 1001 0001 1101 30 0011 0000 0001 1110 99 1001 1001 0110 0011 178 The Microcontroller Idea Book Clocks and Calendars If you want an alarm frequency other than daily hourly or on the minute there are a couple of ways to achieve it For an alarm every 10 minutes you could generate an interrupt once per minute and ignore 9 out of 10 interrupts If this seems wasteful you can update the alarm minutes to the next desired value after each interrupt Using the example of an interrupt every 10 minutes you would set the mask bits for when minutes match 0 1 1 and start out by storing 0 in register 3 which will cause an interrupt to occur on the hour When the interrupt occurs you would add 10 to register 3 to schedule the next interrupt for 10 minutes after the hour By continuing to add 10 to register 3 after each interrupt and returning to 0 on a count of 60 you end up with an interrupt every 10 minutes As Table 10 1 shows many of the DS1286 s registers have multiple functions In register 9 bits 0 4 store the current month bit 6 enables the square wave output bit 7 enables the clock and bit 5 is always 0 For situations like this you can create mask bytes and use BASIC 52 s logical operators to read and write to selected bits while ignoring other bits in a register For example assume that you want to store a month in bits 0 4 of the 1286 s register 9 without affecting the settings o
87. 10 D ASC I GOSUB 800 420 D ASC N GOSUB 800 430 D ASC E GOSUB 800 440 D 20H GOSUB 800 450 D ASC 1 GOSUB 800 460 I 0C0H 470 GOSUB 900 480 D ASC L GOSUB 800 490 D ASC I GOSUB 800 500 D ASC N GOSUB 800 510 D ASC E GOSUB 800 520 D 20H GOSUB 800 530 D ASC 2 GOSUB 800 600 END 790 REM write data to the display 800 XBY X RS 1 810 XBY X RW 820 XBY A D 830 XBY X E 1 XBY X E 840 RETURN 890 REM write an instruction to the display 900 XBY X RS 910 XBY A I 920 XBY X E 1 XBY X E 930 RETURN The Microcontroller Idea Book 147 Chapter 8 Table 8 3 Initialization procedure for LCD modules using HD44780 controller Power on Wait 15 milliseconds after V 4 5V Function set 30h Wait 4 1 milliseconds Function set 30h Wait 100 microseconds Function set 30h Function set to match display module Display on Display clear Entry mode set set I equal to the instruction and call subroutine 900 which clears RS writes the instruction to the display and toggles E Using the example program as a model you can experiment with your own messages by adapting the code in lines 400 530 Listing 8 5 is another test program that displays a prompt on the host s screen and then displays the character you type at the keyboard both on the host s screen and on the LCD module To use this program you must add lines 10 through 380 of Listing 8 4 to initialize the module and variables T
88. 10 PORT1 PORT1 OR 3 REM set bits high to use as inputs 20 PRINT Please press switch P1 0 or P1 1 30 DO 40 A PORT1 AND 3 REM look at bits 0 and 1 only 50 UNTIL A lt 3 60 IF A 1 THEN S 1 70 IF A 2 THEN S 0 80 PRINT switch P1 S pressed 90 END The Microcontroller Idea Book 115 Chapter 7 8052 BASIC NORMALLY OPEN PUSHBUTTON a 1K 6 l Q P1 Q ete Figure 7 5 You can use a 74HC74 D type flip flop to latch a switch press A second port pin clears the flip flop Adding a Keypad Keypads offer more options than individual switches or pushbuttons but at lower cost and smaller size than a full keyboard Examples of products that may use keypads include electronic locks EPROM programmers and many test instruments On some devices the keys have custom legends that describe the specific functions of the keys but generic numbered keypads are also useful Keypad Types Some keypads have attached cables that terminate in a connector Others have headers to which you can solder wires or connect your own cable Different keypads follow different decoding schemes for detecting which key is pressed Some have a dedicated connector pin for each key and a single common pin to which the pins connect when a key is pressed Figure 7 6 You can wire and access these like a series of individual switches with a pull up or pull down resistor at each switch Other keypads use matrix encoding where the swi
89. 2 BASIC 39 po 1 K 1 K 10K 10K 10K 10K 10K 10K 5 O T2 ADO 1D 10 f 5V 1 T2EX ADI 2D 20 O PWM 2 PWM AD2 3D 30 i Rebecca cue ALEDIS 3 ALEDIS ADS 4D 40 LOW A U 4 PGM_PLS Apa 24 D4 13 sp 50 AQ A7 5 PGM EN ADS 6D 60 6 DMA ACK AD6 70 70 DI 7 LPT AD7 8D 80 u7 IN914 31 5V 11 6264 8K RESET EA O LE OR 1 30 Ta SER IN 2 P3 0 RXD ALE BASIC Hoc 2238 tee RESET rT 74HCIA 5 29 SER OUT P3 1 TXD PSEN cl P3 2 TNTO DMA J1 Q EXTERNAL ADDRESS LATCH AQ 1701 1OuF od 28 AIS 5 z Cy ALEDIS Al 1 02 P3 3 1NTI AIS U38 6 P3 4 T0 aa EZA 7 74HCTO8 A2 1 03 z P3 5 T1 A13 J A3 1704 WRITE gt P3 6 WR a2 ATI 1 aa 1705 READ P3 7 RD All U3A 3 AS 1706 AlO 74HCT 8 R DANY A6 1 07 XTAL2 AQ READ A7 1 08 XTALI A8 u a a MICROCONTROLLER 74HCT138 AD TE A All 23 a c2 Yo Al2 2 30 pF B Y1 H3 2000H Al2 Ld A Y2 H3 4000H RIV mes Y3 7 6000H ba zzi Y Hg 8200H J2 0 8K 26 6s YS fg AQQ0H o CS2 Al3 5V 4 gt Y6 C000H US 5 924 y7 Z E000H c4 MAX232 628 NC A14 T QuF Jay PART aT 0000H LO 8k en Cl veion ADDRESS DECODER o s 1 3 to 32K cl J3 27 c5 c7 HIGH ADDRESS BUS A8 A15 WRITE 2H WE 1 0uF 44 6 1 QuF 5V READ 221 0E C2 V 10V P 5 STATIC RAM c2 POWER AND GROUND PINS 13 R11 gt R10 12 RIO RS232 IN SER IN 330 4 re Tey2 GND 8 R21 R20 9 D N Ul 14 7 14 Ti0 tila c8 c9 C10 cll c12 c13 u2 40 20 RS232 OUT lt SER OUT By 1
90. 2 XI Y2 X2 Y2 X3 Y2 X4 Y3 XI Yog X2 YS XS Y3 X4 Y4 XI Y4 X2 Y4 X3 Y4 X4 0000m Tr rH rK VBIVWe9 O B S8SS SS SS SsO Row YIC1 18 oys ROW Y202 DATA OUT A ROW Y30 3 16 ODATA OUT B ROW Y404 5 ODATA OUT C LLATOROS5 140ODATA OUT D E MASKO 6 13 D OUTPUT ENABLE UMN X407 2ODATA AVAILABLE UMN X308 11 COLUMN X CND O9 HCOLUMN X2 74C922 16 KEY ENCODER A Q Q gri a i X2 Q l x3 Q 2 x4 Q Figure 7 8 Pinout truth table and waveforms for the 74C922 16 key encoder for matrix encoded keypads e Latches store the last keypress When you lift your finger from a key the keypad s X and Y lines no longer connect and there is no way to know that a key was pressed If the computer is busy doing something else while the key is pressed it may not see the keypress at all The 74C922 takes care of this by latching the data that corresponds to the last key pressed 120 The Microcontroller Idea Book Switches and Keypads e A single capacitor adds debouncing A capacitor connected at KBM keybounce mask sets the debounce period With a 1 microfarad capacitor the 74C922 ignores keypresses shorter than 10 milliseconds Only when a keypress lasts longer than this does the chip latch the data and bring DA high In a similar way after the key
91. 2 0883 407 724 3000 Hitachi America Ltd Semiconductor and IC Division Hitachi Plaza 2000 Sierra Point Parkway Brisbane CA 94005 1819 1 800 448 2244 Hosfelt Electronics Inc 2700 Sunset Boulevard Steubenville OH 43952 1158 1 800 524 6464 614 264 6464 Intel Corporation 3065 Bowers Ave Santa Clara CA 95051 408 765 8080 1 800 548 4725 Jameco 1355 Shoreway Road Belmont CA 94002 1 800 831 4242 415 592 8097 The Microcontroller Idea Book Sources products for wireless communications BASIC 52 development software display control chips HD44780 LCD controller data surplus components 8052 data book 8052 BASIC chip electronic components 257 Appendix A JDR Microdevices 2233 Samaritan Drive San Jose CA 95124 1 800 538 5000 408 559 1200 Lite On 720 S Hillview Dr Milpitas CA 95035 408 946 4873 L S Electronic Systems Design 2280 Camilla Rd Mississauga ON LSA 2J8 Canada 905 277 4893 Marlin Jones amp Associates P O Box 12685 Lake Park FL 33403 0685 407 848 8236 Maxim Integrated Products 120 San Gabriel Drive Sunnyvale CA 94086 408 737 7600 MDL Labs 1073 Limberlost Ct Columbus OH 43235 614 431 2675 Micro Computer Control P O Box 275 17 Model Avenue Hopewell NJ 08525 609 466 1751 Microcomputer Systems 1814 Ryder Drive Baton Rouge LA 70808 504 769 2154 258 electronic components infrared detectors 8051 programming book surplus components
92. 21 29 alarm circuit 178 184 ALE 21 29 ALEDIS 22 algorithms programming 56 Altair 8800 2 analog to digital converter 158 169 ASCII Hex format 223 assembly language defined 8 interfacing 217 238 B BASIC compilers 247 BASIC 52 booting 35 38 customizing 233 235 enhanced versions 245 246 in external memory 239 244 keywords 72 86 manuals 14 15 251 252 programming tips 65 71 running programs 39 40 source code 250 Basikit 247 BBS s 254 binary file format 223 numbers 272 books 251 253 bootup options 54 55 breakpoint 10 bus See address data C calendar functions 174 184 capacitors decoupling 30 chip choosing 5 6 clock real time 42 171 184 CMOS compatible logic 29 versus NMOS 6 code memory 21 88 COM port 36 command mode 66 companies 255 262 comparator 157 158 compilers defined 9 BASIC 246 247 computer host 3 15 16 construction materials 14 tips 31 32 CONTROL C 40 44 45 control circuits 185 198 CPU 17 crashes program 40 cross assembler 219 crystal accuracy 172 choosing 26 See also XTAL 57 DAC 227 228 data bus 27 data memory 21 debugging 9 10 37 70 71 decimal numbers 271 272 detector 153 development system 9 10 digital to analog converter 227 228 disk storage 63 64 displays 125 152 E EA 22 25 EEPROM 7 49 56 8051 family 1
93. 2C55 is greater current sourcing ability which can be important if you want to directly drive a transistor or source more than a fraction of a milliampere Intel s 82C55 can source 2 5 milliamperes at 3 volts compared to just 0 4 milliamperes at 2 4 volts for the 8255 However NEC s CMOS 71055 has the same current sourcing ability as the NMOS 8255 so it depends on the manufacturer All can sink 2 5 milliamperes at 0 45 volts The 74LS374 latch U14 has greater output drive ability than any of the 8255s Speed Ratings The 8255 is also available with different speed ratings including 3 Mhz and 5 Mhz The 5 Mhz part is sometimes called the 8255 5 From the ratings it may seem that the 8255 is too slow to interface to a 12 Mhz 8052 BASIC But what does the speed rating actually refer to Since the 8255 was developed for the 8085 I suspect that it refers to the maximum 82 C 55 PASO PA4 PA2 QO 2 PAS PALOS PAG PAQ O4 PA7 RODOS WR cs o6 RESET GND Q7 DO AIQ 8 D AQ QO D2 PC7 L410 D3 Pce 1 1 D4 PCS 2 D5 PC4 3 D6 PC U 14 D7 PC1 L415 VCC wey 6 PB7 POS ELL 7 PB6 PBO Q18 PB5 PBI 9 PB4 PB2 020 PBS Figure 6 5 Pinout of the 8255 Programmable Peripheral Interface The Microcontroller Idea Book 99 Chapter 6 Table 6 2 Pin functions for the 8255 Programmable Peripheral Interface Pin Symbol Input Function Output 1 PA3 1 0 Por A bit 3 2 PA2 VO Port A bit 2 3 PA1 V O Port A bit 1 4 PAO
94. 4 The Microcontroller Idea Book Microcontroller Basics makes sense For simpler designs a microcontroller with perhaps a keypad small display and solid state memory no disk drives can often do the job with less expense and smaller size In fact recently the two extremes have been meeting Some 32 bit microcontrollers are as capable as desktop systems and notebook size computers are available with solid state diskless storage Also expansion cards other hardware and software are now available for those who want to use desktop computers for monitoring and control tasks So there s something for everyone The 8052 BASIC chip described in this book is perfect for many simpler applications especially control and monitoring tasks Because the chip is easy to use it s a good way to learn about microcontrollers and computers in general Although you can t do the most complex projects with it you can do a lot at low cost and without a lot of hassle Designing and Building When you re ready to design and build the circuits for a project there are several ways to proceed You can design your circuits from scratch using manufacturers data books as guides you can follow a tested design a kit or project presented in a magazine for example or you can buy an assembled single board computer adding only the interfaces and programming your application requires This book presents designs that you can build yourself but you can a
95. 49 OR G gt 54 THEN END 9140 XBY 8000H G 9150 XBY 8001H INT RCAP2 256 9160 XBY 8002H RCAP2 XBY 8001H 256 9170 IF G lt 50 THEN END 9180 XBY 8003H INT MTOP 256 9190 XBY 8004H MTOP XBY 8003H 256 9200 END 9090 9130 prompt you to press a number from 1 to 6 to simulate a PROG1 PROG6 command or to press Q to quit Lines 9140 9190 store the PROG value 1 6 RCAP2 for saving the baud rate and MTOP as requested Listing 14 2 stores only the current program not multiple programs like the PROG com mand But you can store a new program whenever you wish by writing over the previously stored program And you don t have to worry about removing and erasing an EPROM when it s filled If you have a 32K RAM at 0 remember to set MTOP to 7FFFh and use Listing 14 2 to execute a PROG3 to ensure that your NV RAM won t be overwritten on bootup You can use EEPROM with Listing 14 2 if you add a delay loop after each write operation using XBY as described for Listing 14 1 244 The Microcontroller Idea Book Related Products 15 Related Products Because of the popularity of the 8052 BASIC chip many companies have developed products to simplify the tasks of designing building and testing BASIC 52 systems This chapter describes some of the offerings in these areas Enhanced BASIC 52 The BASIC 52 interpreter contained in the original 8052 BASIC is a good full featured and easy to use programming lang
96. 5 16 8052 BASIC about 11 26 NMOS versus CMOS 6 8255 98 108 Index embedded controller emulator 10 environments programming 247 248 EPROM about 6 7 adding 56 60 programming 236 238 testing programs in 9 erasing NVRAM EEPROM 55 errors finding program 9 10 70 71 executable file 219 external memory accessing 21 22 42 circuits 25 29 F Flash EPROM 7 formats file 222 224 FPROG using 53 55 circuits 60 61 simulating 243 244 G gain control op amp 189 191 GET 44 45 H HEX2RAM BAS 264 265 hexadecimal numbers 70 272 273 HEXLOAD BAS 266 269 history of microcomputers 2 3 host computer 3 I T O ports adding 89 108 in 8052 20 22 Port 1 40 41 infrared 199 215 275 Index Input Output see I O instruction set 6 Intel Hex format 220 224 interface chips 98 interfacing to a port 93 96 interpreters 9 interrupts assembly language 232 233 in 8052 22 types 112 114 K keypad 116 124 keywords BASIC 52 72 86 defined 65 kilobyte 273 L languages programming 8 9 latch octal transparent 26 27 LCD 135 152 LED 125 135 lenses 215 216 level translating analog 167 168 digital 93 96 light emitting diode 125 135 liquid crystal display 135 152 logic families 29 20 unused gates 34 M machine code 8 manuals 14 15 matrix switch 187 189 Megabyte 2
97. 5 to 6V 15 milliwatts e What input modes are available single ended differential pseudo differential e How is the converter controlled and interfaced control signals are WE OE CS e Are there any special features on chip sample and hold voltage reference etc an internal clock times the conversions e What package types are available 24 pin 0 3 DIP 28 lead chip carrier Sample and Hold Circuits An additional component that you may need for rapidly changing analog inputs is a sample and hold circuit To ensure correct conversions the analog input must not change in value while the conversion is taking place A sample and hold circuit ensures that the analog signal is stable by sampling the signal at the desired measurement time and storing it usually as a charge on a capacitor The converter uses this stored signal as the input to be converted When do you need a sample and hold The ADC0848 requires 60 microseconds or less to convert so you should get good results with inputs that do not vary more than 1 bit in this amount of time When a rapidly changing input does require one sample and hold ICs like the LF398 are available or you can use a converter like the ADC0820 which has the sample and hold on chip The Microcontroller Idea Book 169 170 The Microcontroller Idea Book Clocks and Calendars 10 Clocks and Calendars Many 8052 BASIC systems can make use of a real time clock that keeps track of second
98. 5V typical switch resistance is 120 ohms at 12V it drops to 45 ohms This should cause no problems in switching standard LSTTL or CMOS signals If you are routing an analog voltage to a low impedance input the switch resistance may attenuate the signal Maximum switching frequency of the chip is 20 Megahertz In Figure 11 2 the switch array is controlled by Port A and bit 7 of Port C PC 7 on an 82C55 PPI Bringing PC 7 high opens all of the switches If you don t need this ability you can tie RESET low and use PC 7 for something else You can use any output port bits to control the MT8808 Logic high inputs at the MT8808 must be at least 3 5V though so if you use NMOS or TTL outputs add a 10K pull up resistor from each output to 5V For a simple test of the switches you can connect a series of equal resistors as shown to the X inputs Each X input will then be at a different voltage To verify a switch closure measure the voltages at the selected X and Y inputs they should match 820535 MT8808 8X8 SWITCH ARRAY pao li 24l AXo PAL 25 aX yes PA2 2 26 ax9 y HZ pa3 H 27l avg y2H6 pag 2 28 Ay yH PAs P29 Lay y44 pas AIDATA y5sH pa7 PZ 21S TROBE vers pc7 H2 LOIRESET ea VDDVEEVSS X X1X2 X3 X4 X5 X6 X7 ite a g gi re PPI ay Ge FRE 5V CONNECT 10K RESISTORS FOR TESTING Figure 11 2 With the MT8808 switch array an 8 bit output port can connect eight X inputs to eight Y inputs in a
99. 6 DQl DQ5 DQ2 DQ4 GND DQ3 8K X 8 EEPROM Figure 4 2 Pinout for8K EEPROM commands verify each byte after programming it so the inverted data automatically keeps BASIC 52 from programming another byte until the EEPROM is ready to receive it Other EEPROMs have a busy output usually at pin 1 which goes low when the EEPROM is busy For this type you can tie the busy output to pin 12 of U1 BASIC 52 s programming commands wait for a high logic level at this pin after programming each byte Note that this means that pin 12 of the 8052 BASIC must be high or not connected during programming of any device However using the BUSY output is optional since program ming won t continue until the programmed byte verifies Whether you choose EEPROM or NVRAM be sure to ask for a data sheet for the device you buy so you can verify its pinout capacity and timing characteristics Adding NVRAM or EEPROM Figure 4 3 shows the added circuits for the NVRAM or EEPROM at U8 Because the circuits are an addition to Figure 3 1 s circuits the parts continue the same numbering sequence beginning with U8 AND gate U3C is the third gate of Figure 3 1 s U3 Table 4 1 is a parts list of the components needed to add Figure 4 3 s circuits to Figure 3 1 50 The Microcontroller Idea Book Saving Programs DATA BUS D D7 U8 LOW ADDRESS BUS DS1225 8K NVRAM AQ A7 OR 2864 8K EEPROM HIGH ADDRESS BUS DO A8 A15 D6 eee NO CON
100. 64 8K EPROM Once again the pin functions and locations are similar to those in an 8K RAM During normal operation the data pins DQ0 DQ7 are read only Pin 27 which is Write Enable WE on RAM is PGM or program pulse on the EPROM and pin 1 which has no connection on RAM is VPP or programming voltage on the EPROM EPROM programming Circuits Figure 4 5 shows additions to Figure 4 3 s circuits that enable you to program a 12 5V 8K EPROM instead of NVRAM or EEPROM Table 4 2 is a parts list for Figure 4 5 s circuits The Microcontroller Idea Book 57 Chapter 4 2764 27C64 Vpp l Vcc Al2 2 PGM A7 3 NC A6 4 A8 A5 5 AQ A4 6 All A3 7 OE A2 8 Al Al 9 CE A l DQ7 DQ l DQ6 DQ l DQ5 DQ2 l DQ4 GND l DQS 8K X 8 EPROM Figure 4 4 Pinout for 8K EPROM The components continue the numbering sequence begun in Figures 3 1 and 4 4 The additional circuits for the PROG commands are at pin 1 of U8 Jumper J5 allows you to configure the memory site for the type of NV memory you re using On NVRAM or EEPROM pin 1 has no connection or on some EEPROMs it s a BUSY output On the EPROM it s VPP which is 5V during read operations and 12 5V during programming PGM EN pin 6 on the 8052 BASIC controls the programming voltage by going low during programming operations and otherwise remaining high To prevent accidental programming during power up OR gate U10A s output remains high until RESET goes low U10 is no
101. 73 memory accessing external 20 22 42 check 38 decoding 91 91 8052 s 6 map 87 89 mercury switch 155 microcontroller defined 1 276 microprocessor 2 mnemonics 8 modules program 66 67 motor control 191 198 MTOP 38 53 55 multiplexed address data bus 20 N NMOS compatible logic 29 versus CMOS 6 nonvolatile memory 47 61 number systems 271 272 NVRAM 48 56 O object file 219 OE 29 on off switch 33 op amp gain control 189 191 orientation component 32 33 oscillator design 203 See also crystal XTAL output enable 29 pe boards 248 249 PGM EN 22 58 60 PGM PULSE 22 52 photocell 157 port See I O Port 1 40 41 power supply connections 22 PROG commands about 53 60 simulating 243 244 programmable peripheral interface 98 108 program assembly language 217 238 crashes 231 documenting 67 exiting 44 45 saving 47 64 storage 6 7 program enable 22 58 60 program pulse 22 52 program status word 231 program store enable 21 26 programming commands 22 53 60 environments 247 248 languages 8 9 tips 66 68 PSEN 21 26 psw 231 PWM 195 198 R radio link 216 RAM choices 28 29 in 8052 20 use 7 RD 21 26 RDANY 26 read cycle 29 of port 96 97 signal 21 references 14 15 relay 187 189 reserved words EPROM programming 61 62 defined 65 for 8052 BASIC 14 system 30 wireless
102. 74HCT32 INPUT BUFFER i tee T KEY PAL Ou C2 INTE lt oe 74C922 ANY R n es 16 KEY ENCODER Figure 7 9 Circuits for adding a matrix encoded keypad to an 8052 BASIC system The Microcontroller Idea Book 121 Chapter 7 A 1 microfarad capacitor at KBM and 0 1 microfarad capacitor at OSC give a keyboard debounce of 10 milliseconds and a scan rate of around 600 hertz Larger values will increase the debounce time and decrease the scan rate The 74C922 s data sheet recommends choosing KBM s capacitor to be ten times the values of OSC s capacitor so be sure to change both if you change either Testing the Keypad Listing 7 3 tests Figure 4 s circuit The program waits for a key press and when one occurs displays the value of the key on the host computer The following paragraphs explain the program in greater detail Lines 10 25 are a lookup table that translates the 74C922 s A D outputs into an ASCII code corresponding to the key pressed The table is stored at locations 1 FFOh 1FFFh in external RAM The lookup table is arranged with the values of the 74C922 s data outputs 0 Fh in ascending order Notice that the key legends 0 F do not follow in order in the table because the legends on the keypad correspond to the data outputs only at keys 4 6 and F Lines 30 50 are the main program loop This does nothing except wait for an interrupt When you press a key the 74C922 s DA output goes high The falling
103. 8052 BASIC Programs in BASIC 52 and assembly language cause a sine wave to appear at the converter s output There s also a section on how to use your BASIC 52 system as a general purpose The Microcontroller Idea Book 217 Chapter 13 EPROM programmer for storing assembly language routines or anything else you want to program into an EPROM for use on an 8052 BASIC system or another device Assembly language Basics The bare 8052 chip understands just one language the binary machine codes that make up the chip s instruction set The 8052 s data book describes the function of each of the machine codes You can of course write programs without having to look up binary codes by using a programming language The language that is closest to the machine codes is assembly language where a mnemonic or abbreviation represents each of the codes The assembly language program that you write is called a source file After you write a source file you must use an assembler to translate the source file into an object file which contains the machine codes that the chip will execute You also must have a way of storing the object file in the 8052 BASIC system s memory where the 8052 BASIC chip can access it The BASIC 52 interpreter is itself an assembled program that the 8052 runs on boot up The interpreter reads your BASIC 52 programs from memory and translates them into machine codes for the 8052 to execute It does the same for the
104. 8052 BASIC system you have to ensure that BASIC 52 has enough time to process each line before the next one arrives If there isn t enough time you ll have missing characters or lines in uploaded programs There are a couple of ways to ensure that your uploads are complete Most software allows you to add delays after each transmitted line or character You can experiment with different values to find the shortest delays that allow you to upload reliably If you keep your program lines short the delays between lines can be shorter If these options aren t available try using a slower baud rate which gives BASIC 52 a little more time to process each line before the next one arrives Downloading to the Host Computer To download a BASIC 52 program from the target s RAM to the host s disk type LIST to list the current program but before you press ENTER to execute the command set up your host s software to download or receive an ASCII file When prompted specify a filename When the transfer is ready to go press ENTER to send your program to the host When you see the READY prompt end the transfer by whatever means your software requires In Procomm Plus press ESCAPE You should now have a file on disk containing the program you just listed You can test your download by erasing the program in the 8052 BASIC system s RAM and then uploading it back into RAM The Microcontroller Idea Book 63 Chapter 4 First type N
105. 876 401 762 9000 Basicon Inc 14273 NW Science Park Drive Portland OR 97229 503 626 1012 The Microcontroller Idea Book stepper motors motor control chips surplus components 8051 assembler 8051 assembler LCD modules manual publication 238 80C52 BASIC chip systems related products 255 Appendix A Binary Technology PO Box 67 Meriden NH 03770 603 469 3232 Blue Earth Research 165 W Lind Ct Mankato MN 56001 507 387 4001 Blue Ridge Micros 2505 Plymouth Road Johnson City TN 37601 615 335 6696 Dallas Semiconductor 4350 South Beltwood Parkway Dallas TX 75244 3292 214 450 0400 1 800 336 6933 Digi Key Corporation 701 Brooks Ave South P O Box 677 Thief River Falls MN 56701 0677 1 800 344 4539 Dunfield Development Systems P O Box 31044 Nepean Ontario K2B 8S8 Canada 613 256 5820 Edmund Scientific Company 101 E Gloucester Pike Barrington N J 08007 1380 609 573 6250 256 BASIC compiler 8052 BASIC systems related products 8052 BASIC systems related products 8052 BASIC board NV RAM real time clocks electronic components 8051 assembler lenses optical components other scientific equipment The Microcontroller Idea Book Electronics 123 17921 Rowland Street City of Industry CA 91748 1 800 669 4406 818 913 6735 F C Kuechmann 8113 NE 25th Ave Vancouver WA 98665 Harris Semiconductor P O Box 883 Melbourne FL 3290
106. AN PCON PWM Logical Operators RCAP2 RETI AND T2CON OR TCON XOR TIME TIMERO Assembly language Interfacing TIMER1 TIMER2 CALL TMOD LIST PHO PH1 PRINT P UIO UIl UOO UO1 The Microcontroller Idea Book 73 Chapter 5 Quick Reference to BASIC 52 This quick reference to the BASIC 52 programming language lists the keywords alphabeti cally along with brief descriptions of function and use Conventions The reference uses the following typographic conventions KEYWORDS boldface uppercase BASIC 52 keywords placeholders italics Variables expressions constants or other information that you must supply optional items enclosed in square brackets Items that are not required repeating elements followed by ellipsis three dots You may add more items with the same form as the preceding item C command mode R run mode variable expression C R Assigns a value to a variable expression expression C R Equivalence test relational operator expression expression C R Add expression expression C R Subtract expression expression C R Multiply 74 The Microcontroller Idea Book Programming expression expression C R Divide expression expression C R Raises first expression to value of second expression exponent expression lt gt expression C R Inequality test relational operator expression lt expression C R Less than test relational operator
107. AND 80H 80H Or in more general terms use this format A XBY address AND 2 bit 2 bit 110 The Microcontroller Idea Book Switches and Keypads 5V 10K PULLUPS ANY 8 BIT INPUT PORT BIT SWITCH A BIT 1 SWITCH B BIT 2 SWITCH C BIT 3 SWITCH D BIT 4 SWITCH E BIT 5 SWITCH F BIT 6 SWITCH G BIT 7 SWITCH H INPUT BIT MEANS SWITCH IS SELECTED Figure 7 2 Usea rotary switch to allow users to choose from among several options where address is the location of the byte to be read in memory and bit is the bit number of the switch Detecting a Switch Press Momentary switches are useful when you want to get the computer s attention For example you might have a program that normally displays the current temperature and time but switches to a setup routine when you press a switch On a normally open pushbutton momentary switch the contacts close when you press the switch then open as you release it In a normally closed momentary switch the contacts open when you press and close on release Using Interrupts An easy way to detect a switch press is with an external interrupt The 8052 BASIC automatically detects the switch press and branches to an interrupt handling subroutine The Microcontroller Idea Book 111 Chapter 7 Listing 7 1 Displays a message when external interrupt 1 is detected 10 ONEX1 100 20 DO 30 WHILE 1 1 40 END
108. BASIC 52 commands that you type at the keyboard The interpreter program includes many modular routines that BASIC 52 uses such as reading a character from the serial port or comparing two values BASIC 52 programs are slow for two reasons One is that the interpreter must translate each line of code every time it executes it With assembly language the assembler translates the program only once and the 8052 then reads and executes the binary codes directly from memory The other reason for the slowness of BASIC 52 programs is that the nterpreter program s translation from BASIC 52 to machine code doesn t result in the most efficient code Programming directly in assembly language gives you much greater control over the final code that the 8052 will execute Incidentally assembly language isn t the only way to get faster execution times Other options include using a BASIC or C compiler or using a faster crystal to clock the 8052 But as arule these approaches will not speed up programs as dramatically as assembly language What You Need To add assembly language routines to your BASIC 52 programs you need several items a programming reference with details about the 8052 s assembly language a text editor for writing the source files an assembler to create the executable files memory in the 8052 BASIC system for storing your programs and a way to transfer your executable files 218 The Microcontroller Idea Book Calling Assembly l
109. D1 is essentially the same as U1 s DATA OUT in Figure 12 1 but inverted USA inverts MOD1 s output so that pin 9 of U4 matches U1 s DATA OUT You can substitute just about any CMOS inverter The decoder chip U4 requires timing components to match U1L s oscillator frequency R9 and C7 set the timing that discriminates between narrow and wide received pulses R10 and C8 set the timing that detects the end of an encoded word and the end of a transmission Figure 12 2 shows Motorola s formulas and recommendations for choosing these values U4 has five address lines A1 A5 which must match A1 A5 on U1 As with U1 the inputs are trinary and may be logic high logic low or open For testing you can set these with jumpers or switches When MOD transmits U4 examines the incoming bits at its pin 9 If the five address bits received match U4 s address U4 stores the next four bits and compares them to the previous four data bits received If the data bits don t match D6 D9 don t change If the data bits do match the receiver latches the new data to D6 D9 and brings VT pin 11 high to indicate that a valid transmission was received The receiver doesn t latch D6 D9 until it receives the same data twice in a row This complements the behavior of U1 which automatically sends each transmission twice Requiring the receiver to see the same data twice prevents the receiver from accepting data that was garbled in transmitting The only
110. EPROM EEPROM or NV RAM with the buffer s contents If you don t have an adapter you can use the technique described above to copy BASIC 52 into NV RAM or EEPROM and then read the device into your programmer To read a DS1225 into an EPROM programmer s buffer configure the programmer for a DS1225 or 2764 EPROM since the pinouts for reading these devices are the same Place the DS1225 in the programming socket and read the contents into the programmer s buffer Be sure not to subject the DS1225 to any EPROM programming voltages by trying to program the device as an EPROM for example since this could be lethal to it After reading the DS 1225 insert a 2764 EPROM into the programming socket and program the EPROM with the buffer s contents You now have an EPROM with the same contents as your NV RAM System Requirements To run BASIC 52 from external memory your circuit must include the following e Any 8052 8032 80C52 or 80C32 chip with pin 31 tied low e BASIC 52 stored in non volatile memory NVRAM EEPROM or EPROM beginning at 0 in code memory e At least 1K of read write memory RAM beginning at 0 in data memory required for all BASIC 52 systems e For permanent storage of BASIC 52 programs non volatile memory beginning at 8000h in data or code data memory One limitation to running BASIC 52 from external memory is that you can t use PROG FPROG or PGM This is because during programming BASIC 52 acc
111. ET COMPUTER PC 8052 BASIC Figure 3 5 Pin connections for 25 pin and 9 pin RS 232 connectors e Don t plug the ICs into their sockets until you ve completed wiring all of the circuits Unused Gates Two gates on U3 and five gates on U1 are unused To prevent the unused CMOS inputs from floating and possibly drawing excessive currents wire pins 9 10 12 and 13 of U3 to ground or 5V Do the same for pins 3 5 9 11 and 13 of U1 Don t forget to remove these connections if you later use the pins If you are using LSTTL chips 74LS08 74LS 14 leave the unused inputs open 34 Tne Microcontroller Idea Book Powering Up Serial Connectors Connections to RS 232 OUT and RS 232 IN depend on the type of serial connector you have on your personal computer or its serial cable Connectors vary but two common ones are a male 25 pin or 9 pin D connector The outer shell of a D connector is roughly in the shape of a D For the 8052 BASIC system you ll need a mating female 25 pin or 9 pin D connector The connection has just three wires A solder cup type connector allows easy soldering of the wires Figure 3 5 shows the wiring for 9 and 25 pin connectors A few computers require additional handshaking signals BASIC 52 doesn t support these but you can simulate them by connecting together pins 5 6 8 and 20 at the personal computer end of the link Pin numbers are for a 25 pin connector Powering Up The first time
112. EW to erase the program To restore your program by uploading it from disk set up your host s software to upload or send an ASCH file and enter the name of your previously downloaded file As the file loads you ll see each program line on screen The file will contain a READY prompt after the program listing This causes BASIC 52 to display an error message which you can ignore Type LIST to view the uploaded program and type RUN to run it With BASIC 52 programs on disk you can use any text editor to view or modify the program Save the file as pure ASCII text with no formatting commands added You can also use your text editor to create a program from scratch then upload it to BASIC 52 rather than typing the lines using BASIC 52 s line editor 64 The Microcontroller Idea Book Programming 5 Programming When you have your 8052 BASIC system up and running yov re ready to start writing and running your own programs This chapter is an introduction to the BASIC 52 programming language It includes a summary of BASIC 52 s abilities some examples that illustrate what you can do with it plus tips for writing and debugging programs For a complete reference to BASIC 52 see the BASIC 52 programming manual either version which includes many more examples and details about the language and how it works You can learn a lot about BASIC 52 by browsing through the programming manual and experimenting on your own Programmin
113. HO be sure to include the period and use a zero not the letter O Crystal Frequency The special operator XTAL represents the value of the timing crystal that clocks the 8052 BASIC The default value is 11059200 or 11 0592 Mhz You can verify this by typing PRINT XTAL Most BASIC 52 statements don t use the XTAL operator so it doesn t matter if the value isn t accurate Exceptions are the real time clock programming commands PWM output and LPT output For these XTAL should match your crystal s frequency To set XTAL for a 12Mhz crystal type XTAL 12000000 To verify type 38 The Microcontroller Idea Book Powering Up PRINT XTAL Line Editing After typing a few commands you may discover some of BASIC 52 s line editing abilities While typing a line you can correct mistakes by deleting back to the mistake and retyping In Procomm Plus if you select VT100 terminal emulation under Setup menu Terminal Options you can use either the DELETE or BACKSPACE key to delete With the Windows terminal you must use the DELETE key not BACKSPACE Many communications programs allow you remap the keyboard so you can select whatever delete key you wish Once you press ENTER you can t edit a line you ve typed unless you retype it from the beginning BASIC 52 treats upper and lower case characters the same In most cases spaces are ignored so you can include them or not as you wish Running a Program He
114. IS are high During normal memory accesses ALEDIS remains high and ALE controls U4 ALEDIS disables the latches when BASIC 52 executes its programming commands Figure 3 1 s circuit doesn t use the programming commands so ALE could control U4 directly but again I ve included U3B for future use Because ADO AD7 hold the data to be read or written during a memory access the signals as a group carry the label DATA BUS Each line of ADO AD7 has a 10K pullup resistor These are The Microcontroller Idea Book 27 Chapter 3 required for the programming functions and are included for future use You can use eight individual resistors or aresistor network that contains eight resistors ina SIP or DIP package In a bussed resistor network one pin connects to one side of all of the resistors so you have fewer connections to wire The remaining bus is the HIGH ADDRESS BUS A8 A15 which consists of the upper eight address lines and is not multiplexed Address decoding U6 is a 74HCT138 3 to 8 line decoder It functions as an address decoder for the 64K external memory space Address decoding allows multiple chips to connect to the address and data buses with each chip enabled only when it is selected Figure 3 2 shows a truth table for the decoder The 8052 BASIC chip uses the three highest address lines A13 A15 to generate a chip select signal for each of eight 8K blocks in memory This is by no means the only way to decode memory bu
115. ND gate that combines the encoder s output and the 40 kilohertz oscillator in Figures 12 1 and 12 5 Series drive A simple way to double the power is to use two IREDs in series as Figure 12 8A shows With about 1 7 volts across each IRED the series combination drops 3 4 volts Instead of wasting energy by dropping 3 volts across a resistor more of the current does useful work by powering a second IRED The maximum possible current through the IREDs is determined by the transistor s base current and gain Outputs in the 74HC logic family can sink up to 25 milliamperes absolute maximum and are a good choice for driving the base Resistor R2 controls the amount of current through the IREDs To determine a safe current through an IRED you need to know the specifications of the IRED you are using as well as how you plan to use the IRED in your circuit The data sheet for any IRED should include an absolute maximum rating for continuous current This is the maximum current that the device can withstand without damage For example for Harris F5D1 this value is 100 milliamperes When the IRED is powered continuously the current through it shouldn t exceed this value Since this is an absolute maximum it s a good idea to stay well below it The infrared transmitter doesn t require the IRED to be on continuously however Instead it pulses the IRED at 40 kilohertz In non continuous or pulsed operation the IRED can handle much gre
