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Programming 8-bit PIC Microcontrollers in C 2008

1. A A V 2 71739 ion R3 VDD gt E 120R RXD R1 VSS o ___e _ R ae 620 MILFORD 2X16 BKP mi i U1 RA3 AN3 VREF T V 2 55838 RV4 U1 KO 13 33 J4 OSC1 CLKIN RBO INT 37 RV3 TJ OSC2 CLKOUT RB1 35 MCLR Vpp THV RB2 35 1k 2 RB3 PGM 37 5 RAO ANO RB4 3 z RA1 AN1 RB5 3o 1k RA2 AN2 VREF RB6 PGC 3 a l p RAS ANS VREF RB7 PGD gt RA4 TOCKI is RV1 oj K RA5 AN4 58 RCO T1OSO T1CKI R CA TIOSI CCP2 RV6 RV2 S REO ANS AD RC2 CCP1 H 72 REV ANG IWR RCS SCKISCL 18 1k RE2 AN7 CS RC4 SDI SDA lt ane RV RC5 SDO Se ik RC6 TX CK 5 ofk Ave RC7 RX DT S iko RDO PSPO 3 RD1 PSP1 57 ik RD2 PSP2 57 R2 RD3 PSP3 5 4k7 RD4 PSP4 55 ik Di RD5 PSP5 55 RD6 PSP6 5 RD7 PSP7 BZX79C2V7 hs PIC16F877 Figure 3 2 Input Voltage Measurement and Display combinations of analog and digital inputs are given in the 16F877A H header file Listing 2 19 When the program is compiled the define statement selected is replaced by the corresponding hex code which is then loaded into the ADC control register to set up the ADC The set of functions that control the ADC are listed in Table 3 1 The function setup_adc allows the clock rate ADC sampling rate to be selected to suit the applicatio
2. Listing 2 10 Continue Break and Goto Destination of goto Foreground operation Increments Port C Skip other tests if input 0 low Terminate loop if input 1 low Debounce inputs Restart at 100 C Programming Essentials 59 The goto again is triggered by the count reaching a set value which could be better achieved by using the While condition In a more complex program exiting a function in this way risks disrupting program control since the function is not properly terminated The significance of this should become clearer when functions are analyzed later If Else and Switch Case We have seen the basic if control option which allows a block to be executed or skipped conditionally The else option allows an alternate sequence to be executed when the if block is skipped We also need a multichoice selection which is provided by the switch case syntax This tests a variable value and provides a set of alternative sequences one of which is selected depending on the test result These options are illustrated in flowchart form in Figures 2 9 and 2 10 and the if else and switch case syntax is shown in Listing 2 11 The control statement switch variable tests the value of the variable used to select the option block The keyword case n is used to specify the value for each option Note that each option block must be terminated with break which causes the remaining blocks to be s
3. RO Simulate overcurrent AMPLIFIER X10 USA R100 McP5022 JUMPER VCF6D22 R16 38 LATCH Cear Lo R17 1k COMPARATOR OVERCURRENT OVERCURRENT SENSE CIRCUIT Figure 4 14 PICDEM Mechatronics Board Simulation Schematic OPTO C Mechatronics Applications 173 Circuit Description The central component of the PICDEM mechatronics board is the PIC 16F917 whose main distinguishing feature is the integral LCD drive facility The 3 5 digit LCD outputs occupy a large proportion of the available I O pins leaving a limited number for the other peripherals The digit segments are enabled by appropriate combinations of the segment and common inputs see Section 4 2 for details These are defined in an include file which must be added to the application project Three bias voltages are also required by the LCD at Vc 2V 3 and V 3 these are generated by a simple resistive divider The push button tactile switch inputs on the hardware are represented by toggle switches so that they can be left in the closed position if necessary when running the simulation They can be replaced with buttons if preferred A bank of active high LEDs are provided for output monitoring The temperature and light sensors are modeled as generic devices with user control of the set variable They normally are connected to an analog input on the MCU eit