116. NECTION 8000H 5V 3 O RESET 2 74HCT32 C14 5V lyr O J4 6 WRITE PROTECT 9 WRITE 3c 3 K PGM PULSE POWER AND GROUND PINS R DANY U8 28 l U9 14 7 Figure 4 3 Circuits for adding NVRAM or EEPROM The pinout and wiring of U8 are similar to that of the RAM at U7 The data and address lines are wired exactly the same as for U7 U8 is accessed from 8000h to 9FFFh This location is used because BASIC 52 s programming commands assume that the nonvolatile memory begins at 8000h OR gate U9A prevents the NVRAM or EEPROM from being accidentally overwritten during power up When the 8052 BASIC first powers up its port pins are in an unknown state for a brief period until the reset algorithm in the chip brings them all high During this The Microcontroller Idea Book 51 Chapter 4 Table 4 1 Parts list for Figure 4 3 Semiconductors U8 8 kilobyte NV memory DS1225 NVRAM or DS1213 SmartSocket with 6264 SRAM or 2864 EEPROM access time 250 nanoseconds or less U9 74HCT32 quad OR gate Capacitors 16WVDC 20 tolerance C14 0 1 microfarad ceramic disc Miscellaneous J4 SIP header 3 terminal and shorting block IC sockets time there is a small chance that the right combination of outputs will cause a write operation to occur at U8 Since this could destroy the information stored in the chip we need a way to prevent U8 from being written to for a brief time after power up OR gate U9A prevents acc
117. PUT Seconds 0 59 S 250 REM initialize clock to current seconds 260 TIME S 270 REM start clock 280 CLOCK 1 290 RETURN 500 REM increment and display time once per minute 510 REM reset seconds 520 TIME 0 530 REM increment minutes 540 M M 1 550 IF M 60 THEN GOSUB 700 560 REM display current time 570 PRINT the time is 580 PRINT H hours 590 PRINT M minutes 600 IF AP 0 THEN PRINT AM ELSE PRINT PM 610 RETI 700 REM once hour timekeeping 710 REM reset minutes 720 M 0 730 REM increment hours 740 H H 1 750 REM at 12 00 toggle am pm 760 IF H 12 THEN AP A 770 REM at 1 00 reset hours 780 IF H 13 THEN H 1 790 RETURN The Microcontroller Idea Book 173 Chapter 10 Listing 10 2 Toggles a port bit and displays the result 10 REM toggles P1 7 once per second 20 TIME 0 30 CLOCK 1 40 DO 50 ONTIME 1 100 60 WHILE 1 1 70 END 100 REM reset time 110 TIME 0 120 REM toggle Port 1 bit 7 130 PORT1I PORT1 XOR 80H 140 PRINT Port 1 bit 7 PORT1 AND 80H 80H 150 RETI But in reality because of the way that BASIC 52 calculates time small variations in XTAL usually do not effect the real time clock Although BASIC 52 will store a XTAL value as precise as 12000001 it uses the same time base for all XTAL values from 11963191 to 12039877 If your crystal frequency is within this range small adjustments to XTAL won t make the real time clock more accurate The value
118. QuF O luF O 1uF O 1uF O luF 0 1uF U3 14 7 7 120 T21 10 by En u4 20 10 us 16 15 U6 16 8 RS232 INTERFACE PLACE A 1uF CAPACITOR NEAR THE 5V AND u7 28 GND CONNECTIONS OF EACH IC Figure 3 1 Complete 8052 BASIC system for experimenting The Microcontroller Idea Book 24 Powering Up Table 3 1 Parts list for Figure 3 1 s circuit Semiconductors LED1 Light emitting diode Ul 74HC14 quad inverting Schmitt trigger U2 8052 BASIC or 80C52 BASIC microcontroller U3 74HCTO08 quad AND gate U4 74HCT373 octal transparent latch U5 MAX232 RS 232 driver receiver U6 74HCT138 3 to 8 line decoder U7 6264 8 kilobyte or 62256 32 kilobyte static RAM access time 250ns or less Resistors 1 4 watt 5 tolerance R1 R9 10 000 ohm R10 330 ohm Capacitors 16WVDC 20 tolerance C1 C8 10 microfarad aluminum or tantalum electrolytic C2 C3 30 picofarad ceramic disc C4 C7 1 0 microfarad aluminum or tantalum electrolytic C9 C13 0 1 microfarad ceramic disc Miscellaneous J1 J3 SIP header 3 terminal and shorting block Sl Switch normally open momentary pushbutton XTALI 11 0592 Mhz crystal RS232 connector IC sockets perforated board wire solder and other circuit construction materials The Microcontroller U2 is the 8052 BASIC chip The circuit is designed so that you can use either the NMOS version or the CMOS 80C52 BASIC EA the External Access Enable input pin 31 of U2 connects to
119. R Figure 11 4 The UCN5804B makes it easy to control the speed direction and operating mode of a stepper motor 8052 BASIC to do other things without having to worry about generating the signals to control each step of the rotation The circuit uses a UCN5804B stepper motor translator driver U5 from Allegro Microsys tems formerly Sprague The chip automatically creates the drive signals for operation in any of three modes U3 is a4066B CMOS quad switch that enables you to select any of 15 speeds U4 is a 555 timer that outputs a square wave in proportion to the selected speed U5 uses the square wave to time the steps US has four outputs that can sink up to 1 5 ampere each and can sustain up to 35 volts The chip includes diodes that protect against inductive transients and thermal protection that 192 The Microcontroller Idea Book Control Circuits disables the outputs if the chip begins to overheat For high output currents use a slide on DIP heat sink to prevent overheating The motor is a 4 phase unipolar type This type of motor has six leads that connect to two sets of coils with two coils in each set Surplus motors often don t include complete documentation but you can sort out the leads with an ohmmeter and some experimenting Begin by looking for a lead that measures an equal resistance typically 5 to 50 ohms to two of the other leads Wire this lead to 5 V and pin 2 of U5 Wire the two leads that conn
120. RETURN The Microcontroller Idea Book 149 Chapter 8 Listing 8 6 page 1 of 2 Creates and displays a custom character upside down question mark on an LCD module REM You must add lines 5 380 from Listing 8 4 to this 2 REM program 400 REM R1 R8 store row patterns for custom character 401 R1 4 402 R2 0 403 R3 4 404 R4 8 405 R5 10H 406 R6 11H 407 R7 0BH 408 R8 0 410 REM custom character number 420 CC 0 430 XBY X RS 440 XBY X RW 450 REM display clear 460 XBY A 1 470 XBY X E 1 XBY X E 480 REM set CG RAM address to 0 490 XBY A 40H 500 XBY X E 1 XBY X E 510 REM store R1 R8 in CG RAM 520 D CC R1 530 GOSUB 800 540 D CC R2 550 GOSUB 800 560 D CC R3 570 GOSUB 800 580 D CC R4 590 GOSUB 800 600 D CC R5 610 GOSUB 800 620 D CC R6 630 GOSUB 800 640 D CC R7 650 GOSUB 800 660 D CC R8 670 GOSUB 800 150 The Microcontroller Idea Book Displays Listing 8 6 page 2 of 2 680 XBY X RS 690 XBY X RW 700 REM set DD RAM address to 0 710 XBY A 80H 720 XBY X E 1 XBY X E 730 XBY X RS 1 740 REM write custom character 0 to display 750 XBY A 0 760 XBY X E 1 XBY X E 770 END 790 REM write data to display 800 XBY X RS 1 805 XBY X RW 810 XBY A D 820 XBY X E 1 XBY X E 840 RETURN 890 REM write an instruction to the display 900 XBY X RS 910 XBY A I 920 XBY X E 1 XBY X E 930 RETURN With a 4 bit interface you have two e
121. RRUPT A OUT INTACI ae 28 O VCC 5V m NCO2 27 OWE WRITE ENABLE NO CONNECTION NC O3 26 O INTB INTB INTERRUPT B OUT NC O4 25 ONC 7 tee SANG _ NO CONNECTION A4 g6 230 SQW SQUARE WAVE OUT ADDRESS INPUTS A3 07 22 D0E OUTPUT ENABLE A2 08 21 DOPEN PIN MISSING Algo 20 DOCE CHIP ENABLE L Aogio 190DQ07 F m pao 18 ODQ6 DATA 1 0 DOI 2 DAs DATA 1 0 C porurs 16 Da4 GROUND GND O14 ISO Das 2 DS1286 WATCHDOG TIMEKEEPER Figure 10 1 Pinout of the DS1286 Watchdog Timekeeper The DS1286 contains a series of registers that store time date alarm and configuration information You can read the current time and date from the DS1286 in hundredths of seconds seconds minutes hours day of the week date of the month and year Months of different lengths and even leap years are handled automatically Clock accuracy is better than 1 minute per month at 25 degrees Celsius Figure 10 2 shows the pin connections for a DS1286 in a BASIC 52 system To accommo date its crystal and power source the DS1286 a 28 pin encapsulated DIP just like the one used by Dallas NVRAMs The pinout and wiring are similar to that for static RAM The chip s access time is 150 nanoseconds which is well within the 8052 BASIC s timing requirements The eight data lines DQO DQ7 connect to the data bus The chip has just six address inputs A0 A5 which are all it needs to access its 64 bytes The clock calendar uses 14 bytes and 50 bytes of
122. SMISSION RECEIVED TIMING COMPONENT CALCULATIONS ROI C7 3 95 R1 C2 R1 C8 77 R1 C2 RI amp C2 ARE IN TRANSMIT CIRCUIT RQ gt 10K RIO gt 100K C7 gt 400pF C8 gt 700pF Figure 12 2 This infrared receiver identifies the transmissions intended for it and makes the received data available at D6 D9 The Microcontroller Idea Book 201 Chapter 12 accomplished you can replace the manual switches with computer control of the transmitter receiver or both The circuit uses some specialized components that do a lot of the work of detecting filtering encoding decoding and error checking of the transmissions Two of these are Motorola s MC145026 and MC145027 encoder decoder pair which are low cost chips intended for remote control applications Transmitter Circuits Figure 12 1 is the infrared transmitter which has three main functions It converts four bits of parallel data into a serial stream It then modulates the resulting signal by chopping it at 40 kilohertz And it causes one or more infrared emitting diodes to transmit the encoded modulated data to a receiver that is tuned to respond to 40 kilohertz signals The encoder chip The encoder U1 has five address inputs A1 A5 and four data inputs D6 D9 The logic states of these inputs determine the transmitted address and data The encoder outputs a different code for each of three states that the inputs may have Logic 0 1 5V or less
123. TAB USING PRINT CR Same as PRINT but outputs to LPT pin 8 BAUD and XTAL values affect the PRINT rate PRINT CR Same as PRINT but outputs to a user defined output driver Requires an assem bly language output routine at 403Ch in external program memory Setting bit 7 of internal data memory location 24h enables the output routine PROG Stores the current RAM program in the EPROM space The Microcontroller Idea Book 81 Chapter 5 PROG1 C Saves the serial port baud rate On power up or reset BASIC 52 boots without having to receive a space character The terminal s baud rate must match the stored value PROG2 C Like PROG1 but on power up or reset BASIC 52 also begins executing the first program in the EPROM space PROG3 C Like PROG1 but also saves MTOP On power up or reset BASIC 52 clears memory only to MTOP PROG4 C Like PROG2 but also saves MTOP On power up or reset BASIC 52 clears memory only to MTOP PROG5 C Like PROG3 but also reads 5Fh in external data memory on power up or reset If 5Fh contains OA5h BASIC 52 doesn t clear external data memory If data memory location 5Eh contains 34h BASIC 52 will automatically begin execut ing a program in external data memory PROG6 C Like PROG5 but if external data memory location contains 5Fh BASIC 52 calls a user written assembly language reset routine beginning at program memory 4039h PUSH expression expression C R Places the val
124. USING FN PRINT option Causes BASIC 52 to output numbers in exponential format with N significant digits BASIC 52 always outputs at least 3 significant digits Maxi mum expression is 8 Example PRINT USING F3 3 4 1 100 3 00 E O 4 10 E 0 1 00 E 2 USING 0 PRINT option Causes BASIC 52 to output numbers from 99999999 to 0 1 as decimal fractions Numbers outside this range display in USING FN format USING 0 is the default format USING 4 4 J 4 PRINT option Causes BASIC 52 to output numbers using decimal fractions with representing the number of significant digits before and after the decimal point Up to eight characters are allowed Example PRINT USING 3 4 1 100 3 00 4 10 00 00 XBY expression C R Retrieves or assigns a value in external data memory XFER C Copies the current program from the EPROM space beginning at 8010h for pro gram 1 to RAM beginning at 200h and selects RAM mode expression XOR expression C R Logical exclusive OR XTAL CR Assigns a value equal to the system s crystal frequency for use by BASIC 52 in timing calculations 86 The Microcontroller Idea Book Inputs and Outputs 6 Inputs and Outputs So far our BASIC 52 circuit consists of the 8052 BASIC microcontroller RAM nonvola tile memory for permanent program storage and a serial interface to a host computer Now it s time to add inputs and output interfaces that enable the system
125. UT B 3V LOGIC A gt 7 4HCTO3 OPEN DRAIN OUTPUT 5V TO 15V 5V l ii ANY A PUT C 15V LOGIC ee L L 74HC4050 5V 10K ANY A D TOGGLE OR n H OPEN SLIDE SWITCH L CLOSED 5V O 1 K ANYA ieee 10K INPUT 12V ON c E OPTOISOLATED ESS Zya 2 4N35 4 Figure 6 3 Input interfaces for the 74LS244 buffer 94 The Microcontroller Idea Book A 5V TTL LOGIC B 5V CMOS LOGIC C 3V LOGIC D 15V LOGIC E HIGH CURRENT CE LED G OPTOISOLATED 74LS374 Inputs and Outputs ANY TTL 5V ANY Q OR HCTMOS OUT PUT INPUT a 5V E 10K y ANY Q ANY CMOS OUTPUT INPUT aT 2 TO 5V ANY Q ANY HCMO OUT PUT INPUT 74404050 L A 5 TO 15V 5V ANY ANY Q P 10K 4000 SERIES OUT PUT CMOS INPUT 74L 26 T Wale OPEN COLLECTOR OUTPUT 5 TO 30V Se LOAD ANY Q OUT PUT 75452 UP TO PERIPHERAL 3QQmA DRIVER gt ANY Q 2200 OUTPUT x ee L ON i H OFF Tiana 5V LOAD 1 j6 l5 PRR w ANY Q 2 4 OUTPUT 330 ae L ON H OFF Figure 6 4 Output interfaces to the 73LS374 octal latch The Microcontroller Idea Book 95 Chapter 6 Output Examples Figure 6 4 shows some basic outputs that you can connect to U14 A Outputs can directly drive any TTL or HCTMOS logic input powered at 5 volts B To interface to 5 volt HCMOS or 4000 series CMOS devices
126. V 560K FEED LM385 en BOTTOM VIEW GND R3 E 330K CHOOSE R2 AND R3 FOR DESIRED VREF D R3 VREF 1 24 ADJUSTABLE VOLTAGE REFERENCI R2 Figure 9 7 The LM385 series of voltage references includes 1 2V 2 5V and an adjustable version Listing 9 3 assumes that an LM34 connects to CH2 on the ADC0848 and that VREF is 2 5V On request it displays the current temperature For a smaller range create a 1 2V reference with an LM385 1 2 and change line 70 in the program to match Another option is the LM385 adjustable reference which contains a reference diode and feedback amplifier With the addition of a voltage source and resistors in a voltage divider you can set the LM385 s output to the reference voltage you need Use the formula shown to vary the resistors for different outputs Solar Energy Figure 9 8 shows another sensor application a solar cell that generates a current proportional to the intensity of the light hitting the cell The output of the solar cell in the example varies The Microcontroller Idea Book 165 Chapter 9 SOLAR CELL OUTPUT S0mA IN FULL SUN VOUT VARIES WITH LIGHT INTENSITY LIGHT LEVEI VOUT DARK FULL SUN 4 75V Figure 9 8 vout varies with the light intensity and output current of the solar cell from 0 in darkness to 300 milliamperes in full sun The voltage across the cell is about 0 5 volt An LF353 dual op amp converts the solar cell s current into a voltage that
127. VO Port A bit 0 5 RD l Read 6 cs l Chip select 7 GND l Signal ground 8 A1 l Port select 1 9 AO l Port select 0 10 PC7 V O Port C bit 7 OBFA O Port A output buffer full 11 PC6 1 0 Port C bit 6 ACKA l Port A acknowledge 12 PC5 1 0 Port C bit 5 IBFA O Port A input buffer full 13 PC4 VO Port C bit 4 STBA l Port A strobe 14 PCO V O Port C bit O INTRB O Port B interrupt request 15 PC1 VO Port C bit 1 IBFB O Port B input buffer full OBFB O Port B output buffer full 16 PC2 VO Port C bit 2 STBB l Port B strobe ACKB l Port B acknowledge 17 PC3 1 0 Port C bit 3 INTRA O Port A interrupt request 18 PBO VO Port B bit O 19 PB1 VO Port B bit 1 20 PB2 V O Port B bit 2 100 The Microcontroller Idea Book Inputs and Outputs Pin Symbol Input Function Output 21 PB3 V O Port B bit 3 22 PB4 VO Port B bit 4 23 PB5 V O Port B bit 5 24 PB6 VO Port B bit 6 25 PB7 VO Port B bit 7 26 Vcc l Power supply 5V 27 D7 1 0 Data bit 7 28 D6 1 0 Data bit 6 29 D5 1 0 Data bit 5 30 D4 1 0 Data bit 4 31 D3 1 0 Data bit 3 32 D2 VO Data bit 2 33 D1 VO Data bit 1 34 DO 1 0 Data bit 0 35 RESET l Reset ports to input clear control register 36 WR l Write 37 PA7 V O Port A bit 7 38 PA6 V O Port A bit 6 39 PA5 V O Port A bit 5 40 PA4 1 0 Por A bit 4 The Microcontroller Idea Book 101 Chapter 6 RESE T 35 WRIT READ 56 LOW ADDRESS BUS AQ A7 DATA BUS DO D7 FCQQH RESET Cla
128. You download this file from web site http www pcports ru The Microcontroller Idea Book Circuits Programs amp Applications featuring the 8052 BASIC Microcontroller Jan Axelson Lakeview Research Madison WI copyright 1994 1997 by Jan Axelson Published by Lakeview Research 14 13 12 11 1098 765 4 Lakeview Research 5310 Chinook Ln Madison WI 53704 USA Phone 608 241 5824 Fax 608 241 5848 Email jaxelson lvr com WWW http www lvr com No part of this book except the programs and program listings may be reproduced in any form or stored in a database or retrieval system or transmitted or distributed in any form by any means electronic mechanical photocopying recording or otherwise without the prior written permission of Lakeview Research or the author except as permitted by the Copyright Act of 1976 The programs and program listings or any portion of these may be stored and executed in a computer system and may be incorporated into computer programs developed by the reader Trademarks Macintosh is a registered trademark of Apple Computer Procomm Plus and Datastorm are registered trademarks of Datastorm Technologies Inc VT100 is a registered trademark of Digital Equipment Corporation IBM is a registered trademark of International Business Machines Corporation MCS BASIC 52 and Intel are registered trademarks of Intel Corpo ration Microsoft MS DOS GW BASIC and Microsoft Windows are registered tradem
129. a complete cycle consisting of 1 high and 1 low pulse With a high duty cycle power is applied to the motor for a large proportion of the total time For slower speeds do the reverse select small values for the high pulses and large values for the low ones for a low duty cycle The actual pulse width equals the value in the PWM statement multiplied by 12 divided by the frequency of the 8052 BASIC s timing crystal So with a 12 Megahertz crystal if H 1000 and L 10 000 high pulses will be 1000 microseconds or 1 millisecond wide and U2 5V Ul 4066B 555 82C55 QUAD SWITCH TIMER 4 13 RI PAQ H ee EYOF DI SCH R2 PAI E u n E a our 3 EMABLEA PAZ 6 R3 1N914 100K 8 rt 9 10K 6 THRESH T E R4 L2lTRiG CTRL 4 wee 10 47K GE C2 RST V GND L2 0l uF V GND AA 4 18 ah 14 p clp l Se l L R5 IOUR 5V 5V 1M pcg 11 STOP START 1 DIRECTION PC7 U4 12V UDN2993B 5V al LOAD SUPPLY LOGIC re 2 ENABLE A ENABLE BH SFT SI PHASE A PHASE BLS GND GND 5 gt GND cnND HZ H ells HL fae a ENABCEA E DC 6l OUT 1A out 1BHH DC E eo HOUT 2A out 28 2 Hore TL 7 R6 C1 VEA VEB TH 7 RH C1 DUAL H BRIDGE MOTOR DRIVERS RH PARALLEL COMBINATION OPTIONAL OF RI R5 AS DETERMINED SECOND BY U2 S SWITCH SETTINGS MOTOR Figure 11 6 A 4066B quad switch and 555 timer enable you
130. a bit 3 37 P0 2 1 0 Port O bit 2 AD2 Address data bit 2 38 PO 1 W O Port O bit 1 AD1 Address data bit 1 39 P0 0 VO Port O bit O ADO Address data bit 0 40 Vcc Input Supply voltage The Microcontroller Idea Book 19 Chapter 2 RAM RAM random access memory is where programs store information for temporary use Unlike ROM the CPU can write to RAM as well as read it Any information stored in RAM is lost when power is removed from the chip The 8052 has 256 bytes of RAM BASIC 52 uses much of this for its own operations with a few bytes available to users 1 O Ports I O Input Output Ports enable the 8052 to read and write to external memory and other components The 8052 has four 8 bit I O ports Ports 0 3 As the name suggests the ports can act as inputs to be read or outputs to be written to Many of the port bits have optional alternate functions relating to accessing external memory using the on chip timer counters detecting external interrupts and handling serial communications BASIC 52 assigns alternate functions to the remaining port bits Some of these functions are required by BASIC 52 while others are optional If you don t use an alternate function you can use the bit for any control monitoring or other purpose in your application Accessing external memory The largest alternate use of the ports has to do with accessing external memory Although the 8052 is a single chip computer a complete 8052 BASIC s
131. a computer at all In general a computer is the way to go when the circuits must make complex decisions or deal with complex data For example a simple AND gate can easily decide whether or not two inputs are both valid logic highs and will change its output accordingly But it would require many small scale chips to build a circuit that stores a series of values representing sensor outputs and the times they occurred and displays the information in an easily understandable form This type of application is where microcontrollers come in handy Inside microcontrollers are little more than a carefully designed array of logic gates and memory cells but modern fabrication processes allow thousands of these to fit on a single chip Since the basic functions of a microcontroller performing arithmetic logic data moving and program branching functions are common ones that are useful in many applications it s practical to design and market a chip that performs these functions The user accesses the abilities of the microcontroller by writing a program that performs the desired functions On the other end of the scale how do you know if an idea is suitable for a microcontroller or whether you should use a full desktop computer If your design requires users to enter or view complex commands data or graphical information or if you need large amounts of data or program storage then a system with keyboard full screen display and disk drives
132. ake a big difference in how long it takes to get a system up and running As with programming you have several options here as well Testing in EPROM One way is to burn your program into EPROM install the EPROM in your system run the program and observe the results If problems occur as they usually will you modify the program erase and reburn the EPROM and try again repeating as many times as necessary until the system is operating properly Development systems Another option is to use a development system A typical develop ment system consists of a monitor program which is a program stored in EPROM or other memory in the microcontroller system and a serial link to a personal computer Using the The Microcontroller Idea Book 9 Chapter 1 abilities of the monitor program you can load your program from a personal computer into RAM instead of the more permanent EPROM on the microcontroller system then run the program modify it and retry as often as necessary until the program is working properly Most development systems also allow single stepping setting breakpoints and viewing and changing the data in memory In single stepping you run the program one step at time pausing after each step so you can more easily monitor what the circuits and program are doing at each step A breakpoint is a program location where the program stops executing and waits for a command to continue You can set breakpoints at critical spots in
133. al port out TXD Serial transmit 12 P3 2 VO Port 3 bit 2 DMA DMA request INTO External interrupt 0 REQ 13 P3 3 VO Port 3 bit 3 INT1 External interrupt 1 14 P3 4 VO Port 3 bit 4 TO Timer 0 external input 15 P3 5 VO Port 3 bit 5 T1 Timer 1 external input 16 P3 6 VO Port 3 bit 6 WR Write strobe for external memory 17 P37 VO Port 3 bit 7 RD Read strobe for external memory 18 XTAL1 Input Inverting oscillator amplifier crystal 19 XTAL2 Output Inverting oscillator amplifier crystal 20 VSS Input Circuit ground Tne Microcontroller Idea Book Table 2 2 page 2 of 2 Inside the 8052 BASIC Pin Symbol Input 8052 8052 BASIC Additions Output Function none on pins 21 40 21 P2 0 VO Port 2 bit 0 A8 Address bit 8 22 P2 1 VO Port 2 bit 1 AQ Address bit 9 23 P2 2 1 0 Port 2 bit 2 A10 Address bit 10 24 P2 3 1 0 Port 2 bit 3 A11 Address bit 11 25 P2 4 VO Port 2 bit 4 A12 Address bit 12 26 P2 5 1 0 Port 2 bit 5 A13 Address bit 13 27 P2 6 1 0 Port 2 bit 6 A14 Address bit 14 28 P2 7 VO Port 2 bit 7 A15 Address bit 15 29 PSEN Output Program store enable Read strobe for external program memory 30 ALE Output Address latch enable 31 EA Input External access enable for program memory 32 PO 7 1 0 Port O bit 7 AD7 Address data bit 7 33 P0 6 1 0 Port 0 bit 6 AD6 Address data bit 6 34 P0 5 1 0 Port 0 bit 5 AD5 Address data bit 5 35 P0 4 1 0 Port O bit 4 AD4 Address data bit 4 36 P0 3 VO Port 0 bit 3 AD3 Address dat
134. also available Telephone The Microcontroller Idea Book 117 Chapter 7 E a o o Ais 4 es ace z Y AN Sil ie D eral EE Eg fy Y2 7 ST 9 E ae ena me ill n as in Ul rea v3 ye is a X X2 XS X4 Figure 7 7 A matrix encoded keypad style keypads are widely available and versatile since they have all 10 digits plus two keys and that you can designate for special functions Decoding Unfamiliar Keypads You can find surplus keypads for a dollar or so each These usually include no explanation of their pin connections so it s up to you to figure out how to decode them To decode an unknown keypad you need only an ohmmeter and a pencil and paper to record your findings To determine the key connections one by one begin by clipping an ohmmeter lead to one of the keypad s connector pins Set the ohmmeter to a low scale such as 200 ohms Press a key and hold it down while touching the other ohmmeter lead to each of the remaining keypad pins in turn When the ohmmeter reads a few ohms or less you ve found the pins that correspond to the key in question If you find no connection move the first ohmmeter lead to a different pin and repeat the procedure When you find the two pins that connect write down their numbers and the key they correspond to Follow
135. amperes is suitable for the transmitter or receiver Chances are that you Il want to operate the transmitter receiver or both from batteries Four NiCad cells in series create a reasonably stable source at around 4 8V Using unregulated alkaline cells is less desirable since their voltage drops quite a bit as they discharge from 1 5V to around 1V per cell and there is no series combination of 1 5V cells that meets MOD1 s supply voltage recommendation A regulated supply is another option When the supply voltage varies U3 s output frequency and MOD1 s frequency response also vary slightly A regulated supply eliminates these concerns Figure 12 5 shows a 5V supply that uses five or six NiCad or alkaline cells and National Semiconductor s 2931T 5 0 low drop out 5V regulator The regulator requires an input of just 5 6V for a 5V output at 100 milliamperes You can also use a 9V alkaline NiCad battery to power the regulator but due to the low capacities of this type you ll get fewer hours of use LM2931T 5 0 IN OUT p gt 5V OUT OUT FT O GND GND Tioout IN 5 6 TO 9V r LM2931T 5 0 5V REGULATOR Figure 12 5 The LM2931T 5 0 voltage regulator creates a stable 5V supply with an input of 5 6V or greater The Microcontroller Idea Book 207 Chapter 12 Basic tests When you have the circuits built and tested if you have an oscilloscope or frequency counter you can meas
136. ample the label DO tells you to interconnect these points pin 39 of U2 pin 3 of U4 pin 11 of U7 and one end of R2 Other connections are indicated by labels For example the WRITE label tells you to connect pin 16 of U2 and pin 27 of U7 Another point to be aware of is the conventions used in the schematics and text of this book for indicating an active low signal or a signal that is valid or enabled when low In this book the schematics use a leading hyphen WRITE while the text uses an overscore WRITE Their meanings are the same The Microcontroller Idea Book 31 Chapter 3 DOT INDICATES PIN 100 wee 14 2 13 3 12 PINS COUNT UP 4 11 COUNTER 5 10 CLOCKWISE FROM PIN 1 6 9 8 Leonie OP VIE PINS POINTING DOWN 7 78 INTEGRATED CIRCUIT DUAL IN LINE PACKAGE DIP ANODE CATHODE POSITIVE NEGATIVE Se TERMINALS LAT EDG INDICATES moa ANODE LEAD IS gt E AN OFTEN LONGER STRIPE INDICATES SIDE BOTTOM CATHODE END VIEW VIEW DIODE LE NEGATIV TERMINAL LABELED 5 POSITIVE JN TERMINAL AXIAL LEAD RREEPER ALUMINUM z RADIAL LEAD a N TANTALUM AN POSITIVE LEAD IS OFTEN LONGER
137. and outputs provided by U12 and U14 there are specialized peripheral interface chips that you can add to your system Table 6 1 lists several examples One of the most popular of these is the 8255 programmable peripheral interface or PPI Figure 6 5 shows the pinout and Table 6 2 shows the pin functions The chip adds 24 bits of I O plus the option to use special control and handshaking signals to communicate with peripherals Intel originally introduced the 8255 as a peripheral for its 8085 microprocessor but it remains a popular chip for use with 8052s and other computer chips Manufacturers of compatible chips include AMD OKI Toshiba and NEC which calls its chip the uPD71055 If you use the 8255 you ll want a copy of its data sheet which more fully explains its abilities and configuration options 8255 Variants You have a choice of the original NMOS 8255 or the CMOS 82C55 The CMOS version usually costs a little more but has some advantages First it has lower power consumption with supply currents of 10 milliamperes 10 microamperes in standby mode with CS high compared to 120 milliamperes for the 8255 98 Tne Microcontroller Idea Book Inputs and Outputs The 82C55 also has CMOS compatible outputs which means that they can drive either LSTTL or CMOS inputs When driving CMOS inputs the NMOS 8255 s outputs should have pull up resistors to ensure that high outputs are at least 3 5 volts A third advantage to the 8
138. anguage Routines into memory in the 8052 BASIC system The following sections describe each of these in more detail Programming Reference This book concentrates on BASIC 52 programming I ve included enough information about assembly language to get you started programming plus what you need to know to interface assembly language routines to BASIC 52 But there is much more to assembly language programming than I can cover here If you are an experienced assembly language programmer Intel s Embedded Microcontrol lers handbook or a similar reference from another 8052 vendor may be all you need as a reference The handbook includes a programmer s guide and describes each of the 8052 s instructions If you re just starting out with assembly language you might want to invest in a more complete text that includes examples and explanations of how to put together a program Examples can be extremely useful for seeing how to do common tasks like generating a timing delay or handling an interrupt Appendix A lists several books on the 8051 family that include programming examples and tutorials Text Editor The text editor is the software that you use to create your source files The editor program must be able to create files in straight ASCII format without adding any formatting codes Just about all word processors have this ability as do simpler text editors like MS DOS s EDIT Assembler The assembler is the program th
139. ant Connect VOUT to any input port pins Measuring Analog Signals Sometimes you need something more sophisticated than a simple level detector An analog to digital converter ADC enables you to measure the precise value of an analog voltage Some versions of the 8052 microcontroller including Philips 80C562 include an on chip ADC but the 8052 BASIC doesn t have this feature so you have to add it externally There are dozens of converters available with varying resolution accuracy speed method of conversion number of analog inputs and so on Another option is to use an integrated sensor that contains its own ADC and has a digital output National Semiconductor s ADC0848 is an easy to use low cost general purpose eight channel ADC In many ways the ADC0848 is similar to National s long popular ADC0808 9 A D converters but with some advantages The ADC0848 does not require an external clock its control signals interface directly to many microcontrollers and it is faster with a typical conversion time of 30 microseconds National s data sheet for the ADC0848 has complete specifications applications informa tion and example circuits You ll want a copy of the data sheet if you plan to use the chip 158 The Microcontroller Idea Book Using Sensors to Detect and Measure ADC 848 5V A D CONVERTER 24 11 VREF cH 12 cH E READ HRD Cs Weare
140. ard for the added component The Microcontroller Idea Book 239 Chapter 14 For experienced assembly language programmers another reason for placing BASIC 52 in external memory is so that you can modify the source file for BASIC 52 You then can reassemble your modified source file and use the new version in your projects In this way you can add functions or make other changes to BASIC 52 itself To do this you must have a copy of BASIC 52 s source code which has been available on Intel s and Philips BBS s plus Intel s ASM51 or a compatible 805 1 family assembler Iota Systems is one vendor that has customized BASIC 52 in this way with an expanded BASIC 52 PLUS that runs from external EPROM on Iota s 8052 BASIC boards BASIC 52 PLUS includes commands for uploading and downloading Intel Hex files as well as other enhancements and bug fixes Copying BASIC 52 To copy BASIC 52 from ROM to NVRAM you can use the same circuits shown in Figures 3 1 and 4 3 Use a DS1225 8K NV RAM at U8 Listing 14 1 is a program that copies the 8052 BASIC s ROM from 0 to 1FFFh in internal code memory to U8 at 8000 9FFFh in external data or code data memory Boot up your system enter or upload Listing 14 1 and run it Then power down and remove the NV RAM at U8 which now contains a copy of BASIC 52 If you prefer you can use a 28 C 64 8K EEPROM instead of NV RAM at U8 Because the write cycle time of EEPROMs is often 2 to 10 milliseconds you
141. arks of Microsoft Corporation Philips is a registered trademark of Philips International BV The author and publisher have used their best efforts in preparing this book and the materials in it The author built and tested the electronic circuits described ran and tested the computer programs presented and reviewed all materials for completeness and accuracy The author and publisher make no warranty with regard to the circuit schematics program listings and other materials in this book The author and publisher take no responsibility for any damages resulting from any use of the material in this book ISBN 0 9650819 4 X designs and patents acts this publication may only be reproduced stored or transmitted in any form or by any means with the prior Apart from any fair dealing for the purposes of research or private study or criticism or review as permitted under the relevant copyright permission in writing of the publisher eBooks Corporation Chapter 1 Chapter 2 Chapter 3 Chapter 4 Table of Contents Microcontroller Basics What s a Microcontroller 1 A Little History 2 New Tools 3 Project Steps 4 Inside the 8052 BASIC Possibilities 11 Limits 13 What You Need 14 The 8051 Family 16 Elements of the 8052 and 8052 BASIC 17 Powering Up About the Circuit 23 Circuit Construction 30 Powering Up 35 Basic Tests 38 Simple Programs to Try 40 Exiting Programs 44 Saving Programs Nonvolatile Memory Optio
142. art and wire the desired bit to the relay s input with the relay s input connected to GND Look for a relay with a control voltage of 5 volts or less and input control current of 15 milliamperes or less The relay s rated output voltages and currents should be greater than those of the load you intend to switch Take care to work safely when you re wiring testing and using circuits that control high current or high voltage loads For circuits that connect to 117V line voltage and have a metal chassis you can ground the chassis by connecting it to the safety ground wire in a 3 wire power cord Insulate any exposed wires and terminals with heat shrinkable tubing If in doubt about how to wire the power connections get qualified help before you continue You can control a relay from any output port bit Just write a 1 or 0 to the corresponding bit to switch the load on or off If you control a solid state relay with a port bit on an 8255 or the 8052 BASIC you may have to add an LSTTL or HCMOS buffer such as a 74LS244 to supply enough current to the relay s control inputs Controlling a Switch Matrix Figure 11 2 shows how you can use 9 output bits to control an 8 x 8 array of electronic switches You can connect any of eight X inputs to any of eight Y inputs in any combination Possible applications include switching audio or video signals to different monitors or recording instruments selecting inputs for test equipment or a
143. asier in the long run to test the pieces first and BASIC 52 makes this easy to do Command and Run Modes BASIC 52 has two modes of operation command and run Command mode refers to anything you type without a line number BASIC 52 executes these lines immediately after you press ENTER Run mode refers to running stored programs with the RUN command A program consists of a series of program lines with each line beginning with a line number BASIC 52 includes some keywords that you can use only in command mode but not in programs PROG is an example Most of BASIC 52 s other keywords are usable in either command or run mode A few such as DO WHILE are usable in RUN mode only Tips for Writing BASIC 52 Programs The following advice is intended to make your programs easier to write and debug and to help you avoid some common mistakes e Number program lines by 10s Each line in a BASIC 52 program must begin with a line number BASIC 52 uses the numbers to order the statements Traditionally BASIC programs begin at line 10 and count up in multiples of 10 20 30 and so on This way if you later discover that you need to add a few lines in the middle you can using the unused numbers that remain e Divide long programs into modules Break up big projects Use subroutines for independent functions A subroutine is a block of statements that the main program jumps to with a GOSUB statement At the end of the subroutine a RETURN s
144. at creates an object or executable file from your source file If you write assembly language programs for your personal computer you use an as sembler such as MASM for 80x86 microprocessors MASM creates files that will exe cute on 80x86 systems using the 80x86 s instruction set To assemble a program for an 8052 microcontroller you need a special type of assembler called a cross assembler The cross assembler runs on your personal or host computer but creates programs to run on a different chip such as the 8052 Assemblers for 805 1 family chips which you can use for 8052 programming are widely available Appendix A lists vendors of assemblers and BBS s from which you can download free and shareware assemblers The Microcontroller Idea Book 219 Chapter 13 Most 8051 family cross assemblers create files in Intel Hex format which is convenient for EPROM programming and uploading to RAM During the assembly process if the assem bler encounters a program line that is incomplete or not understandable it will display an error message describing the problem The assembler will also create a listing file that shows each line of your source file alongside the addresses and machine codes of the object file and any error messages generated Memory for Program Storage On your BASIC 52 system you ll need room in external memory for storing your assem bly language routines Remember that the 8052 has separate control signals for ac
145. ate AND gate U3C and wire WRITE U2 pin 16 directly to WE U8 pin 27 If you make these changes bits 4 and 5 of Port 1 are free for any use you want And since NVRAM requires no programming voltage bit 3 of Port 1 is also free for other uses If you don t make the changes you can still run BASIC 52 from external memory but if you try to use PROG FPROG or PGM the system will crash You can also make these changes in a circuit that uses an 8052 BASIC to free up some port pins if you use the program described below instead of the programming commands U2 can be any 80 C 32 or 80 C 52 U7 can be an 8K or 32K static RAM addressed beginning at 0 in data memory Figure 14 1 shows the wiring for NVRAM EPROM or EEPROM that contains BASIC 52 This chip is accessed from 0 to 1 FFFh in external code memory U8 is NVRAM accessed from 8000h to 9FFFh in combined code data memory for storing BASIC 52 programs and assembly language routines Storing BASIC 52 Programs With BASIC 52 in external memory you can t use the built in programming functions but there is another way to store programs Using the circuits described above write and test your BASIC 52 programs as usual When you want to store a program permanently append the code in Listing 14 2 to your program The code is shown beginning at line 9000 but it can begin at any line number after the END statement in the program you want to save To store a program in U8 type GOTO
146. ater currents The amount of allowable current depends on the pulse s duty cycle which equals the width of a pulse divided by the width of a complete on and off cycle Unfortunately the data sheets often do not say how to determine the limits for a particular pulse width and repetition rate Occasionally you get a graph of maximum forward current versus pulse width and duty cycle Other data sheets just offer a few examples The F5D1 s data sheet includes just two ratings for pulsed operation For 10 microsecond pulses repeating at 100 Hz the IRED s maximum peak current is 3 amperes or 30 times the continuous rating And for even shorter 1 microsecond pulses repeating at 200 Hz the maximum is 10 amperes But neither of these describes the situation for the infrared transmitter 214 The Microcontroller Idea Book Wireless Links In the infrared link the amount of time the IRED is on depends on what information it is sending and how often it transmits When the IRED is pulsed at 40 kilohertz it is on for just half of each 25 microsecond cycle But the IRED pulses only when transmitting logic high outputs from the encoder For logic low outputs and when no data is transmitting the IRED is off With the encoder chip clocked at 1 kilohertz an encoded 1 contains two 3 5 millisecond high pulses and two 0 5 millisecond low pulses This means that the IRED is pulsing almost 90 percent of the total time If the 40 kilohertz oscillator
147. auses the the converted value to appear at DBO DB7 where the 8052 BASIC reads it The INTR pin indicates when a conversion is complete and can be used to trigger a read operation INTR is low when a conversion has occurred that has not yet been read It goes high after a read and remains high until the next conversion is completed BASIC 52 is slow enough that you don t have to worry about waiting the maximum 60 microseconds between requesting a conversion and reading the result so you can ignore INTR and read the result any time after a write Packaging Options The ADC0848 comes in a 24 pin skinny DIP with the pin rows spaced 0 3 apart as on a 14 pin DIP Sockets of this size especially wire wrap can be hard to find but in a pinch you can place a 16 pin and 8 pin socket end to end If you need only four analog inputs use the ADC0844 in a 20 pin skinny DIP Sensor Examples Now let s look a couple of examples of sensors that you can connect to the ADC0848 Temperature The first is an LM34 temperature sensor Unlike many other temperature sensors the LM34 requires no calibration Its output is a simple 10 millivolts per degree Fahrenheit As Figure 9 6 shows it s available in several versions The ones with a narrower range or lower resolution are cheaper If you prefer Celsius readings use the LM35 Figure 9 7 shows how to use an LM385 2 5 voltage reference to set the ADC s VREF to 2 5V The converter then can measu
148. by byte This is acceptable for short programs but quickly becomes tedious with a program of any length Computer control simplifies the job greatly With an EPROM programmer that connects to a personal computer you can write a program at your keyboard save it to disk if you wish and store the program in EPROM in a few easy steps Data sheets for EPROMs rarely specify the number of erase and reprogramming cycles a device is guaranteed for but a typical EPROM should endure 100 erase program cycles and usually many more EEPROMs are much like EPROMs except that they are electrically erasable no ultraviolet source is required Limitations of EEPROMs include slow speed high cost and a limited number of times that they can be reprogrammed typically 10 000 to 100 000 ROMs are cost effective when you need thousands of copies of a single program ROMs must be factory programmed and once programmed can t be changed NVRAM typically includes a lithium cell control circuits and RAM encapsulated in a single IC package When power is removed from the circuit the lithium cell takes over and preserves the information in RAM for 10 years or more You can reprogram an NVRAM n infinite number of times with the only limitation being battery life Flash EPROM is electrically erasable like EEPROM but most Flash devices erase all at once or in a few large blocks rather than byte by byte like EEPROM Some Flash EPROMs require special programming vo
149. cessing code and data memory For uploading into RAM and testing you must use combined code data memory since you need data memory s WR signal to write the routine into memory and code memory s PSEN to enable the 8052 to execute the routine You can upload routines into any unused combined code data memory from 2000h to FFFFh Code memory from 0 to 1FFFh is not available because the 8052 BASIC chip uses these locations for the BASIC 52 interpreter If you have a 32K RAM addressed at 0 in combined code data memory you can use the area above 1 FFFh for storing and testing assembly lan guage routines For combined data code memory in Figure 3 1 s circuit move the connec tion at pin 22 of U7 from pin 17 of U2 READ to pin 3 of U3A RDANY With this setup however if you upload your programs into ordinary RAM you ll lose them when you power down For more permanent storage there are several options You can use a 32K NV RAM such as Dallas Semiconductor s DS1235 or a Dallas 1213C SmartSocket and 62256 SRAM in place of ordinary RAM at 0 Although you don t need battery backup for data memory from 0 to 1FFFh it does no harm Again you must connect RDANY not READ to pin 22 of the NVRAM To prevent overwriting your assembly language routines in RAM when you reboot set MTOP to 1FFFh or another value that is lower than the beginning of your routines and execute BASIC 52 s PROG3 command as described in Chapter 3 You must
150. combined code data memory For EEPROM or NVRAM wire the socket exactly like U8 in Figure 4 3 except wire pin 1 of U9 to chip select AOOOh pin 10 of U6 in Figure 3 1 instead of to 8000h For EPROM programming also connect Figure 4 5 s circuits to pins 1 and 28 of the EPROM for the programming voltages The Microcontroller Idea Book 237 Chapter 13 With these added components and Listing B 2 you can program a DS1225 NV RAM a 28 C 64 EEPROM or a 27 C 64 EPROM with an Intel Hex file One use would be to program an EPROM for a non BASIC 52 system where EA is tied low and on bootup the 8052 runs a program beginning at 0 in external code memory instead of running the BASIC 52 interpreter in internal ROM For this use you must add AOOOh to the values given in all ORG directives For example you would change ORG 0 to ORG A000h and change ORG 200h to ORG A200h You can then use Listing B 2 to copy the program into the EPROM at A000h remove the EPROM and install it at 0 in code memory in your non BASIC 52 system On bootup the 8052 will run the program in EPROM Another Way to Program EPROMs Listing 13 8 is another program that you can use to copy information from external data memory into an EPROM EEPROM or NVRAM To use this program you must specify the locations to copy the source the locations to copy to the destination and the device type to copy to The program does the rest With this program you can copy information dir
151. come this limitation For example with mirrors you can transmit around corners Radio Links Another possibility for wireless links is to use radio frequencies Radio transmissions consist of high frequency electromagnetic waves that travel through the atmosphere Most radio waves will also pass through windows walls and other solid objects This makes radio useful where a direct line of sight between transmitter and receiver isn t available Radio can also be a good choice for outdoor links where daylight may interfere with infrared transmissions and wired links are inconvenient Radio circuits require special construction techniques and radio transmissions must not violate regulations of agencies such as the Federal Communications Commission FCC For these reasons the easiest option is to buy the transmitters and receivers for your link rather than build them yourself One source of low cost radio frequency transmitter and receiver circuits is Electronics 123 The links transmit in the range 300 315 Megahertz a frequency band used by many garage door openers and alarm systems The boards come with complete schematics and instructions for use The circuits are similar to the infrared transmitting circuits described earlier The transmitter sends 4 bit codes to a receiver identified by an 8 bit address The transmitter and receiver use Holtek s HT 12E encoder and HT 12D or HT 12F decoder chips also available sepa rately from Elect
152. crocontroller Idea Book 161 Chapter 9 S INGLE ENDED HIE SENSOR h A RA EEE SENSOR 2 H4 eri SENSOR 3 H4 cHae SENSOR 4 H4 chs f SENSOR 5 j4 cH6 SENSOR 6 4 dye SENSOR 7 H4 cha SENSOR 8 H4 AGND 2 lt 7 DIFFERENTIAL cH I SENSOR h ADCO848 3 cH3 SENSOR 2 j cH4 cH5 SENSOR 3 j cHe cr7 SENSOR 4 j cha PSEUDO DIFFERENTIAL cH I SENSOR h PORREN E SENSOR 2 H4 chs l SENSOR 3 H4 cHae SENSOR 4 j4 cH5 f SENSOR 5 H4 cHe SENSOR 6 4 cr7 SENSOR 7 H4 cha Figure 9 5 Measurement modes available with the ADC0848 are single ended A differential B and pseudodifferential C 162 The Microcontroller Idea Book Using Sensors to Detect and Measure Listing 9 2 Displays measurements of channels 1 through 8 on the ADC0848 10 REM use single ended mode 20 REM set A to address of ADC 30 A 0C000H 40 FOR I 1 TO 8 50 XBY A 84 I 1 60 PRINT Channel 1I PHO XBY A 70 NEXT I 80 END Writing to the converter causes the conversion to begin automatically When the conversion is complete a read operation to the converter s address c
153. d to build a personal computer from scratch since mass production has drastically lowered the price of assembled systems At most building a personal computer now involves only installing assembled boards and other major components in an enclosure A personal computer like Apple s Macintosh or IBM s PC is a general purpose machine since you can use it for many applications word processing spreadsheets computer aided design and more just by loading the appropriate software from disk into memory Interfaces to personal computers are for the most part standard ones like those to video displays keyboards and printers 2 The Microcontroller Idea Book Microcontroller Basics But along with cheap powerful and versatile personal computers has developed a new interest in small customized computers for specific uses Each of these small computers is dedicated to one task or a set of closely related tasks Adding computer power to a device can enable it to do more or do it faster better or more cheaply For example automobile engine controllers have helped to reduce harmful exhaust emissions And microcontrollers inside computer modems have made it easy to add features and abilities beyond the basic computer to phone line interface In addition to their use in mass produced products like these it s also become feasible to design computer power into one of a kind projects such as an environmental controller for a scientific study o
154. data The 8052 BASIC chip is available in both NMOS and CMOS versions The original 8052 BASIC was an NMOS chip offered directly from Intel Intel s term for its NMOS process is HMOS Although Intel never offered a CMOS version directly Micromint became a source by ordering a batch of CMOS 8052 s with the BASIC 52 programming language in ROM The CMOS version the 80C52 BASIC has maximum power consump tion of 30 milliamperes compared to 175 milliamperes for the NMOS 8052 BASIC All microcontrollers have a defined instruction set which consists of the binary words that cause the CPU to carry out specific operations For example the instruction 00 0 01 0 tells an 8052 to add the values in two locations The binary instructions are also known as operation codes or opcodes for short The opcodes perform basic functions like adding subtracting logic operations moving and copying data and controlling program branching Control circuits often require reading or changing single bits of input or output rather than reading and writing a byte at a time For example a microcontroller might use the eight bits of an output port to switch power to eight sockets If each socket must operate independently of the others a way is needed to change each bit without affecting the others Many microcontrollers include bit manipulation also called Boolean opcodes that easily allow programs to set clear compare copy or perform other logic operations o
155. days match Symbol Function Symbol Function EOSC Enable Oscillator PU LVL Pulse Level Triggered Interrupts ESQW Enable Square Wave Out WAM Watchdog Alarm Mask TE Transfer Enable TDM Time of day Mask IPSW Interrupt Switch WAF Watchdog Alarm Flag IBH LO Interrupt B High Low Trigger TDF Time of day Flag The Microcontroller Idea Book 177 Chapter 10 To generate an interrupt at a specific time you select an alarm frequency by setting or clearing three mask bits bit 7 of registers 3 5 and 7 and storing the desired alarm data in bits 0 6 of the same registers Clearing a register s mask bit means that the DS1286 will use values in that register to determine the alarm frequency Setting a mask bit means that the DS1286 will ignore the information in the register For example to generate an interrupt at 3 15 daily you would store the following values Register Mask Byte Alarm Data 3 0001 0101 15 minutes 5 0000 0011 3 hours 7 1XXX XXXX days X don t care Table 10 3 Decimal numbers and their equivalents in binary and binary coded decimal The values 0 9 are identical in BCD and binary Decimal Binary coded Decimal BCD Binary 0 0000 0000 0000 0000 1 0000 0001 0000 0001 2 0000 0010 0000 0010 3 0000 0011 0000 0011 4 0000 0100 0000 0100 5 0000 0101 0000 0101 6 0000 0110 0000 0110 7 0000 0111 0000 0111 8 0000 1000 0000 1000 9 0000 1001 0000 1001 10 0001 0000 0000 1010 11 0001 0001 0000 1011 19 0001 100
156. display with low power consumption look for types labeled high efficiency One disadvantage to LEDs is that the light from most is hard to detect in bright light especially outdoors A tinted transparent sheet of plastic mounted over the display can make it more visible in bright light For red LEDs transparent red or purple works well For best visibility over a wide area look for LEDs with a wide viewing angle This means that the LED emits light in a wide cone so you don t need to view it straight on LED Interfaces Figure 8 1 shows examples of LED interfaces to output ports in an 8052 BASIC system The outputs of the 80 C 52 and 82 C 55 can t provide enough current to drive an LED directly But you can drive an LED with a 74LS374 or 74HC374 latch A B or with a buffer or inverter driven by any output port C D With LSTTL drivers you should design your circuit so that a low output turns on the LED since LSTTL outputs can sink more current than they can source With HCMOS or HCTMOS outputs either a high or low output can turn on the LED Use a series resistor to limit the current through the LED For a brighter display decrease the value of the resistor Most LEDs can handle 20 milliamperes of continuous current You can measure the current directly by connecting an ammeter in series with the LED and resistor Or you can calculate the current by measuring the the voltage across the series resistor and dividing it by the re
157. don t need a separate EPROM programmer SERIAL LINK BETWEEN 8052 BASIC AND PERSONAL COMPUTER WHEN PROGRAM DEVELOPMENT IS COMPLETE SERIAL LINK MAY BE DISCONNECTED FOR STAND ALONE 8052 BASIC OPERATION i US H l DEVI CES PERSONAL COMPUTER 8 52 BASIC CIRCUIT ALLOWS YOU TO ENTER DISPLAY RUNS AND STORES PROGRAMS TEST AND EDIT PROGRAMS Figure 2 1 Setup for working with the 8052 BASIC 12 The Microcontroller Idea Book Inside the 8052 BASIC e You can also store programs on your personal computer s disk You can write or edit programs on your personal computer and then upload them to the 8052 BASIC system e To the basic circuits you can add displays switches keypads relays and other components depending on the needs of your project e After program development you can disconnect the link to the personal computer and let the 8052 BASIC system run its stored program on its own Limits No single product is ideal for every use These are some of the limitations to the 8052 BA SIC e Program execution can be slow compared with programs that run on more powerful computers or programs written in assembly language A typical program line in BASIC 52 takes several milliseconds to execute Because of this there are some tasks that BASIC 52 just can t handle for example detecting and responding to an interrupt within a few microseconds But f
158. dress and data On the other end you need to detect the transmitted signal find out if the address matches and if so convert the received data into a usable format Figure 12 2 shows a circuit that does these using an infrared receiver module and an MC145027 decoder that complements Figure 12 1 s encoder The infrared receiver module MOD1 is a Sharp GP1U52X infrared receiver module Its circuits are enclosed in a metal cube about half an inch on each side The module has just 204 The Microcontroller Idea Book Wireless Links fp A PHOTODIODE AMPLIFIER IMI TER GP1U52X A L Sow BANDPASS FILTER DEMODULATOR INTEGRATOR COMPARATOR Figure 12 4 The GP1U52X infrared receiver contains a detector amplifier and filter When the receiver detects infrared energy pulsed at 40kHz vout goes low three connections to 5V ground and VOUT You can find this part at Radio Shack and other sources Another option for MOD is Lite On s LTM 8834 2 carried by Digi Key It has a 32 7 kHz center frequency rather than 40 kilohertz so you ll have to adjust the oscillator either by adjusting R8 or by changing XTAL1 Digi Key has a 32 56 kHz crystal that s a good match for this receiver When MODI detects infrared energy that is pulsed at 40 kilohertz its VOUT is low Otherwise VOUT is high Figure 12 4 shows a block diagram of what s inside the module The photodiode emits a current when it senses infrared energy in the rang
159. dress to read 1000H 55H is stored in address 1000H If you write to an address outside the range specified as free memory you will overwrite the RAM currently in use to store your program and run BASIC 52 If you do this accidentally your system may crash and you ll have to reset the system and re enter the program If you prefer decimal numbers to hex notation change each PHO in the program to PRINT PHO includes a period PRINT does not Real time Clock Listing 3 4 demonstrates BASIC 52 s real time clock by displaying an on screen 60 second timer 42 Tne Microcontroller Idea Book Powering Up Listing 3 3 Allows user to read and write to external memory 10 DO 20 INPUT Enter 0 read 1 write or 2 quit RW 30 IF RW 0 THEN GOSUB 70 40 IF RW 1 THEN GOSUB 120 50 WHILE RW lt gt 2 60 END 70 PHO External RAM ranges from 0 to MTOP 80 INPUT Enter an address to read A 90 B XBY A 100 PHO B is stored in address A 110 RETURN 120 PHO Free memory ranges from LEN 512 to MTOP 130 INPUT Enter an address to write to A 140 INPUT Enter data to be written B 150 XBY A B 160 PHO B has been written to address A 170 RETURN For the timer to be accurate you must set XTAL to match the timing crystal your system uses Further Experiments Feel free to continue experimenting with BASIC 52 programs using the programming reference as a guide You
160. dressed at OE400h If you use a 74LS374 add 10K pullups to the outputs to ensure that logic high inputs to U3 and U5 meet the specified minimum of 3 5V You can choose from several modes of operation for the motor with each using a different sequence of pulses The frequency and sequence of the pulses determine the speed of the motor In the circuit shown after you write values to the port to set the speed and operating mode the motor continues to run automatically using the selected parameters This frees the The Microcontroller Idea Book 191 Chapter 11 5V R5 1K U3 U2 4066B DATA BUS 74HC374 QUAD SWITCH DQ D7 LATCH 2 3 RI 1D 10 2D 20 2 L a 300K 6 5 R2 3D 30 4D 402 4 ca 12 6 R3 5D 50 6D so 8 ne g 9K 7D 706 2 R4 aD 302 l L 1o 43k 2 E400H l1 ll V GND mle WRITE J ieee ya F 5 ELT Sa f Olu 74HCTO2 om z deg u5 UCN5804B STEPPER MOTOR Es TRANSLATOR DR IVER T E SE STEP TP UE RE OUN CY a eee ete 101 NO 14 DIRECTION 2 N Ate ae 0 40 0 15 PALF STEP mg D2 Ie LU l l 9 PHASE K muutu 150E KBs US MODE SELECT K 7 DRIVE PIN PIN T FORMAT 9 10 8 D4 2 PHASE i GND RAE TEASE ae 1 PHASE r ni i6 la l5 Talis INSB 18 4 PHASE Lee STE ra E d at SCHOTTKY UNIPOLAR 5V STEPPER MOTO
161. ds per cycle Adding Assembly Language To speed things up Listing 13 5 is an assembly language routine that performs the functions of lines 150 180 in Listing 13 4 As in the original program Listing 13 5 copies values in sequence from RAM to E400h repeating the sequence after 256 writes The routine illustrates a couple of major differences between BASIC and assembly language program ming One is that assembly language has no built in FOR DO or WHILE loops Instead you have to create loop structures from the instructions available Listing 13 5 creates a 256 step 228 The Microcontroller Idea Book Calling Assembly language Routines Listing 13 5 Assembly language sine wave routine for Figure 13 2 s circuit Reads and copies values in sequence from locations 3000h to 30FFh to E400h A DAC0832 generates a sine wave from the values A keypress terminates the routine and returns to BASIC 52 org 3100h load routine above the stored values OutputPort equ 0e400h address of port to write Sine values to Begin generating the sine wave nextcycle mov 20h 0ffh store initial count at 20h in internal data memory nextvalue mov dph 30h put high byte of sine wave address 30h in dptr mov dpl 20h copy low byte of sine wave address from 20h to dptr movx a dptr place sine wave value in jacc mov dptr OutputPort copy port address to dptr movx dptr a copy Sine wave value to output port dj
162. e two more address lines on the chip Static RAM chips are rated by their read access time which is the maximum time the chip will require to place a byte on the data bus after a read is requested With a crystal frequency of 12 Mhz or lower an access time of 250 nanoseconds or less is fine for accessing external data or code memory Access times and other timing characteristics are described in the timing diagrams in the data sheets for the 8052 and RAM When you use the 8052 BASIC you don t have to worry about any of these specifics about the read and write cycles If the circuit is wired correctly and if all of the components are functioning as they should reading and writing occur automatically in the course of executing BASIC 52 statements and commands A single program line in BASIC 52 can cause dozens or more read and write operations to occur Logic families Logic chips U3 U4 and U6 are HCT family components which have TTL compatible inputs and CMOS compatible outputs This means that they can interface directly to either TTL or CMOS logic If HCT family parts aren t available there are alternatives You may use an LSTTL chip 74LS08 74LS138 74LS373 for U3 U4 or U6 Or if you use a CMOS 80C52 BASIC for U2 you may use an HCMOS 74HC08 or 74HC138 for U3 or U6 If U3 is a 74HCO08 or T4HCTO08 you may use a 75HC373 for U4 For U1 you may use a 74HC14 or 74LS14 The Microcontroller Idea Book 29 Chapter 3 Table 3
163. e 8052 s control outputs Pin 20 CST or Chip Select 1 enables U7 whenever the 8052 reads or writes to the chip with the address decoding determining the address range of the chip 28 Tne Microcontroller Idea Book Powering Up Jumper J3 chooses the chip select for an 8K or 32K device Some 8K RAMs have a second chip select CS2 which is tied high always selected by J2 If you limit yourself to either 8K or 32K RAMs you can eliminate J2 and J3 and wire the appropriate connections directly Pin 27 WE or Write Enable is driven by WRITE and is strobed low during each write to external data memory Pin 22 OE or Output Enable is driven by READ and strobes low when either external data or code memory is read With an 8K RAM each write cycle follows this sequence The 8052 brings ALE high and places the address to be written to on ADO AD7 and A8 A15 For addresses from 0 to 1FFFH A13 A15 are low so U7 is selected at its pin 20 After a short delay the 8052 brings ALE low which causes U7 to store the lower address byte After another short delay the 8052 replaces the address on ADO AD7 with the data to be written A low pulse at pin 27 WE causes the RAM to write the data into the address specified by A0 A12 Read cycles are similar except that a pulse at pin 22 OE causes the requested data to appear on ADO AD7 where the 8052 reads it With a 32K RAM the process is the same except that A15 is the chip select and there ar
164. e 880 1080 nanometers An optical filter on the photodiode blocks visible light to reduce responses to ambient light The module amplifies the detected signal and limits the peaks A bandpass filter centered on 40 kilohertz reduces the amplitude of signals outside of the range of 36 44 kilohertz A demodulator filters out the 40 kHz oscillations and recreates the original pulse pattern generated by the encoder An integrator and comparator help to ensure a clean output at VOUT The module does a good job of detecting transmitted infrared pulses at 40 kilohertz Unfortunately in spite of its optical filter it also has some response to ambient light which The Microcontroller Idea Book 205 Chapter 12 causes brief random pulses to appear at VOUT even when an IRED isn t transmitting to the module But as we Il see these random pulses are rejected by the decoder chip which looks for a specific pulse pattern to identify the transmissions intended for it To reduce false triggers on ambient light you can ground MOD1 s case by soldering a wire from pin 3 to the case You can also add more optical filtering though for this application it shouldn t be necessary Photographic film is a good inexpensive filter that passes infrared and blocks visible light Cover the photodiode s window with an exposed developed scrap of color print negative film or an unexposed developed scrap of positive color slide film The signal at pin 1 of MO
165. e digits Like the LEDs a 7 segment LCD creates a numeral by turning on selected segments Each LCD segment contains a thin layer of liquid crystal between two layers of glass Liquid crystals are organic compounds that act as electrically controlled light polarizers In a positive image display the most common type applying a voltage across a segment causes the segment to appear dark or opaque while removing the voltage causes the segment to appear light colored or transparent Negative image displays are opaque when not powered and transparent when powered By applying and removing voltages across individual segments you can display numeric alphabetic and other characters Applying a constant voltage to an LCD segment will eventually destroy it Instead you must drive the segment with an alternating voltage typically a square wave that alternately applies 5 and 5V across the segment Single digit driver Figure 8 6 shows an LCD module driven by a 4543B LCD latch de coder driver The 4543 is a lot like the 4511 LED driver with the addition of a phase input that accepts a square wave for driving the segments A typical drive frequency is around 100 Hertz A 555 timer provides the phase input or you can use any oscillator output The Microcontroller Idea Book 135 Chapter 8
166. e is that each device family has its own set of mnemonics so you have to learn a new vocabulary for each family you work with To get around this problem higher level languages like C Pascal Fortran Forth and BASIC follow a standard syntax so that programs are more portable from one device to another The idea is that with minor changes you can use a language like BASIC to write programs for many different devices In reality each language tends to develop many different dialects depending on the chip and the preferences of the language s vendor so porting a program to a different device isn t always effortless But there are many similarities among the dialects of a single language so as with spoken language a new dialect is easier to learn than a whole new language Higher level languages also simplify programming by allowing you to do in one or a few lines what would require many lines of assembly code to accomplish 8 The Microcontroller Idea Book Microcontroller Basics Interpreters and compilers are two forms of higher level languages An interpreter trans lates a program into machine code each time the program runs while a compiler translates only once creating a new executable file that the computer runs directly without re trans lating As atule interpreters are very convenient for shorter programs where execution speed isn t critical With an interpreted language you can run your program code immediately after y
167. e mode select control word selects an input or output function for both bits Mode 2 Strobed Bidirectional Bus I O is similar to Mode 1 except that data can flow both ways Mode 2 can use all of the control signals used by Mode 1 s input and output modes and is available only for Port A With Port A in Mode 2 Port B can be Mode 0 or 1 input or output The remaining three bits of Port C 0 2 can also be input or output selected with the control word 108 The Microcontroller Idea Book Switches and Keypads 7 Switches and Keypads Most microcontroller projects will include switches a keypad or some other way of allowing users to control the circuits inside The control might involve flipping a switch begin an operation pressing a key to to select an option or entering a number for the program to use in its operations For simple tasks you can use toggle slide or pushbutton switches Other projects might call for a keypad with an array of switches with each labeled with a number letter or other description This chapter shows how to add each of these to your system Simple Switches Figure 7 1 shows two single pole single throw toggle or slide switches connected to an input port Each has contacts that connect when the switch is closed and open when the Switch is open In A when the switch is open the pull up resistor brings the input high When the switch closes the input connects to ground and reads low Switch B
168. e sensor s resistance is low the input goes low You can connect this circuit to any unused pin on an input port If you use the 8052 BASIC s INT1 input you can use an ONEX1 statement to trigger a subroutine whenever the sensor detects the property in question If you use an ordinary port input reading the port bit will tell you the current state of the sensor In Figure 9 2B when the sensor switches from high to low resistance a 74LS73 JK flip flop stores the information as a high Q output which your program can read at its leisure After reading the input strobing the CLR input low brings Q low again until the next sensing event The flip flop remembers past events so you don t have to detect or respond to events as they happen MERCURY TILT SWITCH Figure 9 1 The tilt or physical angle of the mercury switch determines which of its three terminals connect The Microcontroller Idea Book 155 Chapter 9 A 5V 10K ANY INPUT PORT OR INTERRUPT PIN ORMALLY OPEN 1 OPEN eae SWI TCH SENSOR TILT VIBRATION LIGHT PROXIMITY ETC B 74L 73 FLIP FLOP 5yV ANY INPUT PORT PIN 10K ORMALLY OPEN SWITCH SENSOR TILT VIBRATION LIGHT PROXIMITY ETC L ANY OUTPUT PORT PIN PIN 12 GOES HIGH WHEN SWITCH CONTACTS CLOSE STROBE PIN 2 LOW TO CLEAR FLIP FLOP AND WAIT FOR NEXT SWITCH CLOSURE Figure 9 2 Tw
169. e this clock to time events that occur at regular intervals or as the base for clock or calendar functions Timer 1 has several uses in BASIC 52 including controlling a pulse width modu lated output PWM a series of pulses of programmable width and number writing to a line The Microcontroller Idea Book 21 Chapter 2 printer or other serial peripheral LPT and generating pulses for EPROM programming PGM PULSE Timer 2 generates a baud rate for serial communications at SER IN and SER OUT These are all typical applications for timer counters in microcontroller circuits If you don t use the optional timer functions you can program the timers for other applications In addition to timing functions where the timer increments at a defined rate you can use the timers for event counting where the timer increments on an external trigger and measures the time between triggers If you use the timers for event counting T2 T2 EX TO and T1 detect transitions to be counted The serial port The 8052 s serial port automatically takes care of many of the details of serial communications On the transmit side the serial port translates bytes to be sent into serial data including adding start and stop bits and writing the data in a timed sequence to SER OUT On the receive side the serial port accepts serial data at SER IN and sets a flag to indicate that a byte has been received BASIC 52 uses the serial port for communicating with a host
170. e to execute but with unintended results or worst of all crash the system and require rebooting BASIC 52 will detect and warn you of many programming errors If BASIC 52 detects an error when you try to run a program it will display the line containing the error along with an error message and will stop the program at that point If you get an error message examine the offending line carefully Many problems are due to syntax errors where missing or incorrect characters make it impossible for BASIC 52 to interpret the program line correctly Other times a program will run without problems but it won t do what you intended For example it s easy to forget that a hexadecimal number beginning in A F must have a leading zero or that all hexadecimal numbers must end in H Each of these BASIC 52 statements has a different result and none will produce an error message BASIC 52 Statement Resulting Action XBY 1000H 20H Writes 20H to 1000H in external data memory XBY 1000 20 Writes 14H to 3E8H in external data memory XBY 1000H 20 Writes 14H to 1000H in external data memory XBY 1000 20H Writes 20H to 3E8H in external data memory 70 Tne Microcontroller Idea Book Programming It can be hard to find an error that gives no error message The best way to narrow the search is to write and test your programs in small modules so that the amount of code to search through remains manageable The Microcontroller Idea Book 71
171. ect to this lead to pins 1 and 3 of U5 through diodes D1 and D2 Swaping the leads at pins 1 and 3 will reverse the direction of the motor Identify and wire the remaining three leads in the same way but using pins 6 7 and 8 of U5 The 5V motor is powered directly by a 5V supply This simple drive circuit is fine for many applications especially at lower speeds You can find examples of other drive circuits in the documentation from Airpax or other motor manufacturers The data sheet for the 5804B recommends adding D1 D4 to prevent problems in the logic circuits due to mutual coupling in the motor windings Schottky diodes have a smaller forward voltage drop 0 25V than other silicon diodes Resistors R1 R4 and capacitor C1 set the frequency of U4 s output To select a speed you write a number from to 15 to bits 0 3 of the output port Each bit controls one of U3 s switches For example when pin 2 of U2 is high pins 1 and 2 of U3 connect and R1 is one of U4 s timing components When pin 2 of U2 is low pins 1 and 2 of U3 are open and R1 has no effect on U4 When more than one switch is closed the parallel combination of resistors forms the timing resistance When all switches are open U4 s output is high and the motor stops In addition to the frequency of the step input motor speed depends on the step angle of your motor and the mode selected at U5 A typical motor has a step angle of 18 degrees which means that it requires
172. ectly from RAM or other memory to another device without uploading or translating to Intel Hex format The program prompts you for and stores information about the programming algorithm and addresses to program and copy from BASIC 52 s PGM instruction then uses this informa tion to program the selected locations 238 The Microcontroller Idea Book Running BASIC 52 from External Memory 14 Running BASIC 52 from External Memory Most BASIC 52 circuits use the 8052 BASIC chip with the BASIC 52 interpreter in internal ROM This is convenient but another option is to place BASIC 52 in external EPROM EEPROM or NV RAM Two reasons for doing so are to save money and to enable you to customize BASIC 52 by modifying and reassembling BASIC 52 s source file For those who want to experiment with BASIC 52 in external memory this chapter shows how to copy the BASIC 52 interpreter from ROM into NV RAM and how to design and use a system with BASIC 52 in external memory Reasons Placing BASIC 52 in external memory can save money although as prices for the 8052 BASIC chip have dropped the savings have become minimal Still if you find a good deal on 8032s or 8052s and 8K EPROMs you might find it worthwhile to build systems with these rather than using the single chip 8052 BASIC In your calculations though remember that sockets and board space add cost not to mention the extra time involved in wiring or laying out a printed circuit bo
173. edge triggered interrupts however switch bounce can cause multiple interrupts to occur with a single switch press Switch bounce occurs because manual presses of mechanical switches tend to be sloppy When you press a switch the contacts normally bounce open and closed several times before they close positively and bounce again as you lift your finger and the contacts open The computer has to be able to tell the difference between a bounce and a genuine switch press Otherwise each time you press a switch and again when you release it the computer will detect several rapid switch presses One way to handle switch bounce is to ignore keypresses that are less than a certain length usually around 10 20 milliseconds with the 112 The Microcontroller Idea Book Switches and Keypads exact value depending on the switch characteristics Ignoring switch bounce is called switch debouncing You can debounce a switch in hardware or software Because BASIC 52 is slow it has some debouncing built in When the 8052 BASIC detects an interrupt it will ignore all interrupts that occur before it exits the interrupt handling routine So if an interrupt handling routine takes 20 milliseconds to execute you probably don t need to add any debouncing circuits or delays To add additional software debouncing you can just add a delay loop like this to the interrupt routine 105 FOR I 1 TO 100 NEXT I Adjust the total count to the minimum value that preve
174. en when it receives 95 PRINT TAB 8 the gt prompt PRINT 100 LINE LINE 1 INPUT gt 0 PRINT Validating and stor ing 105 C ASC S 0 1 IF C lt gt 58 THEN GOTO 500 REM Get the byte count and save it in the variable COUNT 115 I 2 GOSUB 700 COUNT CH REM Get the starting address for this record s data 125 FOR I 4 TO 7 STEP 2 GOSUB 700 ADDR ADDR 256 CH NEXT REM Get the record type we only understand types 0 and 1 135 I 8 GOSUB 700 IF CH lt gt 0 AND CH lt gt 1 THEN GOTO 510 145 RECORD CH REM The initial checksum calculation 155 CHECK ADDR 256 ADDR AND OFFH COUNT RECORD REM Get the individual bytes accumulate them in the check sum and store REM them in memory at the appropriate destination 165 FOR I 10 TO 10 COUNT 2 STEP 2 GOSUB 700 264 The Microcontroller Idea Book Programs for Loading Files Listing B 1 page 2 of 2 REM 175 185 REM 195 205 210 215 REM 225 REM 500 510 520 525 550 555 565 600 605 REM 640 REM 700 705 Here we deal with the data bytes not executed when RE CORD is type 1 CHECK CHECK CH IF RECORD 1 THEN GOTO 210 Store the data in RAM XBY ADDR CH if CBY ADDR lt gt CH THEN GOTO 550 ELSE ADDR ADDR 1 NEXT CHECK CHECK AND OFFH IF CHECK lt gt 0 THEN GOTO 520 IF RECORD 1 THEN GOTO 640 Reset and continue ADDR 0 PRINT CR GOTO 100