4. This Loop is executed oo cca ee ees count 0 do output_C outbyte2 outbyte2 count while count 0 while 1 Break Continue and Goto It may sometimes be necessary to break the execution of a loop or block in the middle of its sequence Figure 2 8 The block must be exited in an orderly way and it is useful to have the option of restarting the block continue or proceeding to the next one break Occasionally an unconditional jump may be needed but this should be regarded as a last resort as it tends to threaten the program stability It is achieved by assigning a label to the jump destination and executing a goto label The use of these control statements is illustrated in Listing 2 10 The events that trigger break and continue are asynchronous independent of the program timing inputs from external switches which allows the counting loop to be quit or restarted at any time 58 Part 2 include use delay clock 4000000 again Labe Goto Statement Block Continue Break o Figure 2 8 Break Continue and Goto CONTINUE Continue C break 16F877A H main int outbyte outbyte 0 while 1 output_C outbyte delay_ms 10 outbytet if input PIN_DO continue if input PIN_D1 break delay_ms 100 if outbyte 100 goto again and goto jumps
5. setup_ccp1 ccp_pwm Select timer and mode set_pwml_duty 500 Set on time setup_timer_2 T2_DIV_BY_16 248 1 Clock rate amp output period while 1 Wait until reset The high output state called the duty cycle is expressed as a percentage of the overall period of the pulse wave A duty cycle of 50 gives an equal mark and space ratio Program PWM C Listing 3 4 shows the basic setup procedure The setup_ccp1 function selects the mode of operation of the CCP module The function setup_timer_2 controls the overall period of the PWM wave and has three arguments The first sets the timer prescale division ratio 16 in this case The prescaler is an additional counter stage that reduces the input clock rate by the selected ratio of 1 4 or 16 The second argument gives the overall output period from 1 to 255 times the input clock period The last value is the postscaler setting from 1 to 16 which divides the output from the MSB before it is fed to the interrupt system so that the interrupt period can be adjusted to be a multiple of the timer output The duty cycle is set via the set_pwm1_duty function call The value given is in the range 1 1023 an initial value for a 10 bit counter The value 500 gives a mark space ratio of about 50 The PWM wave is generated continuously after the setup is completed The values for duty cycle 500 and overall period 248 used in this example produce an output at
6. Analog X3 RS232 Figure 5 3 BASE Board Block Diagram reflected in real applications by the use of standard hardware such as PC compatible boards as the platform for a wide range of applications BASE Board A general purpose board with a typical selection of peripherals attached to a PIC 16F877A is described here This design was originally developed to demonstrate hardware interfacing techniques The PIC 16F877 BASE basic application and system evaluation board incorporates six analog inputs a 12 button keypad a parallel 16 X 2 character LCD 16k serial memory an RS232 port and ICD programming connections The block diagram is shown in Figure 5 3 the schematic in Figure 5 4 Here the board is used as a data logger It records input analog voltage levels at timed intervals and stores this data for later uploading to a host PC The PIC 16F877 has eight 10 bit analog inputs but to keep the demo system simple 8 bit conversion is used The reference voltage applied to RA3 is 2 56 V which gives a resolution of 2 56 256 10mV per bit and a precision of 100 256 0 4 The reference voltage and a test input occupy two of the analog inputs so six are available for connecting to an external target system Typically the inputs are connected to analog sensor inputs measuring temperature position strain and other physical variables from suitable sensors Another possibility is that the target system is an
7. ETUP_WDT or SETUP_COUNTERS see above RESTART_WDT Constants used for SETUP_WDT are define WDT_18MS 8 Watchdog timer interval 18ms define WDT_36MS 9 Watchdog timer interval 36ms define WDT_72MS 10 Watchdog timer interval 72ms define WDT_144MS TL Watchdog timer interval 144ms define WDT_288MS 12 Watchdog timer interval 288s define WDT_576MS 13 Watchdog timer interval 576ms define WDT_1152MS 14 Watchdog timer interval 1 15ms define WDT_2304MS 15 Watchdog timer interval 2 30s 1 11 11 1 1 1 1 1 1 11 11 1 1 1 1 1 11 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 _Timer1 Timer 1 Functions SETUP_TIMER_1 GET_TIMER1 SET_TIMER1 Constants used for SETUP_TIMER_1 are or via together constants from each group define T1_DISABLED 0 Switch off Timer 1 define T1_INTERNAL 0x85 Use instruction clock define T1_EXTERNAL 0x87 Use TICKI as clock input define T1_EXTERNAL SYNC 0x83 Synchronise TICKI input define T1_CLK_OUT 8 define T1_DIV_ByY_1 0 No prescale define T1_DIV_BY_2 0x10 Prescale divide by 2 define T1_DIV_ByYy_4 0x20 Prescale divide by 4 define T1_DIV_BY_8 0x30 Prescale divide by 8 1 1 1 1 111 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 11 1 1 1 1 _Timer 2 Timer 2 Functions SETUP_TIMER_2 GET_TIMER2 SET_TIMER2
8. output_D 0x20 Switch on Drive 3 delay_ms 200 Listing 4 9 Outline of Stepper Motor Speed Control Program STEPSPEED Specify MCU 16F917 Set default step delay time Main loop If Direction switch pulsed Call Forward If Direction switch pulsed Call Reverse Forward Call Speed Output one forward cycle 4 steps to motor Reverse Call Speed Output one reverse cycle 4 steps to motor Speed If Up button on halve step delay If Down button on double step delay 160 Part 4 Listing 4 10 Stepper Motor Speed Control Program STEPSPEED CMPB 22 4 07 TITIITTTTTT IITA TATA TTA TTT TATA TAA TTT Program for PICDEM Mechatronics Board stepper motor full step mode Connect RD7 P1 RD6 P2 RD5 P3 include 16F917 h use delay clock 8000000 void main int8 time 16 while 1 if input PIN_A3 delay_ms 10 if time 1 time time 2 while input PIN_A3 if input PIN_A4 delay_ms 10 if time 128 time time 2 while input PIN_A4 output_D 0x20 delay_ms time output_D 0x40 delay_ms time output_D 0x10 delay_ms time output_D 0x80 delay_ms time RD4 P4 plus all 6 jumpers for full bridge mode plus SW3 RA3 and SW4 RA4 Motor speed SW3 up SW4 down TIITITITTITI TAIT ITAA AI TAA TTA TATA ATT AAAI TAA TAT TL Variable step delay Loop always
9. RA4 TOCKI 15 _ RA5 AN4 55 RCO T10S0 T1CKI 12 3 RC1 T10Si CCP2 16 g REO ANS RD RC2 CCP1 12 Jo REV ANG WR RC3 SCK SCL e RE2 AN7 CS RC4 SDI SDA 5 RC5 SDO 5 RC6 TX CK gt a RC7 RX DT A Ee RDo PSPo 12 3 18 9 20 4 17 8 RD1 PSP1 21 5 16 7 RD2 PSP2 22 6 15 6 RD3 PSP3 27 7 14 5 RD4 PSP4 55 3 is gt RD5 PSP5 29 9 12 3 RD6 PSP6 55 To n 5 RD7 PSP7 PIC16F877 1 Figure 2 2 OUTBYTE Test Circuit with Output LEDs Program Analysis The main program contains just one statement output_D 255 This means output the number 2559 as a binary code to Port D of the chip setting all pins high obviously any number between 0 and 255 results in a corresponding output bit combination All statements are terminated with a semicolon This statement is a function call which means the compiler gets the machine code for this operation from the standard set of built in functions supplied with the compiler This particular function is one of a set of library functions of the form output_x n where x is the port number A E and n is the output value 0 255 The general form of the C function is function_name Any information needed by the function the function parameter s is inserted into the parentheses The main program starts with the key words void main and is enclosed between curly brackets or braces as they are officially known All program blocks are enclosed C Programming Essentials 39
10. The variable x is an 8 bit integer with whole number values 0 255 9 The value in binary can be seen when it is output at an 8 bit port Generally C integers int are stored as 16 bit values but C for 8 bit microcontrollers uses a default 8 bit integer format In Program VARL C an initial value is assigned to the variable 99 which is then used in the output function The point here is that the variable value can now be modified without having to change the output function call itself In the program an 8 bit variable x is declared and assigned a value 99 using the equals operator It is then output to Port D using the standard output function Looping Most real time applications need to execute continuously until the processor is turned off or reset Therefore the program generally jumps back at the end to repeat the main control loop In C this can be implemented as a while loop as in Listing 2 3 The condition for continuing to repeat the block between the while braces is contained in the parentheses following the while keyword The block is executed if the value or result of the expression in the parentheses is not zero In this case it is 1 which means the condition is always true and the loop repeats endlessly This program represents in simple form the general structure of embedded applications where an initialization phase is followed by an endless control loop Within the loop the value of x is incremented