175. es of short lines into fewer longer program lines when the program has to execute as fast as possible or when you need to store the program in the smallest possible space Even then though you can develop the program with short lines and combine them only after the program is debugged and ready for permanent storage e Check syntax and spelling carefully BASIC 52 s syntax consists of the rules of grammar and punctuation that your program lines must follow For example a FOR loop must include a variable limits and a NEXT instruction Leave any of these out and your loop won t work There s no room for spelling errors either BASIC 52 doesn t know that you meant LIST when you typed LSIT e Document your programs Many of BASIC 52 s keywords aren t too hard to decipher For example it makes sense that the STOP instruction halts program execution But your own comments throughout the program can help you remember why you wrote each program line and what it s supposed to accomplish BASIC 52 allows you to add comments preceded by REM remark Try to write comments that do more than just define the keywords in the line Also explain the purpose behind what you are doing For example this comment 10 REM read value from external memory 20 A XBY OFEOOH does nothing more than define the BASIC 52 instruction that follows In contrast The Microcontroller Idea Book 67 Chapter 5 10 REM Read the states of switches 1 8
176. ess of data to program 1Ah 18h High byte low byte of first address to be programmed 1 1Fh 1Eh High byte low byte indicating number of bytes to program 40h 41h High byte low byte indicating width of programming pulse High byte 65536 pulse width in seconds XTAL 12 256 Low byte 65536 pulse width in seconds XTAL 12 AND OFFh 26h For Intelligent programming set bit 3 For 50 millisecond programming clear bit 3 PHO C R Same as PRINT but displays values in hexadecimal format Uses two digits to display values less than OFFh PHO C R Same as PRINT but displays values in PHO hexadecimal format 80 The Microcontroller Idea Book Programming PHO C R Same as PRINT but outputs values in PHO hexadecimal format PH1 CR Same as PRINT but displays values in hexadecimal format Always displays four digits PH1 C R Same as PRINT but displays values in PH1 hexadecimal format PH1 CR Same as PRINT but outputs values in PH1 hexadecimal format PI CR Constant equal to 3 1415926 POP variable variable C R Assigns the value of the top of the argument stack to variable PORT1 CR Retrieves or assigns a value to PORT 1 pins 1 8 PRINT expression expression C R Displays the value of expression s on the host computer A comma at the end of the statement suppresses the CARRIAGE RETURN LINEFEED Values are separated by two spaces Additional PRINT options are CR SPC
177. esses the address bus as ports but when BASIC 52 runs from external memory the 8032 needs the address bus The Microcontroller Idea Book 241 Chapter 14 to access BASIC 52 But you can store programs in NV RAM or EEPROM using a BASIC 52 program presented later in this chapter For the external BASIC 52 system you can use the same circuits as in Figures 3 1 and 4 3 plus Figure 14 1 which adds the chip containing BASIC 52 DATA BUS DO D7 DS1225 NVRAM OR 2864 PROM OR 27 C 64 8K EPROM LOW ADDRESS BUS AQ A7 HIGH ADDRESS BUS A8 A15 AQ 1 01 Al 1 02 A2 1 03 A3 1 04 A4 1 05 AS 1 06 A6 1 07 A7 1 08 A8 26 AQ A10 ES All Al2 0 9000H 2 11 20 MRA UID CS1 ET 13 PAE 74HCT32 Hey Lal l uF PSEN ZEIGE cnoL4 8K NV MEMORY Figure 14 1 Added circuits for storing BASIC 52 in external code memory 242 The Microcontroller Idea Book Running BASIC 52 from External Memory In Figure 3 1 tie pin 31 of U2 EA to ground instead of 5V so that the 8032 boots to external memory instead of internal ROM Since you aren t using the programming functions you can eliminate some components and free up three port pins for other uses First you don t need an AND gate to combine ALE and ALEDIS so you can wire ALE U2 pin 30 directly to LE U4 pin 11 You can also eliminate R2 R9 Plus in Figure 4 3 you can elimin
178. esses to U8 until RESET goes low The delay caused by the charging of R1 through C1 in Figure 3 1 ensures that the reset algorithm has enough time to bring the port pins high U8 s Chip Select pin 20 goes low only when both of these are true RESET is low and the 8052 BASIC is reading or writing to an address from 8000h to 9FFFh Output enable pin 22 connects to RDANY to allow U8 to be accessed as data or program memory This enables U8 to store assembly language routines as well as BASIC 52 programs For writing to U8 AND gate U3C allows a choice of two control signals WRITE is the conventional signal for writing to data memory In addition BASIC 52 uses a special PGM PULSE signal to store BASIC 52 programs in NV memory beginning at 8000h Either of these signals will bring WE on U8 low 5 Tne Microcontroller Idea Book Saving Programs Jumper J4 is optional It enables you to write protect U8 by jumpering WE to 5V You might want to do this if you have critical programs or data stored in U8 and you want to be sure that you don t overwrite them accidentally Wiring Tips When you add the circuits for NV memory use sockets for U8 and U9 If you previously tied unused pins 9 and 10 of U3 to ground or 5V be sure to remove these connections before you wire the ones shown in Figure 4 3 Since pins 4 5 9 10 12 and 13 of U9 are unused CMOS inputs you should wire these to 5V or ground You may instead use a 74LS32 for U9
179. f bits 5 7 To do so follow these steps 1 Read the current value of the byte In our example with a current month of December the clock enabled and the square wave disabled register 9 will hold these values 0101 0010 2 Create a mask byte by setting all bits to be masked or unchanged to 1 and clearing the other bits To alter only the month s value bits 5 7 are masked 1110 0000 3 Logically AND the current value with the mask byte with this result 0100 0000 4 Place the new month s value in bits 0 4 of the byte To change the month to June 6th month logically OR the above byte with this 0000 0110 which results in 0100 0110 The Microcontroller Idea Book 179 Chapter 10 5 Save the result in the original location register 9 Bits 5 7 are unchanged from the original while bits 0 4 have been changed from 12 December to 6 June Listing 10 3 shows how to use the DS1286 in a BASIC 52 system It s a long program but accomplishes a lot If you don t need the alarm or another function you can shorten the program by editing out the code for it The program begins with a menu that asks you select the desired function set up and initialize display the time and date or set the alarm To initialize the clock calendar follow the prompts in the subroutine beginning at line 200 and enter the information requested The program then uses the subroutine at line 3000 to convert the information to BCD a
180. f you use a single 8K EPROM at 8000h you can use the area from AQ00h to BFFFh for additional I O Not shown are two areas that BASIC 52 reserves for optional enhancements If you customize BASIC 52 by adding your own instructions commands or reset routines BASIC 52 expects to find parameters relating to these in code memory from 200 1h to 2090h And if you want to call assembly language interrupt routines BASIC 52 expects to find vectors for these in code memory from 4003h to 41FFh For these you can use EPROM EEPROM or NV RAM as Chapter 13 shows Uses for I O Ports Just about all microcontroller circuits need to be able to do more than just read and write to memory Other uses involve sensing and controlling of conditions events or devices external to the basic circuits For example a microcontroller based drilling machine for printed circuit boards might have these responsibilities Detect when a user presses a switch Move the pc board so that the hole to be drilled lies under the drill bit Set the speed of rotation for the drill bit Lower the bit into the board then raise it after drilling Detect problems such as a bit that doesn t lower or a drilling obstruction Display messages to prompt the user for input or show progress These functions all involve reading and writing but instead of reading and writing to memory the microcontroller reads sensors and switches and writes to motors and displays Reading and writi
181. fer building their own Blue Earth Research s Micro 440e is a complete system on a tiny pc board just 1 9 x 2 25 Figure 15 3 The system uses a surface mount 83C51FB chip with both Blue Earth s version of BASIC 52 and a monitor program in ROM A case and expansion boards are also available The Micro 485 adds an analog to digital converter clock and calendar and an RS 485 interface for networking The Microcontroller Idea Book 249 Chapter 15 To speed up program execution you can use Dallas Semiconductor s DS80C520 high speed microcontrollers which are compatible with the 8051 family MDL Labs and Photronics Research offer variations of BASIC 52 designed for use with these chips BASIC 52 Source Code If you re interested in seeing the source code for the BASIC 52 interpreter look for it on Intel s or Philips BBS or on the Internet Appendix A To modify the code you ll need Intel s ASM51 or a compatible 8051 assembler 250 The Microcontroller Idea Book Sources Appendix A Sources This Appendix lists a variety of sources to help you in your 8052 BASIC projects including books on line BBS s and companies who offer products related to the topics in this book Books Here is a selection of books about BASIC 52 the 8051 2 microcontroller family and related topics BASIC 52 Essentials These are the essential hardware and software manuals for working with the 8052 BASIC You ll need either In
182. g BASIC compilers 8052 BASIC circuit boards and development software for more convenient and possibly cheaper project development Your Feedback Is Welcome This book is the result of requests from readers of my articles in ComputerCraft magazine and its successor The MicroComputer Journal l ve expanded the coverage of several topics including programming of EPROMs and other devices display options sensors and programming tips Thanks to everyone who responded to my articles with comments questions criticisms and suggestions and who in doing so helped to make this book as useful as it can be As always I welcome your comments on this work Jan Axelson 10 94 Microcontroller Basics Microcontroller Basics This chapter introduces you to the world of microcontrollers including definitions some history and a summary of what s involved in designing and building a microcontroller project What s a Microcontroller A microcontroller is a computer on a chip or if you prefer a single chip computer Micro suggests that the device is small and controller tells you that the device might be used to control objects processes or events Another term to describe a microcontroller is embedded controller because the microcontroller and its support circuits are often built into or embedded in the devices they control You can find microcontrollers in all kinds of things these days Any device that measures stores controls
183. g Basics Like other BASIC programs BASIC 52 programs are built around a set of keywords or reserved words Each keyword has a specific meaning to the BASIC 52 interpreter or example the program line PRINT XTAL tells BASIC 52 to find the stored value of the XTAL operator and send it to the console input device the serial port of the host computer which will then display the value it receives If you re familiar with BASIC programming most of BASIC 52 s keywords and conven tions will be familiar If you have little programming experience or if your experience is with assembly language C Pascal or another language you ll have more to learn But on the whole BASIC 52 makes it easy to quickly write and test your programs The Microcontroller Idea Book 65 Chapter 5 Writing a short BASIC 52 program involves these steps Define what you want to do Write program lines to accomplish it Test the results As necessary revise and retest Longer programs involve the same basic steps except that you can divide the program into a series of smaller tasks or modules and program and test each individually Then when the modules are working you can combine them in one big program and test the result Modular programming can save a lot of headaches by limiting the amount of untested program code you have to work with at one time A long untested program almost certainly contains many errors will be hard to find and fix It s much e
184. gins with an introduction to microcontrol lers and to the 8052 BASIC chip in particular Next are basic circuits to get you started programming and interfacing to the chip along with the reasons behind the component and design choices and construction details for prototyping To the basic circuits I show how to add switches keypads displays and other input output interfaces A programming reference describes each of BASIC 52 s keywords with specific tips for trouble free programming in BASIC 52 You ll also find out how to add these to your system e Sensors for detecting detect and measuring physical properties e Clock calendar functions for keeping track of seconds minutes hours days months and years and to trigger alarms at particular times e Control of AC power switch matrices stepper and continuous motors and gain of an op amp e Programmable wireless links for situations where stringing wires isn t practical or convenient viii Introduction Achapter on assembly language interfacing shows how to add assembly language programs for faster program execution how to add your own commands the BASIC 52 programming language and how to use the 8052 BASIC as a development system for an all assembly language project The final chapters cover other options for 8052 BASIC systems including how to store BASIC 52 in external memory rather than in the 8052 s internal ROM and a review of related products includin
185. have NV memory at 8000h to save MTOP If you use a 32K NV RAM from 0 to 7FFFh you should be aware that BASIC 52 reserves two areas of code memory for optional additions and enhancements One area from 2001h to 209 1h stores information that tells BASIC 52 about custom reset routines keywords and other language extensions Another area from from 4003h to 41FFh stores information about user defined assembly language interrupt routines If you won t be using these abilities you can use these areas of memory for other purposes However if at all possible it s a good idea to avoid writing to locations 2001h 2002h and 220 The Microcontroller Idea Book Calling Assembly language Routines 2048h in code memory This is because BASIC 52 checks these locations on bootup to determine what additions have been made to BASIC 52 If you by chance have certain data stored at these locations BASIC 52 will look for the additions it thinks you have and crash when it doesn t find them If you have an EPROM addressed at 8000h and you don t need the entire EPROM for BASIC 52 programs you can store your assembly language routines in the unused area BASIC 52 s F PROG command stores programs in sequence beginning at 8010h so to leave the most room for BASIC programs you should place your assembly language routines in the EPROM s highest addresses You can also add NVRAM or EPROM in any unused area of combined code data memory For exam
186. he 4 bit Interface The HD44780 s 4 bit data interface can be convenient if you don t have a lot of port bits to spare The minimum interface requires just 6 outputs to D4 D7 RS and E The drawback is that the 4 bit interface is slower in operation and more complicated to program To send an instruction using a 4 bit interface you send half at a time over D4 D7 along with the appropriate RS and R W signals D0 D3 are unused For example with an 8 bit interface writing Z SAh to the display requires the following operations clear RAW set RS write 5Ah to D0 D7 bring E high then low 148 The Microcontroller Idea Book Displays Listing 8 5 Displays key presses on the host computer s screen and on an LCD module 1 REM reserve space for 1 string variable 2 REM 1 character in length 3 STRING 3 1 4 REM You must add lines 10 through 380 of listing 8 4 5 REM to this program 400 Z 0 410 DO 420 INPUT Press a key 0 430 PRINT 0 440 REM reset display after 8 characters 450 IF Z 8 THEN Z 0 RW 0 1 1 GOSUB 900 460 REM keep track of how many characters are displayed 470 Z Z 1 480 REM display the character matching the key press 490 D ASC 0 1 GOSUB 800 500 WHILE 1 1 600 END 790 REM write data to the display 800 XBY X RS 1 810 XBY X RW 820 XBY A D 830 XBY X E 1 XBY X E 840 RETURN 890 REM write an instruction to the display 900 XBY X RS 910 XBY A I 920 XBY X E 1 XBY X E 930
187. he potentiometer in place of R8 and adjust the wiper for a 40 kHz output If you have no way to monitor U3 s frequency you can adjust R8 later by watching the receiver s response as you transmit The two inputs to NAND gate U2B are the 40 kHz oscillator and U1 s pin 15 DATA OUT When DATA OUT is high pin 6 of U2B pulses at 40 kilohertz When DATA OUT is low pin 6 of U2B is high The result is a form of modulation with the presence or absence of the 40 kHz signal representing the logic levels at the encoder s output When pin 6 of U2B is low PNP transistor Q1 switches on and current through IRED 1 causes it to emit infrared energy When pin 6 of U2B is high Q1 and IRED1 are off The result is that IRED1 pulses at 40 kilohertz when pin 15 of U1 is high and IRED1 is off when DATA OUT is low Resistor R3 limits Q1 s base current You can use any general purpose or switching PNP transistor for Q1 Resistor R4 limits the current through IRED1 to about 50 milliamperes which is high enough for basic testing If necessary you can increase the IRED s current later for increased range For best results use an IRED with a high power output Radio Shack carries high output IREDs Digi Key also has a selection including Harris FSD1QT and F5E1QT Devices with outputs at 880 or 940 nanometers are acceptable Look for a maximum continuous forward current of at least 100 milliamperes Receiver Circuits The IRED transmits the encoded ad
188. he value of a digit repeat steps 1 and 2 Displaying Messages Sometimes a device has to display more complex messages than simple LEDs and 7 segment displays can handle For example you might want to display messages like these Please enter your access code Select function Read Program Verify Exit Wind is from the west at 12 mph Total cost 5 82 With BASIC 52 you can use the host computer s display but this is no help if you want to create a stand alone project that doesn t require a personal computer In these situations a character based dot matrix LCD module is a solution These modules can display messages made up of numbers characters of the alphabet and other symbols for math functions for example or even symbols you design yourself Figure 8 8 illustrates Devices that use this type of display include laser printers and test equipment The Controller Chip A special controller chip makes it easier to use LCD modules than you might think Hitachi s HD44780 LCD controller is an 80 lead surface mount chip that takes care of the details of controlling the individual dots or segments on the display For as low as 10 you can find complete modules that contain an LCD panel and small circuit board containing the 138 The Microcontroller Idea Book Displays i i Figure 8 8 With acharacter based dot matrix LCD module you can display messages as well as numbers controller chip Applying powe
189. hertz each machine cycle is 1 microsecond and one complete cycle requires 11 microseconds multiplied by 255 points on the wave plus 6 microseconds to test the serial flag or 2811 microseconds total With different crystal frequencies the output frequency will vary in direct proportion For example with a 6 Megahertz crystal the sine wave will be half as fast To slow down the sine wave you can add do nothing instructions to the code For example adding a nop no operation instruction in the main loop will add 1 microsecond to the time between points on the wave for a frequency of 326 Hertz For long delays you can insert a timing loop that executes after each point in the wave Listing 13 5 still relies on BASIC 52 to calculate the sine values and store them in RAM Although you can also write these parts in assembly language doing so in BASIC is much easier and doesn t affect the frequency of the sine wave that results Even if you later decide to write this part in assembly language with BASIC 52 you can test each section of the code as you go along When you have your assembly language routine in the form you want it you can use Listing B 2 or an EPROM programmer to store the code in EPROM If your EPROM has different addressing than the RAM you used to test the code you must change the ORG directive in the source file to match the new location and reassemble the file before you program it into the EPROM 230 The Microc
190. host system for writing and testing programs As you are developing a project you can use a serial link to connect the host system to a target system which contains the microcontroller circuits you are testing You can then use the personal computer s keyboard video display disk drives and other resources for writing and testing programs and transferring files between the two systems The Microcontroller Idea Book 3 Chapter 1 Project Steps Putting together a microcontroller project involves several steps 1 Define the task 2 Design and build the circuits 3 Write the control program 4 Test and debug Sometimes the steps won t follow exactly in this order You may begin writing your program before you build the circuits or you may build and test some of the circuits before you start programming But however you go about it each of the above steps is part of the process To see what s involved in each step let s look at each in more detail Defining the Task Every project begins with an idea or a problem that needs a solution For example How can I monitor light intensity at different locations and times of day to find the best location for a solar collector Or how can I automate the process of drilling printed circuit boards Or how can I create a computer controlled animated display for a store window Once you know what you want to accomplish you need to determine whether or not your idea is one that requires
191. ications there is no substitute for consulting the EPROM s data sheet and following its recommendations exactly But for general use you can get reliable results with most EPROMs by using one of the two algorithms supported by BASIC 52 50 millisecond programming This algorithm is an older slower procedure To program a location in the EPROM you apply a programming voltage to the VPP input set the address and data lines to the desired values and apply a 50 millisecond programming pulse at the PGM input to write the data into the EPROM at the selected address You then increment the address apply the new data and programming pulse and continue in this way until all locations are programmed After programming you compare the EPROM s contents to the programming data to verify that all locations programmed correctly BASIC 52 varies from this standard by verifying each location immediately after programming 56 Tne Microcontroller Idea Book Saving Programs This is the recommended algorithm for older smaller capacity EPROMs like the 2 kilobyte 2716 and 4 kilobyte 2732 and some 8 kilobyte 2764s These typically require a program ming voltage of 21 or 25 volts at the EPROM s VPP input Intelligent programming This algorithm uses much shorter programming pulses and verifies after each attempt After each 1 millisecond programming pulse you read the EPROM location to see if the programming succeeded If not you try again up to 25 t
192. ich selects the chip at addresses from FCOOh to FFFFh U15 actually uses four of these addresses FCOOh through FCO3h U15 s RESET input is controlled by the same RESET signal at pin 9 of the 8052 BASIC The three new I O ports are Port A Port B and Port C Address lines AO and A1 select the port to be accessed with Port A at FCOOh Port B at FCO1h and Port C at FCO2h The port pins should connect only to voltages in the range 0 5V to 6 5V According to Intel s data sheet the 82C55 has bus hold circuits that eliminate the need for external pull ups on its CMOS inputs The Control Word You configure the 8255 by writing a control word to a control register addressed at FCO3h The control word has two functions selecting modes of operation and setting and clearing port bits When bit 7 of a byte written to the control register is 1 the control word selects modes of operation for each port and determines whether a port is input output or bidirectional Many combinations of modes and I O are available When bit 7 of a byte written to the control register is 0 the control word sets and clears individual bits of Port C The control word is write only you can t read it Mode Setting Figure 6 7 from Intel s data sheet describes the mode set control word The ports are divided into two groups Group A consists of Port A plus bits 4 7 of Port C and Group B consists of Port B plus bits 0 3 of Port C This grouping enables Ports A a
193. ille FL 32607 904 373 4629 Sensors Magazine Helmers Publishing Inc 174 Concord St P O Box 874 Peterborough NH 03458 0874 603 924 9631 Sharp Electronics Microelectronics Group 5700 NW Pacific Rim Blvd M S 20 Camas WA 98607 206 834 2500 260 optoelectronic components 8052 chips data books high speed BASIC 52 in Dallas DS87C520 8052 BASIC pc board kit 8051 assembler 8051 book Sensors Buyer s Guide optoelectronic components The Microcontroller Idea Book Siemens Components 2191 Laurelwood Rd Santa Clara CA 95054 408 980 4500 Siemens Components Optoelectronics Division 19000 Homestead Rd Cupertino CA 95014 408 257 7910 Sil Walker 880 Calle Plano Unit N Camarillo CA 93012 805 389 8100 FAX 805 484 3311 Suncoast Technologies PO Box 5835 Spring Hill FL 34606 Voice FAX 352 596 7599 Systronix 555 South 300 East Salt Lake City UT 84111 801 534 1017 FAX 801 534 1019 BBS 801 487 2778 TAB McGraw Hill P O Box 0850 Blue Ridge Summit PA 17294 0850 1 800 262 4729 Timeline Inc 1490 W Artesia Blvd Gardena CA 90247 1 800 872 8878 Unicorn Electronics 10010 Canoga Ave Unit B 8 Chatsworth CA 91311 1 800 824 3432 The Microcontroller Idea Book Sources 8052 chips data books optoelectronic components keypad kits 8052 BASIC board BASIC compiler BASIC 52 programming manual book publisher surplus LCD modules 8052 BASIC chip elec
194. imes When the location verifies you apply a final pulse equal to three times the total amount of programming pulses already applied For example if it takes five attempts to verify you would apply a final 15 millisecond pulse Finally when all locations are programmed you verify each once more For Intelligent programming VPP is typically 12 5 volts and VCC the EPROM s main power supply is also raised from 5 to 6V during programming Intelligent programming is the recommended algorithm for many 8K EPROMSs Intel s 2764 EPROM uses 21V 5 millisecond programming while the 2764A uses 12 5V Intelligent programming Quick pulse programming Some CMOS 8K EPROMs 27C64 can use an even faster programming algorithm called Quick Pulse In Quick Pulse programming VPP is typically 12 75V VCC is 6 25 and the programming pulses are 100 microseconds BASIC 52 doesn t offer Quick Pulse programming as an option Choosing an algorithm As a rule you can program an EPROM using a slower algorithm than the recommended one so you should be able to program any 12 5V EPROM with 50 millisecond programming with VPP at 12 5V and VCC at 5V And any EPROM that can use Quick Pulse programming should also program with the Intelligent or 50 millisec ond programming algorithm and voltages But whatever you do don t exceed the recom mended programming voltages for the device at VCC and VPP EPROM Pinouts Figure 4 4 shows the pinout for a 27
195. increasing H will raise it Although you can control a second motor with the 2993B you get only one PWM output on the 8052 BASIC so it s not feasible to control two motors independently in this way Figure 11 6 shows another way to control the speed of a DC motor As in Figure 11 4 the circuit uses a 4066B quad analog switch to select a timing resistance for a 555 timer Varying the timing resistance varies the duty cycle of the 555 s output and thus the motor s speed You can select timing resistances that result in the motor speeds you want The values shown will vary the duty cycle from about 90 to 20 percent The Microcontroller Idea Book 197 Chapter 11 Four output bits of an 82C55 set the motor speed Additional bits set the direction of rotation and turn the motor on and off by controlling the 555 s RESET input You can use any output port bits to control the motor but logic high inputs at the 4066B must be at least 3 5V so if you use NMOS or TTL outputs add a 10K pull up resistor from 5V to each port output that connects to the 4066B Listing 11 5 asks you for a motor speed and direction then causes the motor to spin as directed 198 The Microcontroller Idea Book Wireless Links 12 Wireless Links Wires and cables are by far the most common way to connect one circuit to another but wireless links are another option Sometimes a wireless connection is more flexible convenient or practical because you d
196. ine pacing can be 0 In the Windows terminal select Settings then Text Transfers One Line at a Time and enter gt under Wait for Prompt String Other software should have similar abilities If you wish you can use BASIC 52 s F PROG command to store the program in NV memory so it s available without having to upload each time To use Listing B 1 or B 2 run the program and at the prompt use your communications software to upload your object file The file will load into the locations specified by your source file The program will display error messages if it has problems with the uploading For proper calculation of the programming pulse width in Listing B 2 set BASIC 52 s XTAL operator to match your crystal s frequency If the file loads successfully you re ready to test it Connect a logic probe to pin on the 8052 or set a voltmeter to measure the voltage from pin to pin 20 ground on the chip To call your subroutine enter and run this BASIC 52 program The Microcontroller Idea Book 225 Chapter 13 10 CALL 3000h 20 END If necessary change the address in line 10 to match the value in your routine s org directive Each time you run the program you should see pin 1 on the 8052 change from high to low or low to high The routine should then return you to the BASIC 52 prompt If the program crashes and does not return you to BASIC 52 you need to re examine your listing file to see what went wrong Re
197. ined by BASIC 52 You also can t name a variable MONTH ONE ACTION or any other word that contains ON Short variable names are much less likely to contain an embedded keyword Also be aware that BASIC 52 identifies a variable only by its first and last characters plus its length so for example it considers MAXIMUM and MINIMUM to be the same variable while MAX and MIN are different e Avoid variables that begin or end with the letter F BASIC 52 has a couple of bugs relating to variable names that begin or end in F Specifically when F is the last character in a variable name followed by a space BASIC 52 drops the F from the variable name And if you should name a variable FP FPR or FPRO and follow the name by a space BASIC 52 will also drop the F from the name The easiest way to avoid problems is to avoid any variable name that begins or ends in F 68 The Microcontroller Idea Book Programming e Hexadecimal numbers that begin with A through F must have a leading 0 and all hexadecimal numbers must end in H Here are some examples of valid hexadecimal numbers Valid Hex Number Decimal Equivalent ODH 208 OAH 10 15H 21 OFFFFH 65 535 OCH 12 Here are some invalid hex numbers and a valid hex number that doesn t have its intended value Invalid Hex Number Problem FFH no leading 0 oC no trailing H 10 intended as decimal 16 no trailing H BASIC 52 will interpret at decimal 10 OAH BASIC 52 Bugs and Thi
198. ing As you can see not every sensor has an output that can connect directly to the ADC0848 s inputs A sensor s output may vary from 2 to 1V from 0 5 to 0 5V or from 12 to 12V In all of these cases you need to shift the signal levels and sometimes adjust the signal range to be compatible with a converter that requires inputs between 0 and 5 volts Figure 9 9 shows a general purpose circuit that can amplify or reduce input levels and can also raise or lower the entire signal by adding or subtracting a voltage Separate independent adjustments control the gain and offset The circuit is a series of three op amps a buffer a level shifter and an amplifier The example circuit uses three of the devices in an LF347 quad JFET input op amp The LF347 has fast response and high input impedance You may use a different op amp if you prefer The first op amp is a noninverting amplifier whose output at pin 1 equals VIN The op amp presents a high impedance input to VIN to minimize loading effects The second op amp is an inverting summing amplifier that shifts pin 1 s voltage up or down as R5 is adjusted Adjusting R5 raises and lowers the voltage at pin 7 but the signal s shape and peak to peak amplitude remain constant The third op amp is an inverting amplifier whose gain is adjusted by R4 This amplifier increases or decreases the peak to peak amplitude of its input The Microcontroller Idea Book 167 Chapter 9 fe E
199. ion The Microcontroller Idea Book 145 Chapter 8 Listing 8 4 page 1 of 2 Initializes a 2 line LCD module and displays a message on each line 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 146 REM address A 0FC00H REM address C A 2 REM address X A 3 REM Control E 0AH REM Control RW 0CH REM Control RS 8 REM Initial REM initial XBY X 80H XBY X E XBY X RW XBY X RS REM function set of 8255 Port A of 8255 Port C of 8255 Control port word for Enable PC 5 word for RW PC 6 word for RS PC 4 ize LCD module values REM Ports A B amp C are outputs REM E 1 REM RW 1 REM RS 1 8 bit interface 3 times REM toggle E after each instruction XBY A 30H XBY X E 1 XBY X E XBY A 30H XBY X E 1 XBY X E XBY A 30H XBY X E 1 XBY X E REM function set to match module XBY A 38H XBY X E 1 XBY X E REM display XBY A 0CH on XBY X E 1 XBY X E REM clear d XBY A 01H isplay XBY X E 1 XBY X E REM entry m XBY A 06H ode set XBY X E 1 XBY X E The Microcontroller Idea Book You download this file from web site http www pcports ru Displays Listing 8 4 page 2 Of 2 390 REM display LINE 1 LINE 2 400 D ASC L GOSUB 800 4
200. isting 13 2 Listing file created by assembling the source file in Listing 13 1 3000 org 3000h location where program will load in RAM 3000 b2 90 cpl pl O complement Port 1 bit 0 pin 1 3002 22 ret return to BASIC 52 222 The Microcontroller Idea Book Calling Assembly language Routines Figure 13 1 Examples of a byte expressed in binary hexadecimal and the ASCII codes representing the Hex characters Binary value 1100 0101 Hex equivalent C 5 ASCII code for Hex character 43 35 common formats are binary ASCII Hex and Intel Hex Intel Hex is also the format required for programs that you upload using Listings B 1 and B 2 Figure 13 1 shows a byte expressed in binary hexadecimal and ASCII hex Binary A binary file is the most primitive or unadorned type It consists of a sequence of bytes that exactly corresponds to the bytes to be programmed The file contains no addressing information for loading or programming and no error checking To view or edit a binary file on a personal computer you need a special file viewing utility This is because conventional file viewing techniques such as MS DOS s TYPE command will interpret the bytes as ASCII codes and will display the ASCII characters that the codes represent For example the value 1 in a binary file appears on screen as a happy face character ASCII Hex In ASCII Hex or pure Hex format each byte is expressed as a 2 character hexadecimal number w
201. isting 3 6 This program will end only when the user presses cConTROL Cc 10 CLOCK 1 TIME 0 SEC 0 20 DO 30 ONTIME 1 100 40 WHILE 1 1 50 END 100 TIME TIME 1 110 PHO PORT1 120 RETI 44 Tne Microcontroller Idea Book Powering Up Listing 3 7 This program ends when inTt pin 13 is brought low and causes an interrupt routine to execute 10 CLOCK 1 TIME 0 SEC 0 20 A 0 30 PRINT Bring INT1 pin 13 low to end program 40 DO 50 ONTIME 1 100 60 ONEX1 200 70 WHILE A 0 80 END 100 TIME TIME 1 110 PHO PORTL 120 RETI 200 A 1 210 RETI doesn t equal zero it means that a key was pressed In Listing 3 5 when GET no longer equals 0 the program ends Wait for CONTROL C You can always end a program by pressing CONTROL4C at the host s keyboard The only exceptions are runaway programs that have crashed the system and force you to reboot Listing 3 6 is an expanded version of Listing 3 5 It continues to read and display PORT1 in an endless loop DO WHILE 1 1 until you press CONTROL C Detect a Switch Press A final method will end a program without any input from the host s keyboard You can use this in stand alone projects that don t connect to a host computer at all Listing 3 7 ends when the 8052 BASIC s pin 13 ANTT goes low which causes an interrupt routine to execute Bring the pin low by jumpering it briefly to GND or connect a pushbutton switch as described in Chapter 7 The Microcont
202. ith each character represented by its ASCII code ASCII Hex files contain only these 16 codes 30h through 39h for numerals 0 through 9 and 41h through 46h for capital letters A through F You can easily view and edit ASCII Hex files on a personal computer because the computer displays the ASCII characters that the codes represent However the EPROM programmer or uploading program must translate the codes into binary data before it writes the codes into the device to be programmed Because each byte to be programmed requires two codes an ASCII Hex file is twice as long as the resulting file that is programmed into the EPROM Listing 13 3 Intel Hex file created by assembling the source file in Listing 13 1 gt 03300000B2902269 00000001FF The Microcontroller Idea Book 223 Chapter 13 Intel Hex Like ASCII Hex Intel Hex format stores bytes as ASCII codes representing hexadecimal characters But Intel Hex adds addressing and error checking information for more flexible programming and more reliable file transfer Each Intel Hex file consists of a series of records Table 13 1 has more details about the records and what they contain You don t have to understand everything about Intel Hex format in order to use it but the information can be useful if you run into problems and want to examine the contents of a file Assembling a Program When you assemble a program the message Assembly Successful or something similar means
203. l eight displays connect to the 7218D s segment driver outputs a g dp Each display s common cathode connects to one of eight DIGIT outputs An internal oscillator 132 The Microcontroller Idea Book Displays 1CM7218D 8 DIGIT MULTI PLEXED 82 C 55 LED DRIVER PA HIDO a PA 1 bs 73 0 b PA 2H wile c PAs Sg 1103 d PA 4 1D7 e f PAS 1DAQ J PA 6 s DA DECIMAL PA 7 1 lDA2 POINT DIGIT 1 pc 4H3 SIWRITE DIGIT 2 5V DIGIT 3 al DIGI USE ANY lo MODE DIGIT 5 PORT OUTPUTS V DIGIT 6 TO CONTROL 28 GNb DIGIT 7 1CM7218D DIGIT 8 ID 1D3 SELECT DIGIT 8 7 ID7 CONTROLS DECIMAL POINT PIN 9 MODE HIGH HEX Q 123456789ABCDEF OPEN CODE B Q 123456789 EHLP LOW SHUTDOWN OFF Figure 8 5 The 1ICM7218D can control up to eight 7 segment LEDs turns on each of the digits in sequence This means that each of the displays is on just 1 8 of the time The 7218D drives each segment at 20 milliamperes peak current for an average current of just 2 5 milliamperes The chip takes advantage of the fact that LEDs can withstand relatively high pulsed currents and that a pulsed LED actually appears brighter than a constantly driven LED with the same average current Twenty milliamperes is well within the allowed
204. l pl o complement Port 1 bit 0 pin 1 pop psw push psw was automatic on interrupt but pop psw must be added reti end and add this to the end before returning to BASIC 52 pop psw restore program status word Your routine can then write to registers RO R7 without worrying about conflicting with BASIC Interrupts BASIC 52 also includes a way of adding assembly language routines that respond to interrupts Normally the 8052 stores its interrupt vectors the locations where the program jumps on interrupts from 03h to 2Bh in code memory Since these locations are in ROM in the 8052 BASIC your programs can t change their contents But built into BASIC 52 is the ability to place alternate interrupt routines from 4003h to 402Bh To illustrate Listing 13 6 is an assembly language interrupt routine The routine s origin is 4013h which is BASIC 52 s alternate vector for external interrupt 1 The interrupt routine has the same function as Listing 13 1 It toggles bit 0 of Port 1 then returns to BASIC 52 These are a few things of note about Listing 13 6 e You must have code memory at 4013h since BASIC 52 specifies that this location must contain either the interrupt routine or a jump to a longer routine If the routine is longer than 8 bytes use a jump instruction such as sjmp 4033h to prevent overwriting any interrupt vectors that follow 232 The Microcontroller Idea Book Calling Assembly language Routines e
205. latches that store logic states 26 The Microcontroller Idea Book Powering Up 74HCT 138 3 TO 8 LINE DECODER INPUTS OUTPUTS ENABLE SELECT G1 G2AG2B C B AJ Y YI Y2 Y3 Y4 Y5 Y6 Y7 L X X X XX IH H H HHHHH X SHOE IX XX SILAS H H A Ce As CH H X X H X X X H H H H H H H H H L ji K L L L H H l H i H O H L L L L H H L H H H H H H H L LIL H L H H L H H H H H H L LIL H H H H L H H H H H L LIJH tL BoA H H H E H H H H L LIH L H H H H H H LH 4 H L L H H L H H H H H L H L L H H H H H H H H H H L 74HCT373 OCTAL TRANSPARENT LATCH OUTPUT LATCH CONTROL enaBLE PATAJ OUTPUT Oc LE 1D 8D 10 80 L H H H L LOGIC LOW L H L A H LOGIC HIGH L L X CHANGE X DON T CARE H x x Z Z HIGH IMPEDANCE Figure 3 2 Truth tables for the 74HCT138 decoder and 74HCT373 octal transparent latch A latch enable input LE controls whether the outputs are latched stored or not latched immediately follow the inputs Figure 3 2 shows the truth table for the chip When pin 11 is high 1Q 8Q follow 1D 8D When pin 11 goes low outputs 1Q 8Q will not change until pin 11 goes high again During each external memory access 1Q 8Q store the low address byte so the eight lines that connect to these outputs carry the label LOW ADDRESS BUS AND gate U3B latches or stores U4 s outputs only when both ALE and ALED
206. le e To minimize noise in the oscillator circuits place XTAL1 C2 and C3 close to pins 18 and 19 of U2 and connect them with short wires Wire the ground terminals of C2 and C3 directly to pin 20 of U2 e When you wire the following components correct orientation is required C1 C4 C8 D1 LED1 and U1 U7 Figure 3 4 shows common polarity indicators for these components Notice that C7 s positive terminal connects to ground and C6 s negative terminal connects to 5V since these capacitors connect to the MAX232 s 10V and 10V outputs e As you wire the circuits remember that everything on the wire wrap or solder side of the board is a mirror image of the way it looks on the component side of the board If pin 1 is in the upper left corner on the component side it s in the upper right corner on the wire wrap side assuming that you flip the board over from side to side not top to bottom e Labels on the wire wrap side are helpful You can place a dot of indelible ink near pin 1 or adhesive labels between the pins or use prelabeled and punched plastic labels that slide onto the wire wrap pins The Microcontroller Idea Book 33 Chapter 3 TD DATA OUT RD DATA IN SIGNAL GROUND SGND O2 RS232 OUT U5 PIN 14 OS RS23 2 IN U5 PIN 13 RD DATA IN TD DATA OUT SIGNAL GROUND SGND OS GND U5 PIN 15 9 PINS MALE PIN CONNECTOR EMA SOCKET CONNECTOR HOST COMPUTER TARG
207. link s 207 powering up 35 PPI 98 108 printed circuit boards 248 249 Procomm Plus 36 BASIC 52 s 72 86 reset 22 26 ROM about 7 in 8052 17 ROM command 54 RS 232 30 34 35 run mode 66 S sample and hold 169 SBC 3 schematic reading 31 system 24 30 sensors 153 170 serial port 8052s 22 RS 232 30 34 35 7 segment display 129 138 simulator 10 sine wave generator 226 229 single board computer 3 single stepping 10 SmartSocket 48 49 software for uploading programs 221 terminal emulation 15 solar cell 165 166 source code BASIC 52 250 stack 231 stepper motor 191 195 subroutines 66 67 switch matrix 187 189 power 185 187 press detecting 45 sensor as 155 toggle and slide 109 115 T target system 3 task defining 4 5 temperature sensor 163 165 Terminal Accessory Windows 36 terminal emulation 15 test equipment 16 timekeeper watchdog 174 184 timers and counters in 8052 21 use of 171 184 transducer 153 troubleshooting 9 10 37 70 71 TTL compatible logic 29 Index V vendors 255 262 W watchdog timekeeper 174 184 Windows terminal accessory 36 wireless link 199 216 WR 21 write cycle 29 signal 21 to a port 97 X XFER 54 XTAL 38 See also crystal 277 Index 278
208. load the resulting Intel Hex file into NV memory that will be preserved on powering down or rebooting Reboot and you can use the new keywords TGGP10 SETP10 and CLRP10 to control bit 0 of Port 1 Notice that the bit toggle keyword is TGGP10 rather than TOGP10 which contains the keyword TO and so won t work The Microcontroller Idea Book 235 Chapter 13 Listing 13 8 page 1 of 2 Copies data from external memory into EPROM EEPROM or NV RAM 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 236 PRINT enter device type PRINT EPROM 50 msec a PRINT EPROM Intelligent 2 PRINT EEPROM or NV RAM 3 PRINT quit 4 INPUT T REM set pulse width for device type REM W pulse width in milliseconds IF T 1 THEN W 05 IF T 2 THEN W 001 IF T 3 THEN W 0005 IF T 4 THEN GOTO 470 REM calculate and store pulse width B 65536 W XTAL 12 GOSUB 500 DBY 40H BH DBY 41H BL REM set up for intelligent programming or not I DBY 26H IF W 001 THEN DBY 26H I OR 8 ELSE DBY 26H I1 AND O0F7H INPUT starting address of data to copy source S IF S lt 200H OR SSOFFFFH THEN GOTO 190 INPUT ending address of data to copy source E IF E lt S OR ESOFFFFH THEN GOTO 210 INPUT starting address to program destination P IF P lt MTOP OR PSOFFFFH THEN GOTO 230 REM calculate and st
209. lso use a kit or assembled board as a base if you wish Choosing a chip Does it matter which microcontroller chip you use All microcontrollers contain a CPU and chances are that you can use any of several devices for a specific project Within each device family you ll usually find a selection of family members each with different combinations of options For example the 8052 BASIC is a member of the 8051 family of microcontrollers which includes chips with program memory in ROM or EPROM and with varying amounts of RAM and other features You select the version that best suits your system s requirements Microcontrollers are also characterized by how many bits of data they process at once with a higher number of bits generally indicating a faster or more powerful chip Eight bit chips are popular for simpler designs but 4 bit 16 bit and 32 bit architectures are also available The 8052 BASIC is an 8 bit chip Power consumption is another consideration especially for battery powered systems Chips manufactured with CMOS processes usually have lower power consumption than those manufactured with NMOS processes Many CMOS devices have special standby or sleep modes that limit current consumption to as low as a few microamperes when the circuits are The Microcontroller Idea Book 5 Chapter 1 inactive Using these modes a data logger can reduce its power consumption between samples and power up only when it s time to take
210. ltages As with EPROMs the number of erase program cycles is limited The 8052 BASIC uses two types of program memory An 8 kilobyte or 8K on chip ROM stores the BASIC 52 interpreter For storing the BASIC 52 programs that you write the BASIC 52 language has programming commands that enable you to save programs in external EPROM EEPROM or NVRAM Other memory Most systems also require a way to store data for temporary use Usually this is RAM whose contents you can change as often as you wish Unlike EPROM ROM EEPROM and NVRAM the contents of the RAM disappear when you remove power the chip unless it has battery back up Most microcontrollers include some RAM typically a few hundred bytes The 8052 BASIC has 256 bytes of internal RAM Acomplete 8052 BASIC system requires at least 1024 bytes of external RAM as well T O options Finally input output I O requires design decisions Most systems require interfaces to things like sensors keypads switches relays and displays Most microcon The Microcontroller Idea Book 7 Chapter 1 trollers have ports for interfacing to the world outside the chip The 8052 BASIC uses many of its ports for accessing external memory and performing other special functions but some port bits are available for user applications and you can easily increase the available I O by adding support chips Writing the Control Program When it s time to write the program that controls your project
211. lues decrease the oscillator s start up time while larger values increase stability Reset circuit A logic high on pin 9 of U2 resets the chip On power up pin 1 of U1 rises slowly from OV to 5V as capacitor C1 charges through resistor R1 Inverter U1 has a Schmitt trigger input which has upper and lower switching thresholds that help to ensure a clean reset pulse at pin 9 of U2 On a logic gate that doesn t have a Schmitt trigger input the output may oscillate if a slowly changing input remains near the switching threshold In contrast at Ul when pin 1 reaches the upper switching threshold about 2 8V pin 2 switches from high to low but won t go high again until pin drops to the lower threshold of about 1 8V Pressing and releasing S1 resets the 8052 BASIC chip by discharging C1 and then allowing it to recharge which brings RESET high then low again External Memory The remaining connections to U2 have to do with reading and writing to external memory Read and write signals To enable reading combined program and data memory AND gate U3A s output is RDANY This signal is low when either READ or PSEN is low Figure 3 1 s circuit doesn t use RDANY but I ve included U3A for future use Writing to data memory is controlled by WRITE Code memory can t be written to ADO AD7 connect to U4 a 74HCT373 octal transparent latch that stores the lower address byte during memory accesses The chip contains a set of D type
212. ly tolerance in other words ones that are guaranteed to operate from supplies of 4 5 to 5 5V You do want to be sure that your main supply is a solid 5V or even a little higher The data sheets for some EPROMs specify 5 percent tolerance the supply must be between 4 75 and 5 25V to guarantee operation within the specifications In this case you will be operating near or just below the recommended supply voltage especially if your main supply is slightly under 5V When you are not programming the EPROM you can move J6 to connect pin 28 directly to 5V But overall 10 percent tolerance EPROMs are a better choice for this circuit If you are using a NVRAM or EEPROM set J6 to 5V since VCC must remain at 5V for these devices Power Supplies for Programming You have several options for creating the programming power supplies of 12 5V and optionally 6V Benchtop Supply For occasional use if you have a benchtop supply that can supply the needed outputs you can add terminals to the appropriate connections in your BASIC 52 system and connect the supply leads to them when needed Adjustable Regulator Figure 4 6 shows a circuit that regulates a DC supply of 15 to 18V to 12 5V or 6V For the 15V supply you can use a benchtop supply a wall transformer AC to DC adapter or even two 9 volt transistor batteries connected in series The supply must have a DC output but it doesn t have to be regulated You ll need one LM317 and an
213. m resistance decreases as the foam is pressed A popular homemade moisture detector is a printed circuit board with two interleaved but untouching copper traces When the board is wet water shorts the traces together and changes the resistance between them from very high to a few hundred ohms Some projects call for a specialized sensor that you just won t find in the usual sources A good resource is the Sensors Buyer s Guide published annually by Sensors magazine The guide lists over 1200 companies involved with sensors and indexes them according to property sensed technology used manufacturer and related products and services From the list of properties sensed you can select the category that interests you and consult a list of companies that offer products in that area Most companies are happy to provide product information and applications hints Choosing Sensors To pick the right sensor for a job you first need to specify what you want the sensor to do Below are some of the questions to ask about your desired sensor The example answers describe a temperature sensor intended for use in a controller used in processing photo graphic film e What property do I want to measure temperature e What range of inputs do I need to measure 60 110 degrees Fahrenheit e What resolution and accuracy do I need accurate to within 0 5 degree Fahrenheit e How fast must it respond to input changes quick response not critical for this
214. member that the address in BASIC 52 s CALL 12V 9 120 7 27 GarReB VCC 5 TO S U 1 OK OUTPUT 4 DAC8 32 PORT Fae 1 1K 2 0 16 p4 OUT I E400H 205 Fa e U D6 1OUT2 REFERENCE 317 VOL TAGE 5VO 4 ILE VREF s E CS 2 WRI 18 WRZ 17 VEER GND GND 3 1te ae DIGITAL TO ANALOG CONVERTER Gvd T i AO LES53 AX FILTER BOTTOM VIEW sE LM385 2 5 VOUT Figure 13 2 By writing the appropriate values to an output port you can cause a sine wave to appear at vour 226 The Microcontroller Idea Book Calling Assembly language Routines statement must match the address in your file s org directive A missing ret instruction in the routine will also cause the system to crash Example Creating a Sine Wave When you have the simple routine working you re ready to move on to bigger things For the sine wave project we ll begin by generating a sine wave entirely with BASIC 52 statements This way we can first test the added circuits as well as the algorithm or sequence of steps that we plan to use to generate the sine wave It also illustrates the speed limits of BASIC 52 The Circuits Figure 13 2 shows the circuit that interfaces to the 8052 I adapted the circuit from an example in National Semiconductor s data sheet for the DAC0832 U1 is a DAC0832 digital to analog converter or DAC which converts da
215. n alarm REM time of day alarm is edge triggered low going INTA XBY WT 0BH OD8H DO ONEX1 3200 WHILE 1 1 RETURN REM convert decimal to BCD X INT X 10 16 X INT X 10 10 RETURN REM convert BCD to decimal X INT X 16 10 X 16 INT X 16 16 RETURN REM alarm interrupt routine PRINT ALARM GOSUB 1000 RETI The Microcontroller Idea Book Control Circuits 11 Control Circuits This chapter presents a variety of ways to use an 8052 BASIC system for computer control The applications include switching power to a load controlling a matrix of switches selecting the gain of an op amp and controlling speed and direction of stepping and dc motors Switching Power to a Load You can use your 8052 BASIC system s port bits to control power to all kinds of devices including those powered by alternating current AC or direct current DC at voltages other than 5 volts Figure 11 1 shows two port bits that control solid state relays that switch power to AC and DC loads A solid state relay is a simple safe way to switch power to devices that require high voltages or currents A logic voltage at the relay s control inputs determines whether or not power is applied to the load In a typical solid state relay the control voltage is electrically isolated from the switching circuits which contain an optoisolated triac or a similar device Many AC solid state relays include zero switching circuits which reduce
216. n displaying the next value in the PRINT statement Example PRINT TAB 5 hello hello 84 The Microcontroller Idea Book Programming PRINT TAB 2 hello hello TAN expression C R Returns the tangent of expression TCON C R Retrieves or assigns a value to the 8052 s special function register TCON TIME C R Retrieves or assigns a value in seconds to BASIC 52 s real time clock TIMERO C R Retrieves or assigns a value to the 8052 S special function registers THO and TLO TIMER1 CR Retrieves or assigns a value to the 8052 s special function registers TH1 and TL1 TIMER2 CR Retrieves or assigns a value to the 8052 s special function registers TH2 and TL2 TMOD CR Retrieves or assigns a value to the 8052 s special function register TMOD U PRINT option Same as USING UIO C R Restores BASIC 52 s console input driver after using UI1 UI1 C R Allows a user provided assembly language console host computer input routine to replace BASIC 52 s console input driver External program memory location 4033h must contain a jump to the user s routine UOo0 C R Restores BASIC 52 s console output driver after using UI1 vol C R Allows a user provided assembly language console host computer output rou tine to replace BASIC 52 s console output driver External program memory loca tion 4030h must contain a jump to the user s routine The Microcontroller Idea Book 85 Chapter 5
217. n single bits of data rather than a byte at a time Options for storing programs Another consideration in circuit design is how to store programs Instead of using disk storage most microcontroller circuits store their programs on chip For one of kind projects or small volume production EPROM has long been the most popular method of program storage Besides EPROMs other options include EEPROM ROM nonvolatile NV or battery backed RAM and Flash EPROM The program memory may be in the microcontroller chip or a separate component To save a program in EPROM you must set the EPROM s data and address pins to the appropriate logic levels for each address and apply special programming voltages and control signals to store the data at the selected address The programming process is sometimes called burning the EPROM You erase the contents by exposing the chip s quartz window and the circuits beneath it to ultraviolet energy Some microcontrollers contain a one time programmable or field programmable EPROM This type has no window so you can t erase its contents but because it s cheaper than a windowed IC it s a good choice when a program is finished and the device is ready for quantity production 6 The Microcontroller Idea Book Microcontroller Basics Several techniques are available for programming EPROMs and other memory chips With a manual programmer you flip switches to toggle each bit and program the EPROM byte
218. ncrease the length of the link are by increasing the power of the transmitted signal and by focusing the signal more precisely on the receiver About Infrared Energy But first some basics about infrared Like visible light infrared energy is a form of electromagnetic radiation Infra means below and infrared frequencies are just below those of red light Infrared frequencies are invisible or beyond the range detected by the human eye Since wavelength is the inverse of frequency infrared wavelengths are longer than those of visible light Visible light covers the range 400 700 nm nanometers while infrared includes 700 nm through 1 million nm 400 nanometers is 0 4 micron or 4000 angstroms Infrared emitting diodes or IREDs are low cost widely available sources of infrared energy An IRED is a semiconductor diode that emits infrared energy when a forward current passes through it much as an LED emits visible light 212 The Microcontroller Idea Book Wireless Links IREDs emit energy at specific wavelengths Two popular types are GaAs gallium arsenide at 940 nm and GaAlAs gallium aluminum arsenide at 880 nm These are both in the range known as near infrared to signify that their wavelengths are close to the visible spectrum Infrared detectors are also specific in the wavelengths they detect although most will respond over a range For example the Sharp GP1U52X receiver module is most sensitive at 980 nm but will also
219. nd stores the result in the appropriate register of the DS1286 When all of the information has been entered line 470 starts the clock by bringing bit 7 of register 9 low Line 1000 begins the subroutine to display the current time and date Before reading from the DS1286 the program clears TE transfer enable register B bit 7 This freezes the registers at their current values and allows you to read the complete time and date information without errors If you don t freeze the registers if one of them updates in the middle of a series of read operations you could end up with an invalid time or date For example if you read the hour just before 10 00 and read the minutes just after 11 00 you will think that it is 10 00 when it is really 11 00 Freezing the registers ensures that you will read the value of all of the registers as they were when TE went low Freezing the registers does not stop the clock however The DS1286 continues to keep track of the time and when you bring TE high again the chip updates the registers to the current time and date After the program freezes the registers it reads the values from the DS1286 uses a subroutine at line 3100 to convert them from BCD to decimal and displays the results Finally the program sets TE to update the registers A subroutine at line 2000 handles the third function of the program setting the alarm To use this routine you must wire pin 1 of the DS1286 INTA to pin 13 of the
220. nd B to each use half of Port C for handshaking or control signals To set the mode bit 7 of the control word must be 1 Bit 2 selects mode 0 or 1 for Group B and bits 5 and 6 select mode 0 1 or 2 for Group A Bits 0 1 3 and 4 select whether a port is input or output with each half of Port C selected independently The simplest mode is Mode 0 Basic Input Output The ports behave very much like the inputs and outputs at U12 and U14 Outputs are latched so they change only when written to The inputs are not latched so the present or current value of the input is always read This statement configures all ports as inputs in mode 0 The Microcontroller Idea Book 103 Chapter 6 CONTROL WORD D7 D6 D5 D4 D3 D2 D1 Da GROUP B PORT C LOWER gt l INPUT OUTPUT PORT B l INPUT OUTPUT MODE SELECT gt MODE l MODE J GROUP A PORT C UPPER gt l INPUT OUTPUT PORT A N 1 INPUT O OUTPUT MODE SELECT gt QQ MODE l MODE IX MODE 2 X MODE SET l ACTIVE Figure 6 7 With bit 7 set writing to the 8255 s control word selects the modes of operation for each port 104 Tne Microcontroller Idea Book Inputs and Outputs XBY OFCO3h 9BH On reset the 8255 uses this mode until you tell it differently To read P
221. ne LINE PGM error at address 3070 ADDR DBY 1AH 256 DBY 18h PHO 3080 PHO The byte at address is XBY ADDRESS 3090 PHO The byte should be DBY 28 END 3100 PHO CR Line LINE Error writing at address ADDR 3110 PHO The byte at addr is XBY ADDR 3120 PHO The byte should be XBY I END REM verify CBY read in RAM failed 3130 PHO The byte at addr failed a verify with CBY END The Microcontroller Idea Book END 269 270 The Microcontroller Idea Book Number Systems Appendix C Number Systems Designing and programming microcontroller circuits often involves working with different number systems including hexadecimal and binary as well as familiar decimal numbers Hexadecimal and binary systems are useful because they offer an easy to interpret way of expressing the bit and byte oriented values that computers use This appendix is a review of these number systems About Number Systems A number system provides a way to express numerical information Each of the number systems described below varies in the number or quantity on which it is based 10 2 or 16 This determines among other things how many characters you need to express a given quantity Decimal Numbers In the decimal number system used in everyday non computer life there are ten digits 0 9 Each digit in a number represents a value raised to
222. nel and second an inverter module to provide the high voltage alternating signal required to power the panel The inverters typically convert 5 volts to around 100 volts RMS at 400 Hertz Inverters are usually offered along with the modules that use them so you shouldn t have to construct your own The backlighting requires several milliamperes Incandescent and LED backlights are other options for illuminating LCDs Inside the Display Controller The HD44780 LCD controller is actually a small specialized microcontroller in itself It contains its own RAM and ROM and executes the 11 instructions shown in Table 8 2 The instructions perform tasks like clearing the display writing a character to the display selecting a position on the display and reading information from the display To use the controller you need to be familiar with what it contains and the instructions that control it 140 The Microcontroller Idea Book Displays Table 8 1 LCD modules containing the HD44780 controller often use this 14 line interface Pin Symbol Input Function Output 1 VSS Input Signal Ground 2 VDD Input Supply Voltage 5V 3 vo Input Contrast adjust 4 RS Input Register select 1 data O instruction register busy flag address counter 5 R W Input Read 1 write 0 select 6 E Input Enable 7 DO 1 0 Data bit 0 8 D1 VO Data bit 1 9 D2 VO Data bit 2 10 D3 1 0 Data bit 3 11 D4 V O Data bit 4 12 D5 VO Data bit 5 13 D6 1 0 Data bit
223. nes RED I SA yr lpg 11 91K H yes RS 1 KHZ IE REMOTE CONTROL ENCODER E TIMING COMPONENT SET Al A5 TO MATCH RECEIVER S ADDRESS CALCULATIONS SET D6 D9 TO DESIRED DATA TO TRANSMIT COS Oi Be es oes 2 3 RI C2 IKHZ lt F lt 4QQKHZ R2 gt 2 R1 20K lt R2 lt IM EE 1Q K lt RI lt IM F U3 400pF lt C2 lt 15uF 3V C5 R7 2 R8 P u R7 4 ls 5V 3 6K y RS i 7 p DIS 4 KHZ OUT i OUT gt 40KHZ OUT R 74HCT132 ie TLC555 P 5 R5 eoe CTRL 10M HRESH XTAL1 R6 GND 4QKHZ 100K m ER es l 4166 ze i a H 4 Q Q1 ur T 22pF lp 22pe 4QKHZ OSCILLATOR 1 4 KHZ OSCILLATOR 2 Figure 12 1 This infrared transmitter sends 4 bits of data to a receiver identified by a 5 bit address The transmitted pulses are modulated at 40 kilohertz using either a 555 timer or 40 kHz crystal to generate the frequency 200 The Microcontroller Idea Book Wireless Links m n 3 GROUNDED CAS 5V QO X 2 T16 L co i Ga Alb oF Toe ur Io USAp2 4 DATA IN AF ASA 7 4HCOO MORI Ri pet GP1U52x RQ U4 55 ets IR RECEIVER 170K MC145Q27 C D6 5 A l F Q luF T ed sales REEDS X Ol Ro 7c2 E X pyLED4 z R ll REEDS X 330 VT VSS aS Zi ii ET Al A5 TO DESIRED ADDRESS EDS 1 4 INDICATE RECEIVED DATA ON OFF Sp 1 LEDS INDICATES VALID TRAN
224. ng to devices other than memory is often called input output or I O for short Adding Ports The 8052 BASIC has a few pins on Port 1 that you can use for I O Chapter 3 included programs for reading and writing to these But many projects will require more I O than these few pins can offer Figure 6 2 shows a circuit that allows you to add up to eight 8 bit ports to the main circuit You can design the ports as inputs or outputs in any combination The Microcontroller Idea Book 89 Chapter 6 DATA BUS D D7 U12 74LS244 2 8 iyi 1 BITO DI 6 D2 aa 4 HIGH ADDRESS BUS Ul 7 z 13 1A2 BIT 1 A8 A15 74HCT138 DA 91 1Y4 _ 2 1 1A3 BIT 2 DS 7 D6 522 8 EQQQH 1K D7 z1 2Y3 1A4 BIT 3 8 TTL E400 2Y4 i COMPAT I BLE E800 2A1 BIT 4 INPUTS ECQQH 3 FQQQH 2A2 BIT 5 5V g _ F400H E000H 1K 15 O F800H vgs 6e 2A3 BIT 6 6 FCQ0H 5 aie G1 READ 19 55 aaa Z ore j 74HCT32 GZA INPUT BUFFER EOOH 1678 ul4 74L8374 ADDRESS DECODER a gt 1D 10 L s BIT 4 D2 7122 5 a a3 20 gt gt BIT 4 D4 13 6 7150 3a F BIT 2 D6 1716P 9 5V D7 ape 40 BIT 3 8 TTL 8D i COMPAT I BLE POWER AND GROUND PINS Q 50 BIT 4 OUTPUTS IC 5V GND 15 60 gt BIT 5 ug 14 7 16 U11 16 8 Ate Siz 70 gt BIT 6 U12 20 10 O luF lyr 19 lul ly u13 14 7
225. ngs to Watch Out For This section is a summary of other bugs and other minor problems with BASIC 52 to be aware of as you program Many of BASIC 52 s bugs and limits have been eliminated in newer versions of BASIC 52 developed by other sources described in Chapter 15 Assembly language Issues In external code memory if 2002h contains 5Ah and bit 5 at 2048h is set BASIC 52 will try to call a user written token table If 2001h contains OAAh BASIC 52 will try to call a user written reset routine at 2090h If the expected table or routine isn t present the system will crash See Chapter 13 Solution avoid writing to code memory at 2001h 2002h and 2048h In Figure 3 1 s circuit the RAM in this area if any is accessed as data memory only so you don t have to worry about this The Microcontroller Idea Book 69 Chapter 5 The address following a CALL instruction must be at least 2000h Miscellaneous Items Floating point calculations have errors when the numbers are very large or very small The value returned for the ASC character operator is incorrect for these seven characters ONTIME and ONEX1 will not cause interrupts during an INPUT statement User delay in responding to an INPUT may cause the program to miss interrupts Finding Program Errors Writing a program that does what you want isn t always easy A single missing character or program line can cause a program to stop in its tracks or continu
226. nguage Later you can add non volatile memory for permanent program storage and interfaces to displays keypads and whatever else your projects require About the Circuit Figure 3 1 contains all of the components you need to get a BASIC 52 system up and running plus a few optional extras for future use Table 3 1 is a parts list for the circuit The circuit has five major components the 8052 BASIC chip U2 an address latch U4 an address decoder U6 static RAM U7 and an RS 232 interface U5 As Pll explain below a few of the components aren t essential at this point but ve included them to allow easy expansion later on The circuit configuration is a more or less standard design similar to many other microcon troller circuits When you understand this circuit you re well on your way to understanding many others The following paragraphs explain the circuit operation component by component If you re impatient to get started you can skim or skip over this section for now and go straight to the construction details The Microcontroller Idea Book 23 Chapter 3 5V DATA BUS 0 07 j u4 R2 R3 R4 RS R6 R7 RB RO 74HCT373 gorci5
227. nnected isn t transmitting while the decoder is receiving The program uses an edge detecting interrupt to ensure that the program won t re interrupt if VT is still low when the interrupt routine ends The main program is a do nothing loop that waits for an interrupt When VT goes high indicating that a valid transmission has been received the 8052 BASIC executes an interrupt routine that reads the data at bits 4 7 of Port B and displays it on the host computer Using VT to generate an interrupt is a handy way to detect when new data has arrived but you don t have to use interrupts If you don t enable interrupt 1 you can read Port 3 s bit 3 periodically to find out if a new transmission has arrived Or you can leave VT unconnected 210 The Microcontroller Idea Book Wireless Links 5V i 82 C 55 MC145027 ANY CMOS ee s INVERTER l D DATA iIn2 O 6 PB4 D6 Rl GPIUS2x Soe att R RECEIVER 24 6K PB6 Le D8 7 PB7 DO G a PCO Al eae ECL A2 f ae aca 8 13 5V Q 1uF 330K A5 TN VT REMOTE CONTROL DECODER INT ANY CMOS INVERTER Figure 12 7 Using an 8255 to control and access an infrared receiver and just read Port B once a minute or on user request or trigger the reading by some other factor under program control As with the encoder circuit you don t have to use an 8255 to read and write to the decoder A
228. nnel is paired with an adjacent one with the voltage on one channel referenced to the voltage on the other For example you could connect an output from a sensor to channel 2 and a ground or other reference from that sensor to channel 1 With differential mode selected channel 1 will read the difference between channel 1 s and channel 2 s voltage This mode cancels out errors due to noise that is common to both channels in the pair such as 60 cycle power line interference However because each channel uses two analog inputs this mode limits you to four channels The third mode of operation is pseudo differential In this mode channels 1 7 are all referenced to channel 8 This allows you to make 7 measurements all with the same reference This mode is useful if you are have multiple sensors in the same location Also if you connect channel 8 to a voltage greater than AGND the converter s range will shift to match with a 0 output occurring when an input equals channel 8 s voltage Reading the ADC To begin a conversion on the ADC0848 the 8052 BASIC writes to the converter indicating the desired channel and mode Bits 0 2 specify the channel O00 1 001 2 010 3 etc and bits 3 4 specify the mode of operation 00 differential 01 single ended 11 pseudo differential So for example in Figure 9 4 s circuit to begin a single ended conversion at channel 5 you would write 0000 1101 or ODh to the converter s address The Mi
229. noise by switching power only when the AC signal is near zero volts The Microcontroller Idea Book 185 Chapter 11 SOLID STATE RELAY NORMALLY OPEN CONTROL AC LOAD ENG Ny 5V O 117VAC O DATA BUS DO D7 74LS374 5 AC LOAD ID 10 2D 202 3D so 4D Ao EACH BIT MAY CONTROL A 5D 5qu2 SOLID STATE RELAY 6D 60H 2 7D 7o 5 8D gor E400H l LlfoLk SOLID STATE RELAY WRITE lige NORMALLY OPEN 74HCTO2 LATCH CONTROL DC LOAD 5V DC LOAD Figure 11 1 Solid state relays provide an easy way to switch power to AC or DC loads Using a solid state relay saves you the trouble of building a similar circuit from discrete components Surplus relays are inexpensive as low as 1 50 each from vendors such as All Electronics Marlin Jones and Hosfelt If you don t have a data sheet for your relay look for a pair of control pins usually labeled and The other two pins connect to the load In Figure 11 1 the control bits are outputs of a 74LS374 latch addressed at E400h as described in Chapter 6 On a normally open relay the load switches on when its control bit is low If you want a logic high to turn on the load wire an inverter between the 374 s output and the relay or use a normally closed relay Or you can use a 74HCT374 latch in place of 186 The Microcontroller Idea Book Control Circuits the LSTTL p
230. nonvolatile RAM are available for any use The chip is shown addressed at AOOOh but you can use any unused chip enable The chip s WE and OE inputs are driven by RDANY and WRITE The DS1286 has two interrupt outputs INTA and INTB You can program one of these to toggle or pulse whenever the time and or day match stored values The other can generate an interrupt if the DS1286 s watchdog register isn t accessed periodically You can use this feature to automatically reset a system if a program crash causes the program to stop The Microcontroller Idea Book 175 Chapter 10 DATA BUS DO D7 LOW ADDR AO A7 ESS BUS DS1286 DQO DQ DQ2 DQS DQ4 DQ5 DQ6 DQ7 AOQOOH WRITE RDANY CE WE O QE VCC H INTA cnp LL4 INTB SQW NO JN NINIS wO NINIS WATCHDOG TIMEKEEPER Figure 10 2 Wiring diagram for the DS1286 Watchdog Timekeeper in an 8052 BASIC system accessing the watchdog register When IPSW register B bit 6 is 1 the time of day interrupt is on INTA and the watchdog interrupt is on INTB When IPSW is 0 these are reversed with the watchog on INTA and the time of day on INTB The chip also has a 1024 Hz square wave output Table 10 1 details the functions of the DS1286 s registers which store time date configu ration and status information To initialize the clock calendar you write the current time and date into registers 0 2 4 6 and 8 thr
231. ns 47 Adding NVRAM or EEPROM 50 Using the Programming Commands 53 Adding Bootup Options 54 11 23 47 Erasing NV Memory 55 Adding more NVRAM or EEPROM 56 Adding EPROM 56 EPROM programming Circuits 57 Power Supplies for Programming 61 Storing Programs on Disk 63 Chapter5 Programming 65 Programming Basics 65 BASIC 52 Bugs and Things to Watch Out For 69 Finding Program Errors 70 BASIC 52 Keywords by Function 72 Quick Reference to BASIC 52 74 Chapter 6 Inputs and Outputs 87 The Memory Map 87 Uses for I O Ports 89 Adding Ports 89 The 8255 Programmable Peripheral Interface 98 Chapter 7 Switches and Keypads 109 Simple Switches 109 Adding a Keypad 116 Chapter 8 Displays 125 Using LEDs 125 7 segment Displays 129 Displaying Messages 138 Inside the Display Controller 140 Mounting Displays in an Enclosure 152 Chapter9 Using Sensors to Detect and Measure 153 Sensor Basics 153 Choosing Sensors 154 On off Sensors 155 Analog Sensors 156 Sensor Examples 163 Level Translating 167 Choosing a Converter 169 Chapter 10 Clocks and Calendars 171 BASIC 52 s Real time Clock 171 A Watchdog Timekeeper 174 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Appendix A Control Circuits Switching Power toa Load 185 Controlling a Switch Matrix 187 Op Amp with Programmable Gain 189 Controlling a Stepper Motor 191 Speed Control of a Continuous DC Motor 195 Wireless Links Infrared Links 199 Increasing the
232. ns connected to pins and 2 of the 8052 BASIC as in Figure 7 4 This program stops reading the switch as soon as it detects a switch press so debouncing 114 The Microcontroller Idea Book Switches and Keypads 8052 BASIC NORMALLY cas OPEN PUSHBUTTON 2 NORMALLY P1 1 OPEN PUSHBUTTON Figure 7 4 Two pushbuttons connected to port pins on the 8052 BASIC isn t required When you use polling you have to be sure to check the switch often enough so that you won t miss a switch press For example if you read the switch once per second and you press the switch for just 100 milliseconds you may not detect the switch press Latching a Switch Press Another solution to switch detecting is to latch the switch press as Figure 7 5 shows In this circuit a switch press causes the Q output of a 74HC74 flip flop to go low and remain low until an external signal clears the flip flop The circuit uses two port bits one input P1 0 and one output P1 1 Both should be set high to begin The flip flop s Q output connects to P1 0 which the program can read at its leisure If the bit is low someone has pressed the switch To reset the bit the program brings P1 1 low then high to clear the flip flop and bring Q high again ready to detect another switch press You can use any free port bits in place of P1 0 and P1 1 Listing 7 2 Monitors two switches and displays a message when one is pressed
233. nts extra interrupts due to switch bounce Figure 7 3 shows a hardware debouncing circuit that uses a 74HC14 inverter with Schmitt trigger input The circuit generates a clean pulse when S1 is pressed in spite of switch bounce that may occur Point B the inverter s input is normally low and point C the inverter s output is normally high When S1 is pressed C1 discharges slowly through R2 and the switch contacts If switch bounce occurs the voltage at the inverter s input can t change rapidly enough to affect the logic state of the input Only when the switch remains closed for around 50 milliseconds does point B go high enough to cause point C to switch low In a similar way when the switch contacts open C1 charges slowly though R1 and R2 and pin C goes high again only when the contacts have remained closed for around 50 milliseconds The Schmitt trigger input ensures that the output pulse is clean even if the input changes slowly As with software debouncing you can experiment to find the minimum values that prevent unwanted interrupts due to switch bounce The debounce time increases as you increase the values of C1 and R2 Level detecting interrupts If you use a level detecting interrupt instead of an edge detecting one the interrupt routine executes whenever there is a low logic level at pin 13 So for example if you press and hold the switch in the above example the interrupt routine will execute again and again un
234. ny combination 188 The Microcontroller Idea Book Control Circuits Listing 11 1 Controls an MT8808 switch matrix 10 REM A base address of 82C55 20 A 0FC0O0H 30 REM configure 8255 for all outputs 40 XBY A 3 80H 50 REM bring MT8808 s Reset low off 60 XBY A 3 OEH 70 XBY A 0 80 DO 90 INPUT Open 0 close 1 or reset all 2 2Z 100 IF Z 2 THEN GOSUB 300 110 IF Z THEN GOSUB 400 120 WHILE 1 1 130 END 290 REM reset all switches by toggling Reset 300 XBY A 3 0FH 310 XBY A 3 0EH 320 RETURN 400 PRINT Enter inputs to connect or open 410 INPUT X 0 7 X 420 INPUT Y 0 7 Y 430 REM write to MT8808 to open or close selected switch 440 B X Y 8 2 40H 450 XBY A B 460 XBY A B 80H 470 XBY A B 480 RETURN Listing 11 1 demonstrates switch operation by asking you whether to open or close a switch or reset them all then performing the requested action Op Amp with Programmable Gain Figure 11 3 shows a way to set the gain of an operational amplifier by writing to three output port bits Controlling the gain is National Semiconductor s LF13006 or LF13007 digital gain set IC Each contains a resistor ladder switches and decoding logic that enable you to select any of eight gains for an amplifier attenuator current source or other circuit that requires precise variable outputs Each of the gain set ICs has two outputs each with a different series of gains as