11. outnum MPLAB IDE v7 52 Pia ESR View Project Cebugger Progammer Took Configre Window Hep OS ime SHwe dee MA SRRO TH cHHMaPOR co include 16F877A h void main aa outpat_D 255 U1 Ogia teesi port at ime 1 000us Boosh pont Reached PC A o E Message Proteus SM PICLEFS77A fa wo I barko Figure 2 3 MPLAB IDE Screenshot by braces allowing a multilevel hierarchical structure Main is a special function that contains the main program block within which all lower level functions are contained These can return a result to the calling function but the keyword void preceding the function name main means that this function returns no result since it is the top level function The preprocessor directive include 16F877A h instructs the compiler to include this processor specific file at the top of the program It contains labels for the registers in the selected MCU so that the compiler knows where to store MCU control variables Comments can be enclosed between slash star control characters or can follow a double slash in which case the comment is terminated with a line return The program header should contain as much information as possible to assist the user and facilitate future modifications Ideally line comments should describe the effect of the statement in the target system The meaning of the C program is independent of the layout on the page Only the seque
12. 1B int x while 1 t t output C x x delay_ s 10 wW i bad 2 rj e D ix a n in 4 o fe D be A G COP et OL Wi ital teva pt at ime 1 2471 Breakpoint Reached PC 0023 aa bard MPLAB IDE v7 50 Figure C 3 Virtual Oscilloscope Screenshot www newnespress com 226 Appendix C a full size version of the scope should appear when the simulation is run If not enable it in the Debug menu Adjust the controls to see the 50 Hz waveform displayed Figure C 3 shows the VSM analog scope and simulation clock display A breakpoint has been set at the if statement so the clock increments by 10 ms each time Run is selected ISIS also provides virtual signal sources meters voltage and current probes logic analyzer and counter timer as well as a graphing feature for analog and digital signals When the program is fully debugged it can be downloaded to hardware and retested This should leave only hardware faults to be rectified to obtain a working system Readers should note that Proteus VSM is continuously updated New features and components are added on a regular basis Specifically new MCUs are added as they are released by the manufacturers Version 6 was used to produce the simulation circuits in this book Version 7 has since been released which has for example an enhanced 4 channel virtual oscilloscope Visit www labcenter co uk for the latest product information C Compil
13. Wait 10ms End of main loop End of program 212 Appendix B a different set of features the number of ports memory size special input and output facilities and so on The include statement is defined as a compiler preprocessor directive by the leading hash symbol The include directive inserts the source code from the specified file as though it had been typed in Your own files can be included so you can make a library of your own routines for reuse as required Many built in functions are included by the compiler automatically for example output_C x Others have to be specified with use which identifies a library of functions used later in the program The directive uses delay clock 4000000 calls up the set of delay routines that need the MCU clock speed to be stated so that the correct delays can calculated The compiler manual indicates which functions need to be preceded by a use directive The initialization phase includes defining all global variables The variable labels such as x Or input_value are attached to the address where the variable value is to be stored The variable type declaration e g int allows the compiler to allocate an appropriate set of locations for the variable In CCS C the default integer size is 8 bits in others it is 16 Global variables remain in existence while the program is running and are recognized throughout all levels of the program However to save d