235. ny latched port outputs will do for A1 A4 and any port inputs will do for D6 D9 Because the decoder latches the data you don t need additional input latches If the circuit will receive data from only one address you can hardwire the decoder s A1 A5 and free up four bits on the 8255 for other uses You can transmit to Figure 12 7 s circuit with either a manual or computer controlled transmitter Set the transmitter s address inputs to match the receiver s address select the data you want to send transmit and view the received data on the 8052 BASIC system s host display The Microcontroller Idea Book 211 Chapter 12 Listing 12 2 Reads received data at the decoder 10 REM 8255 mode set Ports A C output Port B input 20 XBY OFCO3H 82H 30 REM A decoder address 0 15 40 A 2 50 REM Write address to Port C turn TE PC 7 off high 60 XBY OFCO2H 80H A OR XBY OFCO2H 70 REM Use edge triggered interrupt 80 TCON TCON OR 4 90 DO 100 REM Wait for interrupt 110 ONEX1 500 120 WHILE 1 1 130 END 480 REM On interrupt 1 print received data 490 REM Data is at Port B bits 4 7 500 PHO XBY OFCO1H AND OFOH 10H 510 RETI You can have more than one receiver in a link If each has a unique address it will accept only the transmissions meant for it Increasing the Distance When you have your link up and running one of the first challenges is to see how far you can reliably transmit Two ways to i
236. ny situation that requires flexible changeable routing of analog or digital signals A Mitel MT8808 8 x 8 analog switch array simplifies the circuit design and programming The chip contains an array of crosspoint switches plus a decoder that translates a 6 bit address into a switch selection and latches that control the opening and closing of the switches Maxim is another source for switch arrays like this Connecting an X and Y input requires the following steps Write the X and Y addresses to AX0 AX2 and AY0 AY2 Bring STB high Bring DATA high to close the switch Bring STB low to latch the data To open a connection between an X and Y input you do the same but bring DATA low to open the switch You can make and break as many connections as you want by writing the appropriate values to the chip All previous switch settings remain until you change them by writing to the specific switch You can connect the switches in any combination For example you can connect one X input to each of the eight Y inputs to create eight distinct signal paths Or you can connect all eight Y inputs to a single X input to route one signal along eight different paths The Microcontroller Idea Book 187 Chapter 11 The MT8808 is shown powered at 5V but VDD may be anywhere from 4 5V to 13 2V VEE is an optional negative supply that enables you to switch negative signals The switches do have some resistance which varies with the supply voltage At
237. nz 20h nextvalue do another if count gt 0 jb ri return after writing one complete cycle check serial receive flag and quit if set sjmp nextcycle if serial flag not set begin another cycle Return to BASIC 52 return clr FI clear serial receive flag ret return to BASIC end The Microcontroller Idea Book 229 Chapter 13 FOR loop by loading FFh into register dpl the lower byte of dptr and decrementing dpl repeatedly until it equals zero In assembly language you also do not have built in conveniences like BASIC 52 s ability to terminate a program on CONTROL C You have to add these features yourself In Listing 13 5 after each complete cycle of the sine wave the program checks the serial port s receive flag If the flag is set it means that the user has pressed a key and the program returns to the BASIC 52 prompt Otherwise the program begins another cycle of the sine wave To run Listing 13 5 create a source file with your text editor assemble it and upload it to RAM as before Edit Listing 13 4 by removing lines 150 180 and adding this line 150 CALL 3100h Now when you run Listing 13 4 you should again see a sine wave at VOUT but at a much higher frequency With a 12 Megahertz crystal the sine wave should be around 350 Hertz or 2 8 milliseconds per cycle You can verify this by consulting the 8052 s data book which tells the number of machine cycles required to execute each instruction At 12 Mega
238. o run as long as it remains connected to the port and you don t write anything else to it Speed Control of a Continuous DC Motor If you prefer ordinary continuous dc motors to steppers Figure 11 5 shows a circuit that uses BASIC 52 s PWM output to control motor speed This circuit uses another Allegro chip the UDN2993B U1 Pins 1 and 8 of U1 connect to the motor s power supply which can range from 10 to 40V Pins 6 and 7 connect to the motor Pin 5 is the 5V logic supply and pins 4 5 12 and 13 are additional grounds At pins 10 11 14 and 15 you can connect and control a second motor Pin 3 of U1 controls motor direction and connects to bit O of Port 1 P1 0 on the 8052 BASIC Pin 2 of U1 switches power to the motor with a logic low shutting the motor off and a logic high allowing current to flow This pin connects to Portl bit 2 P1 2 of the 8052 BASIC which is the PWM output BASIC 52 s PWM expression causes a series of pulses to appear at P1 2 with this syntax The Microcontroller Idea Book 195 Chapter 11 PWM high pulse width low pulse width number of cycles Listing 11 4 uses the PWM output to control motor speed The program prompts you for motor direction and the width of the high and low PWM pulses For faster speeds use large values for the high pulses H and small values for the low pulses L This results in a waveform with a high duty cycle or ratio of the width of a high pulse to the width of
239. o ways to read the state of a normally open switch sensor A basic input B latched input Listing 9 1 assumes that in Figure 9 1B the Q output connects to bit O of an input port at E000h and the CLR input connects to bit 0 of an output port at E400h The program clears the flip flop then reads the input port continuously until the bit in question goes high It then displays a message clears the flip flop and returns to the main program Analog Sensors The above sensors have just two states on and off or open and closed This makes them easy to use in digital circuits which recognize only two logic states 156 The Microcontroller Idea Book Using Sensors to Detect and Measure Listing 9 1 Reads and clears a flip flop output connected to an input port pin 10 REM clear flip flop 20 XBY 0E400H 0 30 XBY 0E400H 1 40 DO 50 REM read port 60 A XBY 0E000H 70 REM see if bit 0 is set 80 IF A AND 1 1 THEN GOSUB 200 90 WHILE 1 1 100 END 200 PRINT vibration alarm 210 REM clear flip flop 220 XBY 0E400H 0 230 XBY 0E400H 1 240 RETI Many sensors have analog outputs however They vary continuously in response to changes in the properties they sense For example the resistance of a Cadmium sulfide CdS photocell varies with the intensity of light hitting it If you want to use an analog sensor like this in an 8052 BASIC system you need to add some components to convert the analog signal to digital A c
240. ode display to find the common cathode pin or pins connect a pin to 5V and touch the others to ground through the 330 ohm resistor The pin or pins that cause the segment to light are the common cathode connections To find the pin that controls each segment move the 5V lead to each pin in turn and note the results Interfacing For 7 segment decoder drivers you can choose from single digit and multi digit chips Single digit driver Figure 8 4 shows a 7 segment display controlled by a 4511B latch de coder driver The display shows the value of the 4 bit number at the 4511 s data inputs A D The 4511 will drive common cathode displays directly Common anode displays require inverters at the segment outputs You can use any output port bits to control the display An 8 bit port will control a 2 digit display Listing 8 2 tests Figure 8 4 s circuits by displaying each digit in sequence The program assumes that a display connects to bits 0 3 of Port Aon an 8255 addressed at FCOOh If your system has different addressing change the program to match Multi digit driver If you want to display more than a couple of digits there are specialized chips that will drive and control multiple digit displays One example from Intersil now part of Harris Semiconductor is the ICM7218D multiplexed display driver which can control up to 8 common cathode digits Figure 8 5 illustrates For common anode displays use the ICM7218C The segments of al
241. omparator provides a way to detect a specific analog voltage Figure 9 3 shows how to use a comparator to detect a specific light level on a photocell A comparator is a special form of op amp with analog inputs but a digital output In Figure 9 3 pin 4 is a reference voltage and pin 5 is the input being sensed When the sensed input is lower than the reference the comparator s output is low When the sensed input is higher than the reference the comparator s output is high R1 and the photocell form a voltage divider As the light intensity hitting the photocell increases its resistance decreases and pin 5 s voltage rises To detect a specific light level adjust R2 so that VOUT switches from low to high when the light reaches the desired intensity You can read the logic state of VOUT at any input port pin R4 is a pull up resistor for the LM339 s open collector output R3 adds a small amount of hysteresis which keeps the output from oscillating when the input is near the switching voltage The Microcontroller Idea Book 157 Chapter 9 CADMIUM am SULFIDE PHOTOCELL VOUT DARK 1 LIGHT 1 4 LM339 COMPARATOR ADJUST R2 SO VOUT SWITCHES AT DEST RED LIGHT LEVEL Figure 9 3 The comparator s output switches at the light level determined You can use the same basic circuit with other sensors that vary in resistance Replace the photocell with your sensor and adjust R2 for the switching level you w
242. omponents in your projects For a small charge many component vendors will send along data sheets for the parts you order Host Computer To program the 8052 BASIC you connect its circuits to a host computer using an RS 232 asynchronous serial port and terminal emulation software The computer can be any type as long as it has a serial port and appropriate software The serial port is the same connector where you plug in an external modem serial printer serial mouse or other RS 232 serial device Terminal emulation software is the same type of software that you may use for modem communications with an on line BBS Examples for MS DOS computers are Datastorm Table 2 1 Differences among 8051 family chips Chip Program Memory Ram Timers bytes Type kilobytes 8051 ROM 4 128 2 8052 ROM 8 256 3 8031 none 128 8032 none 256 3 8751 EPROM 4 128 2 8752 EPROM 8 256 3 e 80051 80C52 80C31 and so on are CMOS versions of above e 80C51FA B C add more versatile timers and an enhanced serial channel e 8052 BASIC has the BASIC 52 programming language in ROM e Packages include 40 pin DIP 40 lead PLCC and 44 pin QFP Tne Microcontroller Idea Book 15 Chapter 2 Technologies Procomm Plus and the Terminal accessory in Microsoft Windows At mini mum the software must enable you to do the following set the baud rate and other communications parameters serially transmit the characters that you type at the keyboard
243. on C 60 IF C 0 THEN L L AND OFFH 2 B 70 IF C 1 THEN L L OR 2 B 90 XBY A L 80 WHILE 1 1 90 END outputs of a 74LS374 addressed at E000h The LEDs are connected as in Figure 8 1B with logic low outputs turning on the LEDs Listing 8 1 tests the circuit by allowing you to turn individual LEDs on and off Bi color LEDs Bi color LEDs have both a red and a green LED inside a single package By turning on one both or neither you can use a single indicator to show as many as four states Some bicolor LEDs have two leads while others have three Figure 8 2 illustrates In the 3 lead or common cathode type the cathodes of both LEDs connect internally A To turn on an LED you ground the cathodes through a current limiting resistor and apply power to the anode of the desired LED When both LEDs are powered you get an amber light Removing power from both turns the LED off giving a total of four states that the device can display Instead of the one current limiting resistor shown you can connect a resistor to each anode to set the current through each LED individually In a 2 lead or parallel connected bicolor LED the anode of each LED connects internally to the other s cathode B To turn on the red LED you apply 5V to terminal A and ground terminal B To turn on the green LED you do the reverse terminal A is ground and terminal B is 5V With this type you can t turn on both LEDs at once With either ty
244. on t have to string wires from point to point On an 8052 BASIC system you can use a wireless link to send commands to devices that recognize and act on them Or in the other direction the devices might transmit to an 8052 BASIC system that acts on the information received Or you can have two 8052 BA SIC systems that communicate with each other over the wireless link This chapter describes ways to do these using infrared energy or radio waves as the transmitting medium Infrared Links Over short distances and at lower speeds infrared is a good choice for wireless links Figures 12 1 and 12 2 show a link whose transmitter sends 4 bit messages to one or more receivers Each receiver has a 5 bit address which enables the transmitter to send a message to a selected receiver while other receivers will ignore it These circuits are independent modules controlled by manual switches or jumpers rather than by a microcontroller This is a good way to get the link up and running When that s The Microcontroller Idea Book 199 Chapter 12 S1 TRANSMIT 3V yT ENABLE o ige l aS io F plavo TE P R3 ae e e DATA OUT QI S AEE MPS2907 te UI 74HCT132 te Haga MC145026 Ho 5 Rl R4 re SAS 4QKHZ IN 75 Ho 6 13 43K fa D6 RTC T pa D7 12 7 1uF n rr 28 CTC ae fi
245. ontain instructions that are valid but that do not do what you intended It s a good idea to at least scan the listing created by the assembler before you try to run a routine to look for obvious errors Different assemblers may have slightly different syntax rules For example some require org and end to have a leading period org end Check your assembler s documentation for the specifics Uploading a Program When you re ready to load the program into RAM boot your 8052 BASIC system connect the serial link to your personal computer and run your communications software Use the software to upload Listing B 1 or B 2 in the same way that you upload any BASIC 52 program from disk For loading Intel hex files you can set up your host computer s software so that it waits to receive the BASIC 52 gt prompt ASCII code 62 after each uploaded line This will ensure that BASIC 52 has enough time to process each line before the next one arrives Use this method only with Intel Hex files not BASIC 52 programs If a BASIC 52 program contains any gt greater than operators the software will think that these indicate the end of a program line Intel Hex files contain no gt characters so there is no problem If you want to wait for the gt character in Procomm Plus from the Setup menu select Terminal Options then Protocol Options ASCII Options and set the pace character to 62 Character pacing and l
246. ontroller Idea Book Calling Assembly language Routines Avoiding Program Crashes It s very easy to write an assembly language program that crashes the system and forces you to reboot To prevent this you have to take care that your routines do not interfere with each other or with BASIC 52 Remember that BASIC 52 is a program in itself and it uses many of the registers and other memory locations both inside and outside of the 8052 for its own purposes For example BASIC 52 uses locations 13h and 14h in internal RAM to store the starting address of the current BASIC program in external RAM If you overwrite these values BASIC 52 will no longer be able to find your program The BASIC 52 programming manuals list the registers and other memory addresses used by BASIC In general you should avoid writing to these locations unless you know what you re doing and how to deal with the results Often an assembly language routine will alter some of the 8052 s registers You are responsible for seeing that all critical values are unchanged when the routine returns control to the program that called it whether it s BASIC 52 or another assembly language program The stack is a convenient way to preserve values on entering a routine and to restore them on exiting The stack is a special area of memory with a last in first out structure which means that you read values from the stack in the reverse order that you wrote them Storing values
247. operating system to handle multiple tasks Examples include solenoid cyclers a pulse generator envelope detector and motor speed control using the C programming language The 8051 Family of Microcontrollers by Richard H Barnett Prentice Hall 1995 164 pages 49 The 8051 Microcontroller 2nd edition I Scott MacKenzie Macmillan 1994 356 pages 58 Includes schematics for a single board computer assembly language source code for a monitor program and interfaces to a keypad LEDs and loudspeaker The 8051 Microcontroller Architecture Programming and Applications Kenneth J Ayala West Publishing Company 1991 241 pages 49 Includes disk with assembler and simulator The 8051 Microcontroller Hardware Software and Interfacing James W Stewart Regents Prentice Hall 1993 27 50 273 pages Includes many interfacing examples such as switches solenoids relays shaft encoders displays motors and A D converters and a chapter on top down design method 252 The Microcontroller Idea Book Sources Programming and Interfacing the 8051 Microcontroller by Sencer Yeralan and Ashutosh Ahluwalia Addison Wesley 1995 40 328 pages Programming and Interfacing with Microcontrollers Experimenting with the 8031 Fam ily of Microcontrollers Rigel Corporation Data Books Data books are where to look for specific detailed information about a particular IC They re also a good source for application examples Na
248. or many control monitoring and other tasks BASIC 52 is fine For example a weather station that senses conditions once per minute and stores or displays the results doesn t need super fast response And if necessary you can call an assembly language routine for a portion of a program where speed is critical Even if you write your programs in assembly language C or another language you can use the 8052 BASIC system as a development system that enables you to upload your program to memory run the program and test and debug your programs and circuits e Another limitation of the 8052 BASIC is that a complete project requires additional components If you re looking for a true single chip solution the 8052 BASIC isn t it Even a minimal system requires an external RAM chip and most systems also have an external EPROM or other non volatile memory The serial link and other optional functions also use some of the on chip timers and input output ports so these may not be available for other uses Still the 8052 BASIC lets you to do a lot with a little When needed you can easily add chips to expand the input output ports timers and other functions e And finally don t expect BASIC 52 to have the abilities of QBasic Visual Basic or other BASIC programming languages that you may use on your personal computer BASIC 52 is more capable than many other single chip BASICs It includes features like loops subroutines string handling
249. order suppliers An output capability of at least 500 milliamperes is recommended Capacitors C8 C13 provide power supply decoupling Digital devices draw current as they switch Capacitors C9 C13 store energy that the components can draw quickly without causing spikes in the supply or ground lines C8 stores energy for quick recharging of C9 C13 The exact values aren t critical but C9 C13 should be a type with good high fre quency response such as ceramic mica or polystyrene LED1 and current limiting resistor R10 are an optional power on indicator 30 The Microcontroller Idea Book Powering Up Figure 3 3 This is the circuit board on which wire wrapped and tested many of the circuits in this book Circuit Construction This circuit is intended for use as a flexible system for testing and experimenting rather than a fixed unchanging design for a single application For this reason I recommend building it with wire wrapping or another construction method that allows easy changes and additions Figure 3 3 shows an 8052 BASIC circuit wire wrapped onto perfboard Reading the Schematic In the schematic I used a couple of different techniques to represent connections between pins and components In the reset circuit connections are drawn as direct point to point lines For the address and data lines I used buses for a neater more compact schematic When you wire these connections use the signal labels as a guide For ex
250. ore number of bytes to program B E S 1 GOSUB 500 DBY 1FH BH DBY 1EH BL REM store starting address of destination 1 B P 1 GOSUB 500 DBY 1AH BH DBY 18H BL PHO eprom low BL PHO eprom high BH The Microcontroller Idea Book Calling Assembly language Routines Listing 13 8 page 2 of 2 310 REM store starting address of source 320 B S GOSUB 500 DBY 1BH BH DBY 19H BL 330 PHO ram low BL 340 PHO ram high BH 350 PRINT press ENTER to begin programming 360 X GET IF X lt gt 0DH THEN 360 370 REM program the EPROM 380 PRINT programming in progress 390 PGM 400 REM check for errors 410 IF DBY 1EH OR DBY 1FH 0 THEN PRINT programming OK GOTO 470 420 REM on error calculate address that failed to program 430 DC DBY 19H 256 DBY 1BH 1 440 PHO ERROR Source address DC XBY DC 450 DP DBY 18H 256 DBY 1AH 460 PHO Destination address DP XBY DP 470 END 500 REM separate B into high BH and low BL bytes 510 BL B AND OFFH 520 BH INT B 256 530 RETURN A General purpose EPROM Programmer With Listing B 2 you can use an 8052 BASIC system as a general purpose programmer for EPROM EEPROM or NV RAM The program will read any file in Intel Hex format and store it at the addresses specified in the file For example you can add a socket for an 8K EPROM EEPROM or NV RAM addressed at AOOOh BFFFh in
251. ort A use PRINT XBY OFCOOH or PHO XBY OFCOOH To read Port B or C use the same statement but with OFCO1H or OFCO2H to select the port you desire To configure all all bits as outputs in mode 0 use this statement XBY OFCO3h 80H Then to write a value to Port A use XBY OFCOOh xx where xx is the value to be written Use FCO1h to write to Port B and FCO2h for Port C Combinations of Inputs and Outputs Fourteen other combinations of inputs and outputs are possible by setting or clearing bits 0 1 3 and 4 in the control word as shown in Figure 6 7 To change the mode settings determine which bits to set and clear for the configuration you want convert the value to decimal or hexadecimal and write the value to OFCO3h One handy feature of the 8255 is that you can read back the last value written to an output port With the ports configured as outputs you can use the same statements you use to read the input ports At Port B or C reading an output port gives the value in the output latch which contains the last value you wrote to the port Port A works a little differently Instead of reading the output latch you read the actual logic states on Port A s pins This means that at Port A if a bit is shorted to ground you will read back a O for that bit even if the last value written to it was a 1 The Microcontroller Idea Book 105 Chapter 6 CONTROL WORD D7 06 D5 D4 D3 D2 DI DO YU
252. ou might think This is because the 8052 does not execute the BASIC programs directly Instead the BASIC 52 interpreter program reads the BASIC programs as data and then translates them to machine code for execution by the 8052 If you don t need all of the available memory space you can combine code and data memory in a single area With combined memory WR controls write operations and PSEN and RD are logically ANDed to create a read signal that is active when either PSEN or RD is low Combined data code memory is handy if you want the flexibility to store either BASIC or assembly language programs in the same chip or if you want to be able to upload assembly language routines into RAM for testing ALE is the final control signal for accessing external memory It controls an external latch that stores the lower address byte during memory accesses When the 8052 reads or writes to external memory it places the lower address byte on ADO AD7 and strobes ALE which causes the external latch to save the lower address byte for the rest of the read or write cycle After a short delay the 8052 replaces the address on ADO AD7 with the data to be written or read Timers and Counters The 8052 has three 16 bit timer counters which make it easy to generate periodic signals or count signal transitions BASIC 52 assigns optional functions for each of the timer counters Timer 0 controls a real time clock that increments every 5 milliseconds You can us
253. ou write it without a separate compile or assembly step A compiler is a good choice when a program is long or has to execute quickly A single language like BASIC may be available in both interpreted and compiled versions Each device family requires its own interpreter or compiler to translate the higher level code into the machine code for that device In other words you can t use QuickBASIC for IBM PCs to program an 8052 microcontroller you need a compiler that generates program code for the 8052 Compared to an equivalent program written in assembly language a compiled program usually is larger and slower so assembly language is the way to go if a program must be as fast or as small as possible A higher level language also may not offer all of the abilities of assembly code though you can get around this by calling subroutines in assembly language when necessary BASIC 52 is an interpreted language but BASIC compilers for the 8052 are also available In fact you can have the best of both worlds by testing your programs with the BASIC 52 interpreter and compiling the finished product for faster execution and other benefits of the compiled version Testing and Debugging After you ve written a program or a section of one it s time to test it and as necessary find and correct mistakes to get it working properly The process of ferreting out and correcting mistakes is called debugging Easy debugging and troubleshooting can m
254. ough A then start the clock by clearing EOSC bit 7 of register 9 Time and date values are stored in binary coded decimal BCD format In BCD a 4 bit nibble represents one decade and nibbles greater than 9 1001 are not allowed Table 10 2 shows numbers expressed in decimal BCD and binary Some values in the DS1286 don t require a full 8 bits For example since the month can go no higher than 12 you need only 5 bits to store its value 176 The Microcontroller Idea Book Clocks and Calendars Table 10 1 Register functions for the DS1286 Watchdog Timekeeper Register Function Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 0 Clock 0 1 seconds 0 01 seconds 1 0 10 seconds seconds 2 0 10 minutes minutes 3 Alarm MASK 10 minutes alarm minutes alarm 4 Clock 0 12 24 10hror 10hr hours AM PM 5 Alarm MASK 12 24 10hr or 10hr hour alarm AM PM 6 Calendar 0 0 0 0 days 7 Alarm MASK 0 0 0 day alarm 8 Calendar 0 0 10 date date 9 Oscillator EOSC ESQW o 10mo months A 10 years years B Command TE IPSW JIBH LO PU LVL WAM TDM WAF TDF C Watchdog 0 1 seconds 0 01 seconds D 10 seconds seconds E 3F User free for any use Time of Day Alarm Mask Bits Minutes Hours Day Alarm Frequency 1 1 1 Once per minute 0 1 1 When minutes match 0 0 1 When hours and minutes match 0 0 0 When hours minutes and
255. output appears at VREF This configuration is the inverse of the device s current switching mode where VREF is an input and IOUT1 and IOUT2 are outputs as their names suggest Op amp U2A buffers the output and U2B is a low pass filter that helps to smooth VOUT A BASIC Program Listing 13 4 causes a sine wave to appear at VOUT The sine wave represents the value of the trigonometric sine function for an angle that varies continuously from 0 to 360 degrees or 0 to 6 28 2 PI radians Lines 90 110 are a loop that selects 256 equally spaced points along one cycle of the sine wave calculates the sine for each and stores the values in RAM The program uses BASIC 52 s SIN operator in calculating the values Sine values normally vary from 1 to 1 but line 100 adjusts the values so that they vary from 0 to 255 which is the range of inputs accepted by the 8 bit DAC Using these values 0 is the negative peak 255 is the positive peak and the zero crossing occurs midway between points 127 and 128 To generate the sine wave Lines 150 180 are a loop that reads each value in sequence from RAM and writes it to an output port at E400h After writing a complete cycle the program loops back and begins another The sine wave repeats endlessly until the user presses CONTROL C Listing 13 4 creates a perfectly good sine wave but at a very low frequency Using 12 Megahertz crystal to clock the 8052 the frequency is only about 0 7 Hertz or 1 5 secon
256. own enable input 1G and 2G For this application the enables are tied together and all eight buffers are accessed as a group I used an LSTTL device for the buffer rather than a CMOS 74HC244 for a couple of reasons The LSTTL chip has Schmitt trigger inputs which are less sensitive to noise Plus unlike CMOS the LSTTL buffer requires no pull up resistors at unused inputs OR gate U9B ensures that U12 is enabled only when U2 the 8052 BASIC chip reads an address from E000h to E3FFh When this occurs output enable pins 1 and 19 go low the buffer s outputs follow its inputs and U2 reads the data that U12 has placed on DO D7 After a read operation pins 1 and 19 go high and U12 s outputs are high impedance In other words the outputs are electrically similar to an open circuit which ensures that they won t interfere with other operations on the data bus In the circuit U12 is read only Write operations to EO00h have no effect To access U12 at a different address wire pin 4 of U9B to a different output of U11 Memory decoding options Note that although U12 holds just one byte of information to read you can access it at any address from EO00h to E3FFh This may seem like a waste of The Microcontroller Idea Book 91 Chapter 6 1023 3FEh addresses Indeed if using every byte of memory is critical you can use other methods in place of U11 to more completely decode or divide the memory space Programmable logic is one
257. pe by adding an inverter you can use a single output to control both LEDs C D 128 The Microcontroller Idea Book Displays ha A B OFF O Oo OFF 2 EREN Bo Green lo BED o RED 1 AMBER 11 OFF 1 1l A COMMON CATHODE TYPE 2 LINE CONTROL B PARALLEL CONNECT TYPE 2 LINE CONTROL 1 RED 1 RED gt e a Q GREEN gt GREEN ANY ANY HCMOS HCMOS INVERTER INVERTER 220 220 C COMMON CATHODE TYPE I LINE CONTROL D PARALLEL CONNECT TYPE 1 LINE CONTROL Figure 8 2 Ways to connect bicolor LEDs 7 segment Displays If you want to display numbers 7 segment displays will do the job Each digit on the display contains seven segments Numerals are displayed by turning on different combinations of segments as Figure 8 3 shows Decoder chips make it easy to operate one or more displays with a minimum of programming and added components Seven segment displays are available as LEDs where each segment is a light emitting diode and as LCDs where each segment is a liquid crystal display We Il look at the LED type first 7 segment LEDs A 7 segment LED contains seven individual LEDs arranged in the pattern shown in Figure 8 3 Sometimes there is also a decimal point or two one on each side There are also special leading digit modules that display only a 1 and a plus or minus symbol The Microcontroller Idea Book 129 Chapter 8
258. ple 1Fh If the first character is in the range A F you must also add a leading 0 Example OE9h BASIC 52 s PHO and PH1 operators display numbers in hex format on the host computer s screen 2 2 The Microcontroller Idea Book Number Systems This table shows the value of each character in C h which is the hexadecimal representation of the decimal number 193 Hex character C 1 Character multiplier 16 160 Character value decimal 192 1 Binary coded Decimal Numbers Binary coded decimal or BCD is yet another way of expressing numbers It allows easy translation of binary bits to decimal values Chapter 10 has more on this number system Kilobytes and Megabytes Two other popular terms for dealing with quantities in the computer world are kilobyte and Megabyte In the metric system of measurement kilo means 1000 but in the computer world it commonly refers to 1024 Ome or 400h in hexadecimal So an 8 kilobyte RAM chip actually stores 8192 bytes not 8000 K is short for kilobyte 8K equals 8 kilobytes In an similar way in the metric system Mega means a million but in the computer world it commonly refers to 1 048 576 Ons or 1000h in hexadecimal One Megabyte equals 1024 kilobytes M is short for Megabyte 8M equals 8 Megabytes The Microcontroller Idea Book 273 274 The Microcontroller Idea Book Index A ADC 158 169 address bus 27 28 address latch disable 22 address latch enable
259. ple you could add an 8K NVRAM addressed from 2000h to 3FFFh or a 16K EPROM from 4000h to 7FFFh Software for Uploading You ll also need a way to load your routines from your personal computer into your 8052 BASIC system s memory All that s required here are your host computer s commu nications software and a BASIC 52 program that reads and stores the uploaded file Appendix B contains two such programs Listing B 1 HEX2RAM BAS loads Intel Hex files from your personal computer into RAM including NVRAM in a BASIC 52 system Listing B 2 HEXLOAD BAS does the same and also offers the options of loading into EPROM or EEPROM On your host computer you can the same communications software that you use to upload BASIC 52 programs as described in Chapter 3 Another option for loading routines from your host computer into memory is to program an EPROM or other device with a device programmer and then insert the programmed device into your BASIC 52 system If you use this method you can access the chip as code only memory rather than combined code data memory since you don t need to write to it when it s installed in the 8052 BASIC system Loading a Routine When you have the necessary tools you re ready to write an assembly language routine and assemble upload and call or run it As a first try we ll begin with a very simple routine just to verify that the circuits and techniques are working Listing 13 1 has j
260. r s keyboard and screen make it easy to write and run programs and view the results BASIC 52 has many built in debugging features that make it easy to test programs You can run a program immediately after writing it without having to assemble compile or program an EPROM You can use a STOP statement and CONT continue command to set breakpoints and resume executing your program You can use PRINT statements to display variables as the program runs And if you wish you can use your personal computer for writing programs off line and uploading and downloading them to the 8052 BASIC system 10 Tne Microcontroller Idea Book Inside the 8052 BASIC 2 Inside the 8052 BASIC This chapter introduces you to the 8052 BASIC chip including the kinds of projects you can do with it what equipment materials and skills you need in order to design and build an 8052 BASIC project and a pin by pin look at the chip and its abilities Possibilities The 8052 BASIC microcontroller is an easy to use low cost and versatile computer on a chip It s ideal for projects that require more than an assortment of logic gates but less than a complete desktop computer system with a full keyboard display and disk drives If you re interested in doing more with computers than simply running applications programs the 8052 BASIC gives you a chance to design and build a system from the ground up With a few support chips and a program stored in memory yo
261. r reading and writing to the module require just 14 connections or fewer depending on your configuration The HD44780 can control displays of up to 80 characters Learning to program the HD44780 does take some time and experimenting but the result is a useful and flexible display Once you ve had some practice future projects using the displays are simpler and you can reuse or adapt portions of your programs in other projects Many LCD modules use the HD44780 or a compatible controller the OKI M6222 is an example If a module uses the same 14 line interface discussed below chances are it s compatible with the HD44780 About the Modules The character based LCD modules are available from many companies including Philips Optrex and Densitron The surplus market often has good deals Complete technical information on the controller and displays is available from Hitachi and the display manufacturers and from some distributors and catalogs The display of one of these modules contains one or more rows of character positions Each character position consists of a matrix that is typically five segments or dots wide and eight The Microcontroller Idea Book 139 Chapter 8 segments tall The HD44780 can also control matrices that are 11 segments tall for better display of characters with descenders like g p and q The module forms characters by turning on the appropriate segments in a character position For example to di
262. r MTOP in U8 If you have a 32K RAM at U7 storing MTOP will ensure that you can use FPROG and that your stored programs will be preserved when you reboot or power down If U7 is 32K type MTOP 7FFFH FPROG3 Now when your system boots up MTOP will automatically be set to 7FFFh FPROG3 also saves the baud rate and boots to the READY prompt without requiring you to press the space bar If you want to save MTOP and also run a program on bootup use FPROG4 which combines the features of FPROG2 and FPROG3 FPROGS is another useful command It prevents BASIC 52 from clearing external data memory on bootup FPROG6 enables you to add your own assembly language reset routine If you use FRROG2 FPROG6 BASIC 52 will no longer auto detect your host s baud rate You must use the baud rate and crystal value that were in use when you executed the FPROG command Erasing NV Memory Eventually your NVRAM or EEPROM will fill with programs or you may just want to erase what you ve stored and start fresh Listing 4 1 is a program that erases U8 by writing OFFh to all locations To use the program enter the listing and type RUN The READY prompt will return when erasing is complete Line 30 verifies each erasure and is required only for EEPROM Listing 4 1 Erases NVRAM or EEPROM 10 FOR I 8000H TO 9FFFH 20 XBY I OFFH 30 IF XBY I lt gt 0FFH THEN GOTO 30 40 NEXT I 50 END The Microcontroller Idea Book 55 Chapter 4 because of
263. r an intelligent test fixture that ensures that a product meets its specifica tions before it s shipped to a customer At the core of many of these specialized computers is a microcontroller The computer s program is typically stored permanently in semiconductor memory such as ROM or EPROM The interfaces between the microcontroller and the outside world vary with the application and may include a small display a keypad or switches sensors relays motors and so on These small special purpose computers are sometimes called single board computers or SBCs The term can be misleading however since the computer doesn t have to be on a single circuit board and many types of computer systems such as laptop and notebook computers are now manufactured on a single board New Tools To design and build a computer controlled device you need skills in both circuit design and software programming The good news is that a couple of recent advances have simplified the tasks involved One is the introduction of microcontrollers themselves since they contain all of the elements of a computer on a single chip Using a microcontroller can reduce the number of components and thus the amount of design work and wiring required for a project The 8052 BASIC microcontroller even includes its own programming language called BASIC 52 The other development is personal computers themselves A desktop computer can help tremendously by serving as a