14. delay_ms 500 Delay 0 5s output_low PIN_DO Switch off LED The conditional sequence can also be selected by a while condition In Program WHILOOP C Listing 2 5 the input is tested in the loop condition statement and the output flashed on and off while the switch is open input high If the switch is closed the flash loop is not executed and the LED is switched off The program also demonstrates the delay function If this were absent the loop would execute in just a few microseconds since each machine code instruction takes 4 1s at a clock rate of 1 MHz The flashing of the output would be invisible The delay required in milliseconds is given as the function parameter and a reference to the function library is provided at the start of the program with the use directive This allows the compiler to find the library routine delay_ms The clock speed of the target processor must be given in the use directive so that the correct delay is calculated within the function Compare the syntax of the I O statements The function output_high PIN_nn is an output operation to set the port pin high The function input PIN_nn is an input function that returns a 1 or 0 from the input pin which can be tested by an IF or WHILE statement The ports are initialized automatically within these functions C Programming Essentials 45 Listing 2 6 FOR Loop FORLOOP C Repeat loop a set number of t
15. 30 31 asm 32 33 Start 34 BSF 8 0 006B 1283 BCF 0x3 0x5 006C 1408 BSF 0x8 0 353 BCF 8 0 006D 1008 BCF 0x8 0 36 GOTO Start 006E 286C GOTO 0x6c 37 38 endasm Fle Cat Vew Project Debugger Progammer Tods Configure Window Help Ocu SSB SAWP ReesevroscRBO t Bh SB MPLAB DE Editor ISR switches off output an int output_low PIN_DO delay_ms 100 while input PIN_BO Main block initialises int void main enable_interrupts int_ext enable interrupts global ext_int_edge L_TO_H Assembler block outputs fasan Start BSF 8 0 BCF 8 0 GOTO Start Figure 2 15 Debug Screenshot of FAST C Showing Output Frequency PIC Assembly Language A complete introduction to programming PIC microcontrollers in assembly language is given in PIC Microcontrollers An Introduction to Microelectronics by the author Elsevier second edition 2004 A brief overview is given here for those readers interested primarily in C programming To program in assembler some knowledge of the internal hardware of the MCU is needed The PIC16F877A architecture was www newnespress com C Programming Essentials 93 introduced in Part 1 of this book and the file register set is detailed further in Appendix C The primary purpose of any programming language is to get data into a system process it and output it in some useful form In assembly language the program statements act directly
16. 375 266 Answers 12 13 14 15 16 17 18 19 Sink Pg Ng M N F Source Pg Ng P M IN F P M F P F M N M P1 and N2 P2 and N1 M1 and M2 The current flows diagonally across the bridge so P1 and N2 are on together for forward current and P2 and N1 for reverse M1 switches on and off N2 and M2 switches N2 for PWM control With the inputs linked for full bridge operation P1 and P2 operate Drives 1 and 2 respectively which are connected to stepper motor Coil 1 brown and orange wires PWM1 is connected to CCP1 output P3 and P4 operate Coil 2 red and yellow and PWM3 is connected to CCP2 Sequence Drive 1 4 2 3 It is voltage operated with a high input impedance so it is simple to interface and can be driven directly from a logic output The output on resistance is low and the off resistance is high Gain of amp 10 Sensing resistor 0 1 Q Test resistor 3 3 0 5 3 82 Total resistance 3 8 0 1 3 92 Amp input voltage 0 1 3 9 X 5 0 13 V Amp output voltage 0 13 X 10 1 3V The latch consists of cross coupled NOR gates such that only one output can be high at a time The drives are disabled when the fault output is low and the LED output is high The comparator output goes high when an overcurrent is detected forcing the fault output low and switching on the LED This state is held until the Reset button forces the LED output low and t