264. re available as kits or bare boards if you d rather build your own I ll describe just a few of the available products here see Appendix A for a more complete listing of sources Figure 15 2 Prologic s BASCOM1 is available as a low cost bare pc board with an instruction manual for construction and use 248 The Microcontroller Idea Book Related Products PROLOGIC DESIGNS Figure 15 3 Blue Earth s Micro440 board has BASIC 52 and a monitor program in a tiny package Micromint offers a variety of 8052 BASIC boards and other products Both the BCC52 and RTCS2 are single board systems that can also serve as the base of an expanded system The BCC52 uses edge connectors and a backplane while the RTC52 is a stackable design A variety of expansion boards are available including interfaces to displays keypads relays infrared control and A D converters The BRUTE 52 is a single board with many expansion options on board Micromint s Domino is a complete Basic 52 system in a 20 pin encapsulated package that s about the size and shape of a domino It has a surface mount 80C52 BASIC chip 32 kilobytes each of RAM and EEPROM and twelve I O pins two of which may be analog inputs The Domino s BASIC 52 interpreter adds functions for measuring frequency and period and for reading the analog inputs Prologic Designs offers an inexpensive bare pc board Figure 15 2 and detailed manual for 8052 BASIC systems for those who pre
265. re enable and ALE address latch enable Some of the address lines may also function as control signals that help to select a chip during a memory access 20 Tne Microcontroller Idea Book Inside the 8052 BASIC Code and data memory To understand the operation of the control signals you need to know a little about how the 8052 distinguishes between two types of memory data and code or program memory By using different control signals for each type of memory the 8052 can access two separate 64K areas of memory with each addressed from 0000h to FFFFh and each using the same data and address lines The 8052 accesses code memory when it executes an assembly language program or subroutine Code memory is read only you can t write to it The only instructions that access code memory are read operations Code memory is intended for programs or subroutines that have been previously programmed into ROM or EPROM The 8052 strobes or pulses PSEN when it accesses external code memory Accesses to internal code memory the BASIC 52 interpreter in ROM do not use PSEN or any external control signals Data memory is read write memory usually RAM Instructions that read data memory strobe RD and instructions that write to data memory strobe WR The termdata memory may be misleading because it can hold any information that is accessed with instructions that strobe RD or WR In fact BASIC 52 programs are stored in data memory not code memory as y
266. re is a very simple program to try 10 FOR I 1 to 10 20 PRINT I 30 NEXT I 40 END Enter each of the lines including the line numbers BASIC 52 automatically stores the program in RAM To run the program type RUN You should see this FPuoOwWON AHF WYN HP 0 To view the program lines type LIST The Microcontroller Idea Book 39 Chapter 3 To erase the current program type NEW To verify that the program no longer exists type LIST You can change individual program lines by typing the line number followed by a new statement 10 FOR I 1 to 20 To erase a line type the line number and press ENTER 20 Getting Out of Trouble Occasionally a programming error may cause a program to go into an endless loop or crash the system If it s an endless loop you can exit it and return to the READY prompt by pressing CONTROL C If that doesn t work your only choice is to press S1 to reset the 8052 B ASIC system Resetting will erase the program in RAM so you ll have to re enter it Simple Programs to Try The following sections offer some short programs to try to help you explore your system and become familiar with BASIC 52 Don t worry if you don t understand every line of the programs Later chapters get into programming in more detail Reading Port 1 You can use BASIC 52 to read and write to Port pins 1 8 on the 8052 BASIC The command PHO PORT1 will display the hex value of the entire port Listing 3 1
267. re temperatures from 0 to 250 degrees and each bit in the ADC0848 s output represents a 9 8 millivolt change in the sensor s output The Microcontroller Idea Book 163 Chapter 9 5V LM34 35 V VOUT GND O O O V OmV DEGREE CONNECT TO LMS4 55 VOUT A D CONVERTER S ANALOG INPUT GND vA BOTTOM VIEW EMPERATURE SENSOR LM34 35 TEMPERATURE SENSORS DEVICE ACCURACY RANGE SCALE LM34 1 50 300 E LM34A 0 8 50 300 oF LM34C a ee 40 230 oF LM34D 1 6 EOZ e212 SF LMS5 0 4 a9 Fe OO rc LM35A 0 8 55 50 es LMS5C 0 8 40 Il O C LM35D 0 8 O 100 oC Figure 9 6 The LM34 and LM35 temperature sensors have outputs of 10 millivolts per degree and need no calibration Listing 9 3 Measures and displays temperature reading at ADC0848 s Channel 2 10 REM set A to address of ADC 20 A 0C000H 30 REM use single ended mode 40 REM set C to channel to read 1 8 50 C 2 60 XBY A 8 C 1 70 VREF 2 5 80 B XBY A 90 T INT VREF B 100 255 5 100 PRINT Temperature T 110 PRINT Press any key to take another measurement 120 D GET IF D 0 THEN GOTO 120 130 GOTO 60 140 END 164 The Microcontroller Idea Book Using Sensors to Detect and Measure ee LM385 1 2 LM385 2 5 IK gt VREF 1 2V OR 2 5V M385 1 2 AZ OR dto LM385 2 5 BOTTOM VIEW 5V RI LM385 IK f AF gt VREF 2V R2
268. rithm 10 PRINT TAB 10 5 EEPROM RDY BUSY type 11 INPUT Select Device Type 1 2 3 4 5 gt gt TYPE 12 IF TYPE lt 1 OR TYPE 5 THEN PRINT CHR 7 GOTO 11 20 TYPE TYPE 1 IF TYPE 0 THEN GOTO 1300 21 if type 1 then goto 22 else goto 30 22 INPUT Delay between writes gt gt delay goto 1300 30 ON TYPE GOSUB 2100 2100 2110 2120 2100 40 IF TYPE 2 THEN DBY 38 DBY 38 OR 8 ELSE DBY 38 DBY 38 AND Of7H rem Calculate and store pulse width 50 WAIT 65536 WAIT XTAL 12 DBY 40H WAIT 256 DBY 41H WAIT AND OffH 1300 PRINT Ready to receive the input file one line at a time Set your 1310 PRINT communication software to send a line when when it receives 1320 PRINT the gt prompt PRINT 1330 SOURCE MTOP FREE 1 1340 LINE LINE 1 INPUT s 0 PRINT Validating input buffer 1350 I 1 C ASC S 0 1 IF C lt gt 58 THEN GOTO 3000 REM if not 266 The Microcontroller Idea Book Programs for Loading Files Listing B 2 page 2 of 4 rem Get the byte count and save it in the variable COUNT 1360 I 2 GOSUB 2000 COUNT CH rem Get the starting address for this record s data 1370 FOR I 4 TO 7 STEP 2 GOSUB 2000 ADDR ADDR 256 CH NEXT rem Get the record type we only understand types 0 and 1 1380 I 8 GOSUB 2000 IF CH lt gt 0 AND CH lt gt 1 THEN GOTO 3010 1385 IF TYPE
269. rogram number C R Changes to ROM mode and runs the specified program Default program number is 1 RUN R Executes the current program Clears all variables SGN expression C R Returns 1 if expression gt 0 zero if expression 0 and 1 if expression lt 0 SIN expression C R Returns the sine of expression The Microcontroller Idea Book 83 Chapter 5 SPC expression PRINT option Causes the display to place expression additional spaces besides the minimum two between values ina PRINT statement Example PRINT hello SPC 3 good by hello good by SQR expression C R Returns square root of expression ST expression C R Copies a 6 byte floating point number from the argument stack to external data memory Expression points to the most significant byte of the number STOP Halts program execution STRING expressions expression2 C R Allocates memory for strings variables each consisting of a series of text charac ters Expression Expression2 number of strings 1 Expression2 maximum number of bytes characters per string 1 Executing STRING clears all variables Maximum number of strings is 255 Examples STRING 91 9 reserves space for ten 8 character strings STRING 9 4 reserves space for two 3 character strings T2CON CR Retrieves or assigns a value to the 8052 s special function register T2CON TAB expression PRINT option Specifies the position number of spaces to begi
270. roller Idea Book 45 46 Tne Microcontroller Idea Book Saving Programs 4 Saving Programs In Chapter 3 s experiments the BASIC 52 programs that you wrote were stored in RAM This is fine for temporary use but every time you power down your program disappears and you have to start over This chapter shows you two ways to save BASIC 52 programs more permanently by adding nonvolatile memory to the BASIC 52 system and by downloading your programs to your host system s disk The nonvolatile memory may be battery backed RAM EEPROM or EPROM You can also use this memory for storing assembly language programs or data that you want to save when you power down or reset Disk storage is a convenient way to save programs if you want to edit them off line upload them to a different BASIC 52 system or just save back up copies Nonvolatile Memory Options One of BASIC 52 s handiest features is its programming commands that store programs in nonvolatile NV memory EPROM EEPROM or battery backed RAM The commands assume that the NV memory is addressed beginning at 8000h in external data memory With the addition of NV memory you have two areas that may contain BASIC 52 programs the NV memory addressed beginning at 8000h and the RAM addressed beginning at 0 To distinguish between the two areas you can call the memory beginning at 8000h the EPROM Tne Microcontroller Idea Book 47 Chapter 4
271. rompts you for a bit to set and clear then does so It assumes that you ve stored the current value of E400h in variable A To set a bit line 30 logically ORs the current value with a mask byte that is all Os except for the bit to be set For example to set bit 4 the mask byte is 0001 0000 or 10h which leaves bits 0 3 and 5 7 unchanged but forces bit 4 to be 1 To clear a bit line 40 logically ANDs the byte with a mask byte that is all 1s except for the bit or bits to be cleared For example to clear bit 3 the mask byte is 1111 0111 or F7h The result is that bits 0 2 and 4 7 are unchanged but bit 3 must be 0 Line 50 writes the new byte to the port The Microcontroller Idea Book 97 Chapter 6 Table 6 1 Popular peripheral interface chips 8253 4Programmable Interval Timer Three independent 16 bit counters 6 modes up to 10 Mhz 8255 Programmable Peripheral Interface Three 8 bit I O pins 3 modes direct bit set reset ability 8256 Multifunction Microprocessor Support Controller Asynchronous serial interface baud rate generator five 8 bit timer counters two 8 bit T O ports 8 level interrupt controller programmable system clock 8259 Programmable Interrupt Controller Eight level priority controller programmable interrupt modes 8279 Programmable Keyboard Display Interface Scanned interfaces to 64 contact key matrix and 16 character display The 8255 Programmable Peripheral Interface In addition to the inputs
272. ronics 123 and Digi Key The chips are similar in operation to Motorola s 146026 7 encoder and decoder and you can in fact use them in infrared links as well The encoder and decoder each require just one resistor to set the oscillator frequency 216 The Microcontroller Idea Book Calling Assembly language Routines 13 Calling Assembly language Routines Although BASIC 52 is a convenient programming language that can do a lot sometimes it s just not fast enough for what you need A line in a BASIC 52 program can take many milliseconds to execute and for some applications this is just too long One way to speed things up is to use assembly language This doesn t mean that you have to give up on BASIC 52 entirely You can continue to use it for the parts of your programs that aren t time critical and call assembly language routines only for those parts that have to be fast BASIC 52 can also serve as a convenient development system for loading and testing assembly language routines in RAM and even for programming the routines into NV memory Calling routines from BASIC 52 is a good way to become familiar with assembly language programming Plus through experimenting you can learn a lot about the internal workings of the 8052 chip and how the BASIC 52 interpreter works This chapter explores how and when to interface assembly language routines to BASIC 52 programs An example project connects a digital to analog converter to the
273. rs finer control Bit 4 pin 12 of U2 sets the direction of rotation Ul 12V UDN2993B 8052 BASIC lI LOAD SUPPLY LOGIC SUPPLY PWM P1 22 ENABLE A ENABLE BH P1 H gt PHASE A PHASE BH 4l GND GND GND GNDH DE 9 gu fA OUT 1B DC MOTOR ZOUT 2A OUT 2B MOTOR a BI VEA VEB p DUAL H BRIDGE MOTOR DRIVERS OPTIONAL SECOND MOTOR Figure 11 5 Using a UDN2993 to control a DC motor with pulse width modulation 194 The Microcontroller Idea Book Control Circuits Listing 11 4 Controls direction and speed of a DC motor with BASIC 52 s PWM output 10 PORT1 0FBH 20 T 1 30 INPUT Direction 0 or 1 D 40 INPUT High on pulse width 25 to OFFFFh H 50 INPUT Low off time pulse width 25 to OFFFFh L 60 IF D 0 THEN PORT1 PORT1 AND OFEH ELSE PORT1 PORT1 OR 1 70 PRINT Press any key to end program 80 DO 90 PWM H L T 100 G GET 110 UNTIL G lt gt 0 120 PORT1I PORT1 AND OFBH 130 END You can stop the motor in any of three ways You can bring bits 0 3 of the port low to stop the timer You can bring bit 7 high which removes power from U4 s outputs Or you can bring pins 9 and 10 of U5 high which continues to apply power to the motor but ignores the step input Listing 11 3 prompts you for a motor speed mode of operation and direction and then runs the motor as requested You can stop the program and the motor will continue t
274. rting address of a token table which lists your new keywords At 2070h it expects the starting address of a vector table which lists the assembly language routines that the new keywords execute You may upload both tables to any free area of combined code data memory If you re using an external EPROM programmer you can use code only memory in the 8052 BASIC system In the token table each new keyword is assigned a number in sequence from 10h to 1Fh The name of the keyword is surrounded by quotation marks and a 0 indicates the end of the token The final keyword in the list ends in OFFh to signify the end of the list of tokens Listing 13 7 adds three keywords which toggle set and clear bit 0 of Port 1 The Microcontroller Idea Book 233 Chapter 13 Listing 13 7 page 1 of 2 Creates instructions to set clear and toggle Port 1 bit O in BASIC 52 example program for creating custom commands and instruc tions in BASIC 52 system must contain code memory from 2000h 2079h tokentable equ vectortable equ org db org setb ret org mov ret org mov ret org db db db db db db db db db 234 2100h start address token table 2200h start address vector table 2002h 5Ah at 2002h tells BASIC 52 5ah to call 2048h see below 2048h Set bit 45 to tell BASIC 52 that custom commands or 45 instructions have been added 2078h stores starting address of dptr tokentable token table 2
275. s minutes hours and even days months and years You can use the clock to trigger operations at specified intervals such as every five minutes hourly daily on the first of the month or whatever Or a data logger might record the time and date of each measurement it takes or the times when it detects selected events BASIC 52 includes its own real time clock that counts in 5 millisecond increments For many timing tasks this is all you ll need Another approach is to add a timekeeping chip that automatically keeps track of time and calendar information Many clocks perform functions beyond simple timekeeping such as generating periodic interrupts or acting as a watchdog that resets the microprocessor in case of program crashes Plus using a separate timekeeping chip means that you don t have to devote any of the 8052 BASIC s resources to the task This chapter describes how to use both BASIC 52 s real time clock and Dallas Semicon ductor s DS1286 Watchdog Timekeeper chip BASIC 52 s Real time Clock The 8052 BASIC like other computers has a timing crystal or another frequency source connected to its XTAL pins In fact the chip will do nothing at all without this input since it is what clocks instructions into the chip s CPU for execution While this clock provides Tne Microcontroller Idea Book 171 Chapter 10 an essential timing reference by itself it doesn t keep track of real world time measured in seconds
276. s NAO AQ 82 C 55 INTRB PC 1 BEB OBFB PC STBB ACKB PC INTRA PC STBA PC I BFA PC gt O N gt x OBFA PC PAS PA PA PA PA PA PA PA NOW KRWN O GW N PB PB PB PB PB PB PB FB NOW KRWN PC NOW KR WN W Bh o lm wits O S GW co PORT A NO PRN RN ROT RN KRIWI N o PORT B PORT C LOWER N SQ Hl wlNloa u as WN PORT C UPPER PER PHERAL INTE RFACE POWER AND GROU D PINS 5V GND Figure 6 6 Connections for adding an 8255 Programmable Peripheral Interface crystal frequency of an 8085 interfaced to the 8255 Because the signal timings for an 8052 are very different these ratings don t apply and you have to look at the timing diagrams to determine what will work For use with the 8052 BASIC use a 5 Mhz or faster 8255 if your crystal is 12 Mhz Slower crystals can use the 3 Mhz or 5 Mhz versions 102 The Microcontroller Idea Book Inputs and Outputs An 8255 Interface Figure 6 6 shows an 8255 U15 accessed at FCOOh in the 8052 BASIC system Many of the pins connect directly to matching signals in the system D0 D7 connect to the system s data bus A0 and A1 connect to the lowest two address lines and the RD and WR inputs connect to U2 s matching outputs CS connects to pin 7 of U11 from Figure 6 2 wh
277. s Siemens Dallas Semiconductor OKI Fujitsu and Harris Matra now also make 8051 family chips Some companies have expanded the 8051 family by offering compatible chips with additional features Table 2 1 summarizes the differences among popular 8051 family chips The 8052 is an enhanced 8051 with an extra timer and more RAM and ROM The 8031 and 8032 are identical to the 8051 and 8052 except that the ROM area is unused and program code must be stored in an external EPROM or other memory chip The 8052 like other 8051 family chips is available in NMOS and CMOS versions Figure 2 2 shows the pinout of the 8052 and 8052 BASIC and Table 2 2 describes the pin functions 16 Tne Microcontroller Idea Book Inside the 8052 BASIC BASIC 52 FUNCTIONS T2 P1 0 Q VCC T2 EX P1 1 42 PO ADO PWM OUT P1 2 Q3 P 1 ADI ALE DIS P 3 44 PO 2 AD2 PGM PLS P 4 5 PO 3 AD3 PCM E P1 5 Q6 P 4 AD4 DMA ACK P1 6Q7 PO 5 AD5 LPT OUT P1 7 Q8 PO 6 AD6 RESET 9 P 7 AD SER I RXD P3 0 EA SER OU TXD P3 1 l ALE DMA RE INTO P3 2 2 PSEN INTI P3 3 3 P2 7TLALD TO P3 4 4 P2 6 A14 TAP S25 5 P2 5 A13 WR P3 6 6 P2 4 A12 RD P3 7 7 P2 3 A1 1 XTAL2 8 P2 2 A1 XTAL 9 P2 1 A9 VSS 20 P2 0 A8 8 52 BASIC 40 PIN DIP Figure 2 2 Pin functions of the 8052 and 8052 BASIC microcontrollers Elements of the 8052 and 8052 BASIC These are the major elements of
278. s and recommendations for selecting values for these components For best performance use components with 5 or tighter tolerance With the values shown the oscillator s frequency is 1 kilohertz which is at the low end of Motorola s recommended range for the chip With this frequency the narrowest transmitted pulses are 500 microseconds wide I chose this pulse width to be compatible with the requirements of the infrared module in the receiver circuit which may not respond reliably at higher frequencies If you have an oscilloscope or frequency counter you can monitor the oscillator frequency at U1 s pin 12 For each transmission the encoder sends all nine address and data bits in sequence waits three data bit times 24 milliseconds at 1 kHz and then repeats the entire transmission A complete transmission requires 182 milliseconds from the time that TE goes low If you hold TE low the encoder will transmit continuously Otherwise the transmission ends after sending the information twice The encoder s output drives infrared emitting diode IRED1 Instead of directly driving the IRED with the encoder s output DATA OUT NAND gate U2B combines DATA OUT with a 40 kHz oscillator The result is that the encoder s pulses transmit as bursts of 40 kHz pulses As we ll see the infrared receiver is designed to reject stray signals that don t pulse at 40 kilohertz Pulsing the IRED also saves power since the IRED is never on constantl
279. separate ground paths for analog and digital signals In Figure 9 4 this means that AGND and any ground connections related to the analog inputs or VREF should be wired together but kept separate from the ground connections for the digital circuits including logic chips the 8052 BASIC and memory chips The two grounds are tied together at one place only as near to the power supply as possible The schematic uses 160 The Microcontroller Idea Book Using Sensors to Detect and Measure different ground symbols for the two ground paths Also be sure to include decoupling capacitors at pins 10 and 12 Measuring Modes To allow for different circuit requirements the ADC0848 offers a choice of three software selectable modes of operation single ended differential and pseudo differential Figure 9 5 illustrates In single ended mode each analog input is referenced to AGND This is the simplest mode and will work fine for many applications Listing 9 2 causes the ADC to convert each of the eight channels in turn and displays the results on the host computer For testing the circuits you can connect a the wiper of a potentiometer to each channel with the other two leads connecting to AGND and VREF Verify that the readings for each channel vary from 0 to 255 as you vary the input voltage The other modes are useful for more critical measurements where you need to reject background noise or offset voltages In differential mode each cha
280. sistor s value For example 2 25V 150 ohms 0 015 amperes or 15 milliamperes Both LSTTL and HCMOS devices are capable of 20 milliampere output currents At these higher currents the output voltage isn t specified but should be enough to light an LED To turn on an LED at a port write a 1 or 0 as appropriate to the bit that controls it as described in Chapter 6 Listing 8 1 assumes that you have eight LEDs connected to the 126 The Microcontroller Idea Book Displays 74HC374 0 OFF 1 0 ANY Q OUTPUT A we LED R1 0 0 ANY 1 C PORT i OUT PUT E ANY AS LE HCMOS OUTPUT RI 74 74 HC374 ANY Q ANY D PORT R1 VALUES FOR 15mA LED CURRENT LED COLOR R RED 180 GREEN 150 YELLOW 150 BLUE 50 OUT PUT LS374 5V O K A LED RI ON ANY HCMOS OR LST Ko lt OUT PUT OFF A LED RI Q ON T gt QFF OUT PUT TL Figure 8 1 LED interfaces to output ports Use an HCMOS output if you want a high output to turn on the LED Use either HCMOS or LSTTL if you want a low output to turn on the LED The Microcontroller Idea Book 127 Chapter 8 Listing 8 1 Controls eight LEDs at an output port 10 A 0E000H REM address of LEDs 20 L OFFH REM initial control value for LEDs 20 XBY A L REM turn off all LEDs 30 DO 40 INPUT Select an LED 0 7 B 50 INPUT Turn on or off 0O off l
281. splay an L the module turns on one vertical column and one horizontal row of segments For most characters the bottom row is reserved for displaying a cursor which leaves 35 segments to form the character Displays are available in several sizes Popular sizes are 1 x 16 1 line of 16 characters 2 x 16 and 2 x 20 Displays larger than 80 characters require supplemental driver chips along with the HD44780 but the displays can use the same interface Table 8 1 summarizes the signals in the 14 line interface Power Supplies and Backlights The power supply pin 2 is a simple 5V DC The modules contain their own oscillators to drive the LCD segments Typical power consumption for an entire module is just a couple of milliamperes A contrast input pin 3 allows you to adjust for best viewing under varying light conditions viewing angles and temperatures Some LCD modules use backlighting to allow viewing in dim light A module may be reflective which does not use backlighting transmissive which must use backlighting or transflective which may use backlighting or not With a transflective display you can add a switch to enable users to turn the backlighting on or off as desired One popular type of backlight is an electroluminescence EL panel behind the LCD segments An EL panel emits a diffuse light that provides a bright background for the LCDs Electroluminescent backlighting requires first of all a module that contains an EL pa
282. t an ordinary OR gate it s a 75453 peripheral driver Unlike ordinary logic gates U10 s open collector output can pull up to 30V without damaging the chip The output also has much greater current sinking ability than other logic gates up to 300mA and can easily provide base current to drive transistor Q1 When pin 3 of U10A is high Q1 is off and VPP connects to 5V through germanium diode D2 The diode s voltage drop is just 0 3V so VPP is actually at about 4 7V Intel s data sheets specify that read operations require VPP to be at least 3 8V for the 2764A or VCC 0 7V for the 27C64 so 4 7V is within the specifications 58 The Microcontroller Idea Book Saving Programs CIRCUITS FOR EPROM PROGRAMMING WITH PROG COMMANDS 5 MSEC PROGRAMM NG 12 5V 5V O O Ql es PN297 ee 1N27 75453 PERIPHERAL DRIVER e J5 FCA R12 TO U8 PIN 1 EPROMIS ZT 2 1 uF 10K VPP 2 NVRAM EEPROM O NO CONNECTION p 5V TO UB PIN 28 VCC ADDITIONAL CIRCUITS FOR EPROM PROGRAMMING WITH FPROG COMMANDS INTELLIGENT PROGRAMMING 6V 5V R14 10K PGM GM EN 32 SZ PN2907 D2 RESET T 75453 PERIPHERAL DRIVER oe J6 R15 EPROM FPROG O 10K TO U8 PIN 28 VCC o EPROM PROG NVRAM EEPROM 5V Figure 4 5 Additional circuits for programming EPROMs The Microcontroller Idea Book 59 Chapter 4 Table 4 2
283. t it s acommon and flexible one In the schematic each output is labeled with the base or bottom address in the block it controls For example when U2 reads or writes to an address between 0 and 1FFFh in external memory A13 A14 and A15 are low so pin 15 of U6 is low For all other addresses pin 15 is high If we connect pin 15 to the chip select input of an 8K RAM the RAM will be enabled only when addresses from 0 to 1FFFh are accessed Remember that 8K or 8 kilobytes is 2000h or 0 through 1 FFFh in hexadecimal If you use a 32K RAM you don t need U6 to decode its addressing For all of the 32K RAM s addresses 0 to 7FFFh A15 is low and for all other addresses 7FFFh to FFFFh A15 is high This means that you can use A15 directly as a chip select without additional decoding U6 will come in handy later however even if you use a 32K RAM RAM choices The minimal circuit includes just one memory chip U7 which can be an 8K or 32K static RAM or SRAM BASIC 52 requires at least 1K of RAM but I ve used the larger capacities since the extra room is useful and doesn t cost much more The pinouts of the two chips are similar with jumpers J2 and J3 routing the signals that vary The 8K chip has 13 address inputs A0 A12 while the 32K chip has 15 A0 A14 Eight data T O pins 1 01 1 08 connect to the data bus and hold the bytes to be read or written The RAM has three control inputs whose functions match those of th
284. ta inputs D0 D7 into an analog voltage D0 D7 are controlled by an output port at E400h You may change this address to match any output port on your system Listing 13 4 Sine wave generator for Figure 13 2 s circuit 10 REM Begins by calculating and storing sine values 20 REM for 256 locations along a sine wave 30 REM Line 100 converts a position in the sine wave 40 REM 0 255 to the radians required by the sine 50 REM operator 0 0246 2 PI 256 Adding 1 to the 60 REM sines makes all values positive from 0 to 2 70 REM Multiplying by 127 5 results in values that 80 REM range from 0 to 255 90 FOR I 0 TO 255 100 XBY 3000H I INT SIN I 0246 4 1 127 54 5 110 NEXT I 120 PRINT Sine values are stored in RAM 3000h 30FFh 130 PRINT Press Control C to quit 140 REM Write the values in sequence to E400h 150 DO 160 FOR I 3000H TO 30FFH 170 XBY 0E400H XBY I 180 NEXT I 190 WHILE 1 1 200 END The Microcontroller Idea Book 227 Chapter 13 The DAC is configured in its flow through and voltage switching modes In flow through mode the analog output continuously reflects the data inputs The chip has several control signals for latching inputs and outputs but these aren t needed by our circuit In voltage switching mode the analog output is a voltage proportional to the value of the byte formed by DO D7 An LM385 2 5 volt reference is applied across current output terminals IOUT and IOUT2 and the
285. tatement causes the program to jump back to the program line following the GOSUB statement 66 Tne Microcontroller Idea Book Programming Subroutines have two advantages First they help you to break up your program code into discrete units with each having a specific purpose This makes the program code easier to debug and easier to understand in general especially if you return to it a week month or year after writing it when the details are no longer fresh in your mind Second subroutines make it easier to reuse your code if you have a similar task in another project For example all or most of the code involved with controlling a display module can usually be written as a subroutine or perhaps a series of subroutines This way if you want to use the same display module in more than one project you can reuse the code without having to pick through your previous programs to find the program lines that you need e Keep program lines short Short lines are easier to edit with BASIC 52 s line editor which requires retyping the entire line to make a change They re also easier to read If you upload programs from disk shorter lines can eliminate problems caused by BASIC 52 s not having enough time to process each line before the next one arrives Although BASIC 52 allows you to place multiple statements on one line with up to 79 characters per line shorter is better There are two situations where you might want to combine a seri
286. tch connections are arranged in a rectangular array Figure 7 7 illustrates a typical hex keypad that uses matrix encoding There are four rows Y and four columns X to which the switches connect Each key corresponds to a hexadecimal digit 116 The Microcontroller Idea Book Switches and Keypads 1 K PULL UPS ANY INPUT PORT BIT SWITCH A A j BIT 1 SWITCH B B H g BIT 2 SWITCH C CH e _ _ _ _ BIT 3 SWITCH D D H 5 BIT 4 SWITCH E E BIT 5 SWITCH F g BIT 6 SWITCH G G i BIT 7 SWITCH H H F common ak INPUT BIT MEANS 8 KEY CORRESPONDING SWITCH LINE PER KEY LS PRESSED KEY PAD Figure 7 6 A line per key keypad is a series of momentary switches with each switch having a common terminal In this keypad each key acts as a normally open pushbutton whose contacts connect one row and one column when the key is pressed In Figure 7 7 pressing key 1 connects Y1 and X1 pressing key 2 connects Y1 and X2 and so on down to key F at Y4 X4 By determining which row and column are connected you can detect which key has been pressed Matrix encoding saves on hardware since each key doesn t require a dedicated signal line With Figure 7 7 s keypad you can detect any of 16 key presses with 8 signal lines Sixteen keys is a popular size for keypads but larger and smaller sizes are
287. tel s or Systronix s programming manual and a data book from Intel or another 8052 vendor See the Product Vendors section for addresses and phone numbers BASIC 52 Programming Systronix 20 postpaid Complete reference to the BASIC 52 programming language Includes many program ex amples and handy back cover index The Microcontroller Idea Book 251 Appendix A BASIC 52 User s Manual Intel 270010 004 15 Complete reference to the BASIC 52 programming language Includes some circuit sche matics Embedded Microcontrollers Handbook Intel 22 95 Intel s handbook or data book has hardware details and an assembly languuage refer ence for the 8052 and 80C52 and much more but nothing specifically about the 8052 BASIC chip Intel updates the data books yearly so the exact title and price may vary Ask for the data book that covers 8 bit embedded controllers Philips Siemens and other manufacturers also publish data books for their 8052 and 80C52 chips 8051 2 Microcontrollers These are some additional books about the 8051 family of microcontrollers The Product Vendors list has addresses and phone numbers for many of the publishers Local bookstores can order the others which are from major publishers Assembly Language Programming L S Electronic Systems 190 pages 33 00 For the 8051 family C and the 8051 Programming and Multitasking by Thomas W Schultz Prentice Hall 1993 52 Discusses using an
288. tem Turn on its power supply and press the SPACE bar at the host s keyboard You should see this BASIC 52 sign on message and prompt MCS 51 tm BASIC V1 1 READY Figure 3 6 shows the sign on message and a simple program using Windows Terminal accessory for communications Troubleshooting If you don t see the prompt it s time to troubleshoot Getting the system to boot up the first time can be the most challenging part of a project especially when serial communications are involved Here are some things that may help you isolate the cause of the problem e Try again by pressing and releasing S1 and pressing the space bar If you are using a 32K RAM for U7 BASIC 52 requires about 1 second to perform its memory check after a reset before it will respond to the space bar With an 8K RAM the delay is a few tenths of a second proportionately longer with slower crystals e Double check the easy things Are the communications parameters correct Did you select the correct serial port Are all ICs inserted e Verify that pin 9 of U2 goes high then low when you press and release S1 e Check the power and ground pins of all ICs for proper voltages e Connect a logic probe to pin 10 of U2 When you press the space bar you should see the logic level toggle as U2 receives the ASCII code for a space 20h If not you probably have a problem in the setup of your communications software or in the serial cabling e Verify that
289. terials To build the circuits you ll need circuit construction materials and the skills to use them Wire wrapping is an effective quick way to build the circuits described but if you prefer you can use point to point soldering or design and make a printed circuit board or use any method that you re comfortable with Another option is to buy one of the available kits or prebuilt 8052 BASIC boards You can then use this book as a guide to using and expanding the abilities of your board Appendix A lists board suppliers and books on project construc tion techniques Documentation Using just the information in this book you can build and begin using your system For serious experimenting two additional references are recommended programming and 14 The Microcontroller Idea Book Inside the 8052 BASIC hardware manuals For programming you have two choices Intels BASIC 52 User s Manual or Systronix s BASIC 52 Programming Each of these describes the BASIC 52 programming language in detail The Intel manual includes a few schematics while Systronix s version has more programming examples and is better organized in general Intel s Embedded Microcontrollers data book is a hardware reference that describes the 8052 chip including electrical specifications and timing requirements It also includes an as sembly language reference Appendix A tells where to get these Other useful documentation includes data sheets for the other c
290. tes of DD RAM aren t needed you can use the spare DD RAM as general purpose RAM Reading and Writing Writing to the LCD module involves the following steps Bring RS high to write data or low to write an instruction Bring R W low Bring D0 D7 to their desired states Wait at least 140 nanoseconds Bring E high for at least 450 nanoseconds Bring E low The Microcontroller Idea Book 143 Chapter 8 CHARACTER DOT MATRIX LCD MODULE BASED GND 5V RS R W O DO D D2 D3 D4 D5 D6 RI WIM SON SZEGNI PC 4 PC 6 12 PCLS pa oli PA 1 5 PA 2 i PAGES 40 PA 4 39 PA 5 38 PA 6 37 PA 7 FOR WRITE ONLY INT FOR MAXIMUM DISPLAY CONTRAST D7 CONTRAST TIE PIN 3 0 PIN 5 OF LC R AC TI J D MODUL F LCD MODULE TO GND E TO GND Figure 8 9 Using an 8255 to control a character based LCD module Read operations are similar to writes with R W high instead of low The data appears on D0 D7 in 320 nanoseconds or less after E goes high The HD44780 cannot accept a new instruction until it has finished executing its previous instruction Table 8 2 shows the maximum time each instruction requires BASIC 52 is slow enough that you don t have to worry about the required delays If you re using an assembly language routine your program must include delays after each instr
291. that the assembler found no errors that prevented it from creating the object file If you do see error messages you ll have to find out what s wrong before continuing The listing file also includes the error messages and these should help you track down any problems Table 13 1 An Intel Hex file consists of a series of records each of which contains the the six elements below Name Chars Description Record Mark 1 Each record begins with a colon Record Length 2 Number of data bytes in the record Address Field 2 In data records the address where the first data byte is to be stored with following bytes in sequence In other record types 0000 Record type 2 There are four record types 00 Data 01 End of File 02 Extended address 03 Start address Data Field varies Contents depends on the record type 00 Data to be programmed 01 Not used empty 02 Segment For address fields larger than 64K data is stored beginning at segment 10h address field 03 Start address of program Often unused Checksum 2 To calculate the checksum 1 Add the values of all of the bytes in a record 2 Take the 2 s complement of the result Complement all bits and add 1 3 The checksum is the low byte of the result 224 The Microcontroller Idea Book Calling Assembly language Routines Successful assembly is a good sign but it doesn t mean that the program is error free As in any programming language a line of code may c
292. the 8052 plus the enhancements included in the 8052 BA SIC CPU The CPU or central processing unit executes program instructions Types of instructions include arithmetic addition subtraction logic AND OR NOT data transfer move and program branching jump operations An external crystal provides a timing reference for clocking the CPU ROM ROM read only memory is the read only memory that is programmed into the chip in the manufacturing process In the 8052 BASIC the ROM contains the BASIC 52 interpreter program that the 8052 executes on boot up As far as the hardware is concerned this is the only difference between the ordinary 8052 and the 8052 BASIC The Microcontroller Idea Book 17 Chapter 2 Table 2 2 page 1 of 2 Pin functions of the 8052 microcontroller and 8052 BASIC additions Pin Symbol Input 8052 8052 BASIC Additions Output Function Symbol Funcion 1 P1 0 VO Port 1 bit 0 T2 Timer 2 external input 2 P1 1 VO Port 1 bit 1 T2 EX Timer 2 external reload capture 3 P1 2 VO Port 1 bit 2 PWM Pulse width modulated output 4 P1 3 VO Port 1 bit 3 ALE DIS Address latch disable 5 P1 4 VO Port 1 bit 4 PGM PLS Program pulse 6 P1 5 1 0 Port 1 bit 5 PGMEN Programming voltage enable 7 P1 6 VO Port 1 bit 6 DMAACK DMA acknowledge 8 P1 7 VO Port 1 bit 7 LPT Line printer out 9 Reset Input Reset system 10 P3 0 VO Port 3 bit 0 SER IN Serial port in RXD Serial receive 11 P3 1 VO Port 3 bit 1 SER OUT Seri
293. the desired output or use 1 tolerance resistors for a more precise output You can wire the LM317 circuits to your 8052 BASIC circuit board and add terminals or jacks for connecting a 15V supply Wire the LM317 s output to the appropriate connections in Figure 4 5 Switching Regulators A third way to generate programming voltages is to use switching regulators like those available from Maxim Semiconductor These can create the programming voltages from your 5V supply For example the MAX633 can create outputs of 6 and 12 5V from a 5V 62 Tne Microcontroller Idea Book Saving Programs supply The chip requires an additional inductor and capacitor plus two resistors to set the output voltage Maxim s data books have more details about this and similar chips Storing Programs on Disk With BASIC 52 s ability to store programs in on board memory disk storage isn t necessary But storing programs on the host system s disk is convenient since you can save as many programs as you want without worrying about running out of program memory Since the programs are stored as ASCII text you can write or edit them with any text editor and then upload them as needed to the target system Most communications software allows you to upload and download files In Procomm Plus you use the PGUP and PGDN keys In the Windows Terminal Accessory use the Transfers menu Uploading to the 8052 BASIC System When you upload a program to the
294. the key that is pressed For example if X3 and Y2 are low at the same time key 6 has been pressed A Keypad Encoder An easy way to interface a matrix encoded keypad to the 8052 BASIC is to use National Semiconductor s 74C922 16 key encoder chip or the 74C923 which handles up to 20 keys Figure 7 8 shows the pinout truth table and waveforms of the 74C922 The chip is a member of the 74C family which uses CMOS technology but TTL type part designations like the HCMOS family but not high speed The chip is available from many parts sources The 74C922 has several useful features e It automatically translates each keypress into a 4 bit number 0000 to 1111 The chip has four inputs Y1 Y4 and four outputs X1 X4 that connect to the X and Y lines on a keypad and 4 data outputs A B C D that identify the key that was pressed The 74C922 contains its own scanning circuits including internal row pullups All you need to add is a capacitor at the OSC input to set the scanning frequency or you can use an external clock to control the scanning e Keypresses are signaled automatically by a Data Available DA output which goes high when a key is pressed You can tie DA to an interrupt or port pin on the 8052 BASIC The Microcontroller Idea Book 119 Chapter 7 a OSCI E Y BOUNC COL COL DATA OUTPUTS SWITCH D YI XI YI X2 Yla XS YI X4 Y
295. the options include using machine code assembly language or a higher level language Which programming lan guage you use depends on things like desired execution speed program length and convenience as well as what s available in your price range Machine code The most fundamental program form is machine code the binary instruc tions that cause the CPU to perform the operations you desire Assembly language One step removed from machine code is assembly language where abbreviations called mnemonics memory aids substitute for the machine codes The mnemonics are easier to remember than the machine codes they stand for For example in the 8052 s assembly language the mnemonic CLR C means clear the carry bit and is easier to remember than its binary code 77000011 Since machine code is ultimately the only language that a CPU understands you need some way of translating assembly language programs into machine code For very short programs you can hand assemble or translate the mnemonics yourself by looking up the machine codes for each abbreviation Another option is to use an assembler which is software that runs on a desktop computer and translates the mnemonics into machine code Most assemblers provide other features such as formatting the program code and creating a listing that shows both the machine code and assembly language versions of a program side by side Higher level languages A disadvantage to assembly languag
296. til you release the switch Level triggered interrupts can be useful if you have multiple interrupt sources If each source generates an interrupt request by turning on an open collector output you can tie all of the The Microcontroller Idea Book 113 Chapter 7 5V Cl sit R luF 478k 1 I Z2 R 74HC14 il IL Ga NL p a Figure 7 3 A hardware debouncing circuit using a 74HC14 Schmitt trigger inverter outputs together and the combined output will be low when any interrupt source is active To enable the 8052 BASIC to identify the interrupt source each source can also set a port bit Latching the interrupt requests with a flip flop for example will ensure that no requests are missed The 8052 BASIC can clear the latch by writing to another port bit when it identifies the source For level triggered interrupts use this statement to clear bit 2 of the TCON register TCON TCON TCON AND OFBH To return to edge triggered use this statement to set bit 2 of TCON TCON TCON TCON OR 4 Polling When you don t want to use an interrupt an alternate way to detect a keypress is by polling which consists of having the program check periodically to see if the switch has been pressed In a program that prompts for input and then waits for the user to press a key you can poll continuously until you see a response Listing 7 2 is an example that assumes that you have two normally open pushbutto
297. ting to be read INTR can connect to an interrupt input on the 8052 BASIC pin 13 for example to cause it to jump to an interrupt routine that reads The Microcontroller Idea Book 107 Chapter 6 the newly latched data The falling edge of RD brings INTR low again as the CPU reads the data Output Control For output ports in Mode 1 there is a complementary set of signals OBF output buffer full output goes low to indicate that the CPU has written data to U12 OBF can signal a peripheral device a display for example that it s time to read data that the 8255 is holding for it ACK acknowledge input strobes low to tell the 8255 that the peripheral device has read the data ACK s falling edge brings OBF high INTE interrupt enable is set to enable INTR Its function is similar to its function for Mode 1 s inputs except that Group A uses bit 6 of Port C and Group B uses bit 2 of Port C INTR interrupt request output goes high to signal that a peripheral has accepted the data written to U12 The falling edge of WR brings INTR low and INTR goes high again when ACK and OBF are both high and INTE is set to signal that the peripheral has read and acknowledged the data For both inputs and outputs connecting INTR is optional Mode 1 leaves two bits of Port C unused If Port A is input the unused bits are 6 and 7 If Port A is output the bits are 4 and 5 You can use these as general purpose inputs or outputs Bit 3 of th
298. tional Semiconductor has a good selection of books covering most types of integrated circuits The exact titles and prices change from year to year but this is a typical selection CMOS Logic including HCMOS HCTMOS 4000 series 74C series TTL Logic including LSTTL Linear Devices A D D A temperature sensors voltage references Op Amps Power ICs voltage regulators peripheral drivers You can request data books directly from the manufacturers Digi Key and other component vendors also offer a selection For a small charge many suppliers will include data sheets for individual components that you order Related Topics These are some other books that you may find useful in designing building and working with microcontroller circuits The Art of Electronics second edition by Paul Horowitz and Winfield Hill Cambridge University Press 1989 59 95 A complete and readable reference on electronic circuits of all types Gordon McComb s Tips and Techniques for the Electronics Hobbyist by Gordon McComb TAB McGraw Hill 1991 A good introduction to building testing and understanding electronic circuits Making Printed Circuit Boards by Jan Axelson TAB McGraw Hill 1993 19 95 How to design and make pc boards with a chapter on wire wrapping and other construction methods The Microcontroller Idea Book 253 Appendix A BBS s Use your personal computer and communications software to explore these BBS s on line
299. to a different output of U11 Since U12 is read only and U14 is write only you could use the same address for both by having them share the same output of U11 For example if you wire both pin 2 of U13A and pin 4 of U9B to pin 7 of U11 both will be accessed at FCOOh Write operations will access U12 and reads will access U14 In this way you can add up to eight input ports and eight output ports with eight chip select addresses in all Wiring Tips Add Figure 6 2 s circuits to Chapter 3 s circuits including the connections shown to DO D7 A10 A12 E000h READ and WRITE in the main circuit The schematic continues the component numbering sequence from the earlier schematics Use sockets for the ICs Wire U13 s unused inputs pins 5 6 8 9 11 and 12 to GND or 5V Also add a couple of 0 1 microfarad ceramic decoupling capacitors from 5V to GND near the added ICs 92 Tne Microcontroller Idea Book Inputs and Outputs If you wish you can wire U14 s inputs and U12 s outputs to headers for easy access when you want to connect clip on jumpers probe leads or ribbon cables to the inputs and outputs Basic Tests What can you do with these new inputs and outputs First some simple tests You read and write to the ports exactly as you read and write to external memory This BASIC 52 statement will display the value of the byte at U12 s inputs PRINT XBY 0E000h Or you may prefer a hexadecimal display PHO XBY 0E00
300. to latch data into U15 and save it until the 8052 BASIC has time to read it In Mode 1 you can configure Ports A and B to be inputs outputs or one of each Each port has its own set of handshaking signals on Port C as described in Table 6 2 Input Control For input ports these are the added signals STB strobe input causes data to load into the 8255 s input latch In Mode 1 the 8052 B ASIC can t read the data at U15 s ports until STB s rising edge latches the data in You can use an output of a clock or counter chip to latch data into U15 at timed intervals or latch data when a user presses a key IBF input buffer full output goes high to indicate that the 8255 has loaded data in response to STB When the 8052 BASIC reads the data the rising edge of RD brings IBF low again You can use IBF to clear or reset the device that generated STB INTE interrupt enable is an internal signal that you must set to enable INTR described next For Group A you set INTE by writing 1 to Port C bit 4 For Group B write 1 to Port C bit 2 The BASIC 52 statement to set INTE for Port A is this XBY OF03h 9 For Port B it s this XBY OF03h 5 Writing to these locations sets internal bits in U12 However these write operations have no effect on the STB inputs which share the same bit addresses at Port C INTR interrupt request output goes high when INTE is set and both STB and IBF are high to signal that the 8255 has data wai
301. to monitor and control devices outside of these circuits The options include low cost buffers and latches as well as programmable chips with features like individual bit control automatic generation of control signals and the ability to configure a port as input output or bidirectional The Memory Map But before we start adding components it s time to draw a memory map for the system The memory map is a diagram that shows the range of addresses a microcontroller or other computer can access along with each component that the computer reads or writes to and the addresses where each component resides The components may be memory chips like RAM or EPROM or they may be other components that the computer accesses by specifying an address Drawing a memory map helps to ensure that each component has a unique address or range of addresses Figure 6 1 shows the memory map for our design Each 64K area of external memory consists of eight 8K blocks Remember that 8 kilobytes equals 8192 in decimal but 2000 in hexadecimal The Microcontroller Idea Book 87 Chapter 6 Internal code memory consists of the 8052 BASIC s ROM which uses the addresses from 0 to 1FFFh External data memory beginning at 0 is also required BASIC 52 reserves the first 512 bytes for its own use and it stores the current BASIC 52 user program immediately above this area The memory map allows a choice of using an 8K RAM from 0 to 1FFFh or a 32K RAM which uses
302. to write run and test your programs quickly With over 100 commands instructions and operators BASIC 52 is more capable than other microcontroller BASICs And as a member of the 8051 microcontroller family the 8052 BASIC has a standard popular architecture The ideas and applications presented here are not limited to the 8052 BASIC however If your favorite chip is a different one you can adapt the circuits and programs to it The schematics and program listings in this book include comments and explanations to help you apply the ideas whether or not you are using the 8052 BASIC vii Introduction What s Inside This is not just a textbook that presents information but glosses over the details of how to apply it Inside you ll find practical information including the following e Complete circuit schematics and parts lists so you can easily build the circuits yourself e Design theory for example why use this particular component or how can I expand or modify the circuit shown e Example program listings for easy testing and use of the circuits e Construction and debugging tips to help you get the circuits up and running without problems The appendices include a complete list of sources to help you find the components and additional information you need for your projects Because microcontroller projects involve both circuit design and programming I cover both the hardware and software aspects The book be
303. tors that connects from the crystal to ground Temperature variations will cause a crystal s frequency to drift Crystal accuracy is rated in parts per million per degree Celsius often shortened to ppm Over time a crystal rated at 10 ppm should vary no more than 0 001 percent per degree Celsius or 0 86 seconds per day if the temperature varies no more than 1 degree Celsius If your clock must be super accurate choose the most stable crystal you can find and and avoid temperature fluctuations You might think that you can get a more accurate real time clock by adjusting XTAL to match your crystal s actual frequency rather than its rated value You could measure the crystal s frequency with a frequency counter or experiment by varying the value of XTAL and monitoring the real time clock to find the best match For example if your 12Mhz crystal actually oscillates at 11 97 Mhz you could set XTAL equal to 11970000 172 The Microcontroller Idea Book Clocks and Calendars Listing 10 1 Uses BASIC 52 s real time clock to count seconds minutes and hours 10 REM set XTAL to match your crystal s frequency 20 XTAL 12000000 30 REM set and initialize clock 40 GOSUB 200 50 REM increment clock variables once per minute 60 DO 70 ONTIME 60 500 80 WHILE 1 1 90 END 200 PRINT Please enter the current time 210 INPUT AM 0 or PM 1 AP 220 INPUT Hour 1 12 H 230 INPUT Minutes 0 59 M 240 IN
304. tronic components 261 Appendix A Universal Cross Assemblers 8051 assembler P O Box 6158 Saint John NB E2L 4R6 Canada 506 847 068 1 262 The Microcontroller Idea Book Programs for Loading Files Appendix B Programs for Loading Files This appendix contains the BASIC 52 programs HEX2RAM BAS and HEXLOAD BAS described in Chapter 13 Use HEX2RAM BAS to load an Intel Hex file from your host computer to RAM including battery backed NV RAM The HEXLOAD BAS program does the same but also allows you to load the file into EEPROM or EPROM HEX2RAM uses XBY while HEXLOAD uses PGM and is slower The Microcontroller Idea Book 263 Appendix B Listing B 1 page 1 of 2 HEX2RAM BAS loads Intel Hex files from a host computer to memory in the 8052 BASIC system Reprinted with permission from Systronix 10 STRING 82 80 DIM HI 70 DIM LOW 70 15 FOR I 48 TO 57 HI I I 48 16 LOW I I 48 NEXT 25 FOR I 65 TO 70 HI I I 55 16 LOW I I 55 NEXT 35 PRINT TAB 19 INTEL HEX FILE TO RAM LOADING PROGRAM V1 1 45 PRINT TAB 14 Copyright 1991 Systronix Inc All rights reserved PRINT 55 PRINT TAB 8 This program accepts as input an Intel hex file and stores 65 PRINT TAB 8 it in external RAM at the addresses speci fied in the HEX file PRINT 75 PRINT TAB 8 Ready to receive the input file one line at a time Set your 85 PRINT TAB 8 communication software to send a line wh
305. turn but no line feed on the host display DATA expression expression R Specifies expressions to be retrieved by a READ statement DBY expression C R Retrieves or assigns a value at expression in internal data memory DIM array name size array name size C R Reserves storage for an array Default size is 11 0 10 Size limits are 0 254 Example DIM B 100 Reserves storage for 100 element array B 76 The Microcontroller Idea Book Programming DO program statements UNTIL relational expression R Executes all statements between DO and UNTIL until relational expression is true DO program statements WHILE relational expression R Executes all statements between DO and WHILE until relational expression is false END R Terminates program execution EXP expression C R Raises e 2 7182818 to the power of expression FOR counter variable start count expression C R TO end count expression STEP count increment expression program statements NEXT counter variable Executes all statements between FOR and NEXT the number of times specified by the counter and step expressions FPROG FPROG1 FPROG6 C Like PROG PROG1 PROG6 but using Intelligent programming algorithm FREE CR Returns the number of bytes of unused external data RAM GET R Contains the ASCII code of a character received from the host computer s key board After a program reads the value of GET For example G GET GET re
306. u found experimentally To add a second receiver build another circuit identical to Figure 12 2 s but with the address inputs set differently In this way you can transmit to a selected receiver by changing Al A5 at the transmitter Even if a receiver detects a transmission meant for another receiver it will ignore it since the address doesn t match Computer controlled Transmitter Figure 12 6 is a transmitter that is similar to 12 1 but with the manual controls replaced by outputs of an 82 C 55 PPI from Chapter 6 Port A and bits 4 7 of Port C are configured as outputs The two halves or 4 bit nibbles of the 8255 s Port A control the transmitted data and address The high nibble controls data inputs D6 D9 and the low nibble controls address inputs A1 A4 The fifth address input A5 is tied high so you can control both the data and address with one 8 bit port This reduces the number of decoders you can transmit to from 32 to 16 but this shouldn t be a problem in most applications 208 The Microcontroller Idea Book Wireless Links 82 C 55 MC145026 ANY CMOS 5V pag lo re AND GATE 15 iK PAI Zig PRATA Gan O 0 I iM MPS2907 P 4 Ax Tao 5V A 4 KHZ IN PA4 a paste i 38 2145 PAO To as PA7 6 p6 RED Myx A A 43K E D8 RTCH 1 5g P crel 22u i Te pst Ae 1 KHZ REMOTE CONTROL ENCODER Figure 12 6 Using an 8255
307. u can display the message HELP 134 The Microcontroller Idea Book Displays In Figure 8 5 s circuit an 82 C 55 controls the 7218C For complete control the circuit requires 10 outputs Bits 0 4 of Port A determine the data to be written including a decimal point controlled by ID7 If you don t need the decimal point tie pin 7 of the 7218C low Bits 5 7 of Port A select the digit to write to If you have four or fewer displays you can tie one or more of these lines low and free up another port bit Port C bit 4 controls WRITE The display mode input is tied high to select hexadecimal mode If you instead tie pin 9 to a port bit you can turn off the display by bringing the bit low To allow selecting different modes connect an additional output bit to the 7218D s MODE input Listing 8 3 uses the 7218D to display data using Figure 8 5 s circuit 7 segment LCDs An alternative to LEDs is liquid crystal displays LCDs Unlike LEDs which consume several milliamperes per segment LCDs are voltage controlled and require very little operating current Compared to LEDs LCDs are easy to read in bright light However because LCDs don t emit light as LEDs do but merely absorb or transmit it you need additional lighting to see them in the dark LCDs also tend to have narrower viewing angles than LEDs So whether to use LEDs or LCDs may depend on where and how you will use the display Most 7 segment LCD modules contain two or mor
308. u can use the 8052 BASIC to sense measure and control processes events or conditions Here are just a few examples of the uses you can put it to e data collection e machine control e test equipment e wired and wireless links for communications and control The Microcontroller Idea Book 1 Chapter 2 The 8052 BASIC is actually two products in one it s an 8052 microcontroller with the BASIC 52 programming language on chip To begin using the 8052 BASIC you need a minimum circuit consisting of the 8052 BASIC and some support components plus a personal computer This book contains specific instructions for use with IBM compatible or MS DOS computers but you can use any computer that has an RS 232 serial port and communications software to go with it Figure 2 1 shows the basic setup With an 8052 BASIC circuit connected by a serial link to a personal computer you have a complete development system with these abilities e You can write and run BASIC programs You use the keyboard video display and other resources of the personal computer to type and view the programs and commands that the 8052 BASIC system executes BASIC 52 is an interpreted language whose programs do not require an additional assembling or compiling step You can run programs or execute commands immediately after you write them e You can use BASIC 52 s programming functions to permanently store your programs in EPROM or other nonvolatile memory You
309. uage However Intel hasn t updated the program since version 1 1 Fortunately other programmers have taken on the task of improving and enhancing the language MDL Labs MDL BASIC is an EPROM that contains an enhanced version of BASIC 52 It includes new operators that set and clear individual bits in memory increment and decrement values and return the remainder in integer division MDL BASIC also has improvements for faster loading and running of programs and fixes many of BASIC 52 s bugs such as the problem with variable names beginning with F see Chapter 5 It requires a system that can operate with BASIC in external memory as described in Chapter 14 Other vendors including Blue Earth Research and Micromint have improved and added to the BASIC 52 interpreter as well The Microcontroller Idea Book 245 Chapter 15 BASIC compilers A BASIC compiler offers a middle ground between the BASIC 52 interpreter and assem bly language programming With a BASIC compiler you write your programs using the familiar keywords and syntax rules of BASIC but the compiled programs run on their own without requiring the BASIC 52 interpreter Binary Technology Systronix and Blue Earth are three vendors of BASIC compilers for the 8052 As with assembly language to use a BASIC compiler you first write a source file using any text editor But instead of using assembly language mnemonics you write the source file using the BASIC compiler s
310. uc tion or you can use the instruction that reads the HD44780 s busy flag at D7 to determine when the module is ready to accept a new instruction 144 The Microcontroller Idea Book Displays Interfacing Full control of an LCD module requires 8 bidirectional lines for reading and writing data and 3 outputs for the control signals To save four lines you can use the 4 bit data interface described later Also the ability to read the display and the busy flag at D7 are optional If you give these up you can use outputs such as the 74HC374 s instead of bidirectional port bits for DO D7 and eliminate one of the control lines by tying R W low Figure 8 9 shows an LCD module connected to an 82 C 55 using an 8 bit bidirectional interface The interface uses Port A and three bits of Port C on an 8255 You can use any of the 8255 s port bits if you write your program to match On the LCD module pins 1 3 connect to ground 5V and a contrast potentiometer For maximum contrast connect pin 3 directly to ground Pins 4 6 are the control signals for the LCD module These connect to three outputs on Port C The eight data bits pins 7 14 on the LCD module connect to Port A Listing 8 4 is a BASIC 52 program that initializes a 2 line display and writes LINE and LINE 2 to the matching lines Initializing the module On power up the LCD module must initialize properly If power up is clean with the supply voltage rising from 0 2V to
311. ues of expression s sequentially on BASIC 52 s argument stack PWM expressionl expression2 expression3 C R Outputs a pulse width modulated PWM sequence of pulses on pin 3 Expres sion is the width of each high pulse expressed in clock cycles Expression2 is the width of each low pulse expressed in clock cycles Expression3 is the number of PWM cycles output One clock cycle 12 XTAL One PWM cycle one high pulse plus one low pulse Expression and Expression2 must each be at least 25 Maximum for each Expression is 65535 RAM C Selects the current program in the RAM space 82 The Microcontroller Idea Book Programming RCAP2 CR Retrieves or assigns a value to the 8052 s special function registers RCAP2H and RCAP2L READ variable variable R Retrieves the expressions in a DATA statement and assigns each expression to a variable REM CR Introduces a comment or remark BASIC 52 ignores all text after REM in a pro gram line RESTORE R Resets READ pointer to the first expression in the DATA statement RETI R Returns program control to the line number following the most recently executed ONEX1 or ONTIME statement RETURN R Returns program control to the line number following the most recently executed GOSUB statement RND CR Returns a pseudo random number between 0 and 1 inclusive ROM program number C Selects a program in the EPROM space beginning at 8000h Default program number is 1 RROM p
312. ure the frequency at pin 3 of U3 or pin 3 of U2A If you re using U3 adjust R8 as needed for a 40 kHz output You can also measure at pin 12 of U1 to verify that its oscillator is about 1 kilohertz To send a test transmission set A1 A5 identically at U1 and U4 and set D6 D9 to the values you want to transmit The schematics show the components set up to transmit the value 7000 to address 00001 Aim IRED1 so that it points to MOD1 s photodiode window To begin place the transmitter and receiver a few feet apart To transmit press S1 momentarily to pulse pin 14 of U1 low At U4 LEDS should flash to indicate that a valid transmission was received At D6 D9 LED4 should be on and LEDs 1 3 should be off to show that the value 7000 was received To change the data to be transmitted move one or more jumpers or switches at U1 s D6 D9 Press S1 and LEDs 1 4 should change to match With these circuits I was able to receive data from 12 feet away with only casual aligning of the transmitter and receiver If you weren t able to measure and adjust U3 s frequency you can do so now Jumper pin 12 of U1 to ground to cause the transmitter to continuously transmit With IRED1 aimed at MOD1 slowly adjust potentiometer R8 until LEDS lights continue to adjust until LEDS turns off and then return R8 to about the middle of the range where LEDS is on You can then keep the potentiometer or replace it with a single resistor that matches the value yo
313. ust one function it toggles pin 1 Port 1 bit 0 of the 8052 An ORG directive tells the assembler the address at which to begin loading the routine Listing 13 1 The Microcontroller Idea Book 221 Chapter 13 Listing 13 1 Source file for a simple program to test assembly language interfacing with BASIC 52 org 3000h location where program will load in RAM cpl pl o complement Port 1 bit 0 pin 1 ret return to BASIC 52 end specifies 3000h You can change the address to match whatever locations you have available in your system The program body s single instruction complements bit 0 of Port 1 changing it from high to low or low to high A ret instruction then returns control to BASIC 52 To create and test the routine do the following Use a text editor to create a file containing Listing 13 1 Use your assembler to assemble the file A typical command line looks like this A51 bittog asm L bittog lst O bittog hex The above command tells the assembler to create two files the listing file bittog st shown in Listing 13 2 and the object file bittog hex in Intel hex format shown in Listing 13 3 File Formats for Assembly language Routines This is a good time to look at Intel Hex and other file formats in greater detail Most EPROM programmers are able to program EPROMs directly from the files created by assemblers and compilers but the file must be in a format that the programmer recognizes Three L
314. way that an error can slip through is if the address transmits correctly both times and the data contains the same error twice in a row if a transmitted 0 shows up as a at the receiver for example The chances of this are small especially since the 40 kHz modulation adds another layer of rejection of unwanted signals The data at D6 D9 remains until it is replaced by new received data VT remains high until an error is detected or until there is no input for four data bit times 32 milliseconds at 1 kHz Figure 12 2 shows LEDs at D6 D9 and VT for monitoring these outputs during testing Current limiting resistors aren t required since U4 sources only about 5 milliamperes 206 The Microcontroller Idea Book Wireless Links through the LEDs If you prefer an audible indicator to announce a valid transmission you can replace LEDS with a piezoelectric buzzer Instead of the LEDs you can connect just about any digital inputs to D6 D9 Power supply Options Figures 12 1 and 12 2 show the transmitter and receiver powered at 5 volts Recommended supply voltages for U1 and U4 are 4 5 to 18V for U2 and US 2 to 6V for U3 2 to 15V and for MOD1 4 7 to 5 3V This means that usable supply voltages for the transmitter circuit are 4 5 to 6V and for the receiver circuit 4 7 to 5 3V Each circuit draws only a few milliamperes though the test LEDs add about 5 milliamperes each when on Any regulated 5 volt supply that can output 100 milli
315. world gt 26 end gt list 18 PRINT hello world 28 END READY gt run hello world READY gt E Figure 3 6 BASIC 52 s sign on message and a simple program using the Windows Terminal accessory for communications Procomm Plus for DOS and Microsoft Windows 3 1 s Terminal Accessory but other communications software should have similar features and abilities Turn on the host computer and run your communications software Configure the software for 8 data bits no parity and 1 stop bit The baud rate you select isn t critical since BASIC 52 automatically adjusts to what you are using To start use a rate of 9600 or less Don t enable any handshaking or flow control options such as XON XOFF or RTS CTS Select the appropriate serial or COM port if necessary If you re using an MS DOS IBM compatible computer you must find a COM port and interrupt request IRQ level that aren t being used by your modem mouse or another device Because COM1 and COM3 often share an IRQ level as do COM2 and COM4 you generally can t use COM and COM3 at the same time or COM2 and COM4 If you have an external modem you can unplug it and use its serial port In Procomm Plus use the line port setup menu ALT P to configure In the Windows Terminal use the Settings menu Cable together the serial ports of the host and target systems 36 The Microcontroller Idea Book Powering Up You re now ready to power up the target sys
316. xactly like static RAM except that they contain a lithium cell and backup circuits that retain the RAM s contents when the main power supply is removed The backup is 48 The Microcontroller Idea Book Saving Programs guaranteed for at least ten years Dallas also makes a product called the SmartSocket which consists of an IC socket with an embedded lithium cell and backup circuits To create a NVRAM you plug your own static RAM chip into the SmartSocket Eight kilobytes is a convenient size that will store many short BASIC 52 programs or fewer longer ones For an 8K NVRAM you can use a DS1225 NVRAM or a DS1213B or DS1213C SmartSocket with a 6264 or similar static RAM Figure 4 1 shows the pinouts The 1213B and 1213C SmartSockets differ only in that the 1213B will also accept a 24 pin 2K SRAM with pins 1 2 27 and 28 unused and the 1213C will also accept a 32K SRAM which has address inputs at pins 1 and 26 The DS1225 offers a choice of two write protect voltages On the AB version write protection is guaranteed when the power supply is less than 4 5V and write operations are allowed when the power supply is greater than 4 75V The SmartSockets use these same voltages On the AD and Y versions of the DS1225 write protection is guaranteed when the supply is less than 4 25V and write operations are allowed when the supply is greater than 4 5V Either type should work in a BASIC 52 system with a regulated 5V supply Access times
317. xtra steps clear R W set RS write 5h to D4 D7 bring E high then low write OAh to D4 D7 bring E high then low Custom Characters If the 192 characters provided in the CG ROM aren t enough you can create your own To design a character draw a 5 x 7 matrix and fill it with 1s where you want dots and Os where you want nothing Figure 8 10 illustrates with an example of an upside down question mark for Spanish language messages Listing 8 6 creates the character and stores and displays it The Microcontroller Idea Book 151 Chapter 8 CUSTOM DOT BIT HEX ROW CHARACTER PATTERN VALUES VALUES E 00100 04 dogo 00000 QO l E 00100 04 2 E 01000 08 2 BOUOU 10000 10 4 E a 10001 11 5 EEEL 1110 QE 6 OOOOO 00000 00 7 Figure 8 10 You can create custom characters with the HD44780 controller The CG RAM stores the bit values for each row in the character For your own designs change the values of R1 R8 in lines 401 408 to match the symbol you want Mounting Displays in an Enclosure Mounting a display in an enclosure for a finished project usually involves cutting or drilling the enclosure and wiring the display to the control circuits For individual LEDs you can buy inexpensive mounting rings and drill matching holes in the enclosure s front panel Seven segment modules often mount on separate circuit boards that fit over an opening cut
318. y Oscillator alternatives ve included a choice of two designs for the 40 kHz oscillator One has a stable accurate output but requires a special timing crystal while the other uses more common components but requires a constant power supply voltage and accurate resistor and capacitor values for best stability and accuracy You can choose whichever you prefer and connect the output to pin 5 of U2 The crystal controlled oscillator uses a 40 kHz quartz crystal and an HCT132 Schmitt trig ger NAND gate U2A operated as an amplifier If you substitute a different inverter you The Microcontroller Idea Book 203 Chapter 12 may have to experiment with different component values Some combinations might cause the oscillator to run at harmonics of two or more times the crystal frequency Digi Key is one source for the sometimes hard to find 40 kHz crystals A ceramic resonator is another option for a 40 kHz source The other option is U3 which is a TLC555 timer configured as a 40 kHz oscillator Components R7 R8 and C5 determine the output frequency according to the formula shown For accuracy and stability use 5 or 1 tolerance values for these components The timing error of the 555 can also add a few percent error to the output frequency For best accuracy use a CMOS timer like the TLC555 rather than the bipolar 555 For an adjustable frequency substitute a 50K potentiometer for R8 Connect the center tap and one other lead of t
319. y depends on the kinds of information you want to show For simple status indicators discrete LEDs will do the job For numbers you can use 7 segment displays And if you need to display text or other symbols in addition to numbers character based LCD modules are a good solution This chapter will show how to use each of these in an 8052 BASIC system Using LEDs Discrete or individual LEDs light emitting diodes are an easy way to indicate status such as On Ready Mode selected and so on They are colorful eye catching and easy to interface to 5 volt logic Available colors now include blue as well as red green and yellow Some individual LED packages can emit red green or amber light depending on the voltages applied Like other diodes current passes through an LED in one direction only When a positive voltage is applied to the anode current flows and electrons migrate across an energy gap in the LED causing it to emit light The size of the energy gap determines the voltage drop across the LED as well as the color of light emitted A tinted case can also vary the color The Microcontroller Idea Book 125 Chapter 8 Table 8 1 The forward voltage drop across an LED varies with the color LED color typical forward voltage volts Red 1 6 Green 2 0 Yellow 2 0 Blue 3 2 Table 8 1 shows typical forward voltages for different colors of LEDs Typical LED operating currents are between 10 and 20 milliamperes For a bright
320. you power up an untested circuit it pays to be cautious I recommend the following steps First Steps Visually inspect the circuit You don t have to spend a lot of time on this but sometimes a missing or miswired wire or component or another problem will become obvious Install U1 U7 on the board making sure that pin 1 on each is oriented correctly Set J1 to BASIC and set J2 and J3 to match the size of your RAM at U7 With an ohmmeter measure the resistance from 5V to ground to be sure these aren t shorted together by mistake The exact value you measure isn t critical but if you read less than 100 ohms something is miswired and you need to find and fix the problem before you continue If you suspect a problem check the wiring of the power and ground connections comparing the connections to those on the schematic Be sure all components are oriented correctly When all checks out you re ready to boot up BASIC 52 Booting BASIC 52 For the initial check begin with everything powered down PII use the term host computer or host system to refer to the personal computer and target computer or target system to refer to the 8052 BASIC circuits Included are some specific tips for users of Datastorm s The Microcontroller Idea Book 35 Chapter 3 z 3 7 File Edit Settings Phone Transfers Help xMCS 51 tm BASIC U1 1 Em READY gt print mtop 8191 gt print xtal 11059200 gt 16 print hello
321. ypads Listing 7 3 Test program for Figure 7 9 s circuits 10 XBY 1F00H 49 REM 1 11 XBY 1F01H 50 REM 2 12 XBY 1F02H 51 REM 3 13 XBY 1F03H 67 REM C 14 XBY 1F04H 52 REM 4 15 XBY 1F05H 53 REM 5 16 XBY 1F06H 54 REM 6 17 XBY 1F07H 68 REM D 18 XBY 1F08H 55 REM 7 19 XBY 1F09H 56 REM 8 20 XBY 1FOAH 57 REM 9 21 XBY 1FOBH 69 REM E 22 XBY 1FOCH 65 REM A 23 XBY 1FODH 48 REM 0 24 XBY 1FOEH 66 REM B 25 XBY 1FOFH 70 REM F 30 DO 40 ONEX1 100 50 WHILE 1 1 60 END 100 KEY XBY 0E000H AND OFH 110 DAT XBY 1F00H KEY 120 PRINT CHR DAT 130 RETI requested function Chapter 8 describes how to add a small display to a system so you don t have to use the host computer s display for the menu For some projects you may want to use the numeric values of the keys directly rather than interpreting them as ASCII codes In this case you ll need to revise the lookup table or create a second table that matches the numeric values of the key legends with their data outputs For example a data output of O would correspond to 1 instead of 49 the ASCII code for 1 Again you usually can t use the keypad encoder s data outputs directly because they don t correspond to the values printed on the keys If an application requires that users enter multi digit numbers on the keypad your program will have to translate the individual digits into a single value Listing 7 4 is a program that
322. ystem requires additional components It must have external RAM in addition to the 8052 s internal RAM and most systems also have EPROM EEPROM or battery backed RAM for permanent storage of BASIC 52 programs Accessing this external memory uses all of Ports 0 and 2 plus bits 6 and 7 of Port 3 to hold data addresses and control signals for reading and writing to external memory Data here refers to a byte to be read or written and may be any type of information including program code The address defines the location in memory to be read or written During a memory access Port 0 s eight pins ADO AD7 first hold the lower byte of the address followed by the data to be read or written This method of carrying both addresses and data on the same signal lines is called a multiplexed address data bus It s a popular arrangement that many devices use since it requires fewer pins on the chip compared to giving each data and address line its own pin Port 2 s eight lines hold the higher byte of the address to be read or written to These lines make up the high address bus A8 A15 Together the 16 address lines can access 64 kilobytes 65 536 bytes of memory from 00000000 00000000 to 11111111 11111111 in binary or 0000h to FFFFh in hexadecimal Besides pins to hold the data and addresses the 8052 must also provide control signals to initiate the read and write operations Control signals include WR write RD read PSEN program sto

Download Pdf Manuals

Related Search

Related Contents

Philips LSBS3700 User's Manual  BU100XS 取扱説明書    Meade Instruments Polaris 130mm  Beyond WBYCM2 User's Manual  RCY21151W User`s manual  Whirlpool Series 810 User's Manual  PROJECTEUR DE DONNEES XJ-A130/XJ-A135 - Support  Bases de luz de transmissão TL RC™ TL RCI™  Ma thèse en 180 secondes Programme  

Copyright © All rights reserved. Failed to retrieve file