17. Constants used for SETUP_TIMER_2 are define T2_DISABLED 0 No prescale define T2_DIV_BY_1 4 Prescale divide by 2 define T2_DIV_ByYy_4 5 Prescale divide by 4 define T2_DIV_BY_16 6 Prescale divide by 16 82 Part 2 TITTITTTTTTIT TTT TATA TT ATT TTT TATA TT ATTA TTA TTT TTA TTT TT TIT COP CCP Functions SETUP_CCPx SET_PWMx_DUTY CCP Variables CCP_x CCP_x_LOW CCP_x_HIGH Constants used for SETUP_CCPx define define define define define define define define define define define define define CCP_OFF CCP_CAP1 CCP_CAP1 CCP_CAP1 CCP_CAPT TURE_FI TURE_RI CCP_COMPARE_SI CCP_COMPARE_CIl CG La TURE_DIV_4 TURE_DIV_16 ET_ON_MATCH LR_ON_MATCH CCP_COMPARE_INT CCP_COMPARE_R CCP_PWM ESET_TIMER CCP_PWM_PLUS_1 CCP_PWM_PLUS_2 CCP_PWM_PLUS_3 long CCP_1 byte CCP_1 byte CCP_1_LOW byte CCP_1_HIGH long CCP_2 byte CCP_2 byte CCP_2_ LOW byte CCP_2_ HIGH are 0 4 OxA OxB OxC Oxic Ox2c Ox3c 0x15 0x15 0x16 Ox1B Ox1B 0x1C id fell Disable CCPx Capture on falling edge of CCPx input pin Capture on rising edge of CCPx input pi Capture every 4 pulses of input Capture every 16 pulses of input CCPx output pin goes high when compare succeeds CCPx output pin goes low when com
18. ISIS Professional Animating Fle Vew Ede L ray Took Design Gash Source Debug Template System Hep OSS eR 6B Bz 4QQQQ oo RO TIBA R PC CPU Source Code Ui x CWC oors Popoare J a Ail 33 llcuinmumeeem BARI C MPB V1 0 Name Address Value Output binary count when button pressed rris_c 0x0020 0b00000000 LSB SOR Simulation version Winclude 16F677A h fuse delay clock 4000000 void main t int x 3 3 iiy H aii Hdl while 1 t output_C x xet delay_ms 10 5 bad a ki 8 ta a n wn 7 1a D be A 5 COP et OLE a eapon a ime 70 215 Broskpori Reached PC 02 start AEP SDEUB 55 bari ISIS Profess as bard MPLAB IDE v7 50 TeaoWae J hopend doc Mic Figure C 2 Program Simulation Screenshot The Breakpoint button is used to set and clear breakpoints in the code at the current cursor position Program execution is run at full speed until stopped at the breakpoint Additional breakpoint control options can be selected by right clicking on the source code window This source window menu also allows the display to be modified to show line numbers and program memory addresses The assembler code for each statement can be displayed by selecting Disassembly Note that several lines of assembler code are needed for each C statement this is the reason that the C program needs more memory The Set Font option is useful if displayi
19. PROGRAMMING 8 BIT PIC MICROCONTROLLERS n C with Interactive Hardware Simulation Foreword Embedded microcontrollers are everywhere today In the average household you will find them far beyond the obvious places like cell phones calculators and MP3 players Hardly any new appliance arrives in the home without at least one controller and most likely there will be several one microcontroller for the user interface buttons and display another to control the motor and perhaps even an overall system manager This applies whether the appliance in question is a washing machine garage door opener curling iron or toothbrush If the product uses a rechargeable battery modern high density battery chemistries require intelligent chargers A decade ago there were significant barriers to learning how to use microcontrollers The cheapest programmer was about a hundred dollars and application development required both erasable windowed parts which cost about ten times the price of the one time programmable OTP version and a UV Eraser to erase the windowed part Debugging tools were the realm of professionals alone Now most microcontrollers use Flash based program memory that is electrically erasable This means the device can be reprogrammed in the circuit no UV eraser required and no special packages needed for development The total cost to get started today is about twenty five dollars which buys a PICkit 2 Starter Kit providin
20. reference inputs 0x09 6 analog 2 digital I O OxOA 5 analog 1 reference input C Programming Essentials 85 define define define define define define define define ANO_AN1_AN4_AN5 VREF_VREF ANO_AN1_AN4_VREF_VREF ANO_AN1_VREF_VREF ANO ANO_VREF_VREF Constants used in READ_ADC are ADC_START_AND_READ ADC_START_ONLY ADC_READ_ONLY 0x0B 0x0C 0x0D Ox0E Ox0F 1 6 4 anal log 2 reference inputs 2 digital 3 anal log 2 reference inputs 3 digital 2 anal log 2 reference inputs 4 digital 1 anal 1 anal log 7 digital log 2 reference 5 digital This is the default if nothing is specified TITITTITITI TTT TIAA TATA TATA ATTA TIT ATATITI ATA T TT IITOINT Interrupt Functions Constants used in ENABLE_INTE EXT_INT_EDGI EXT_INT_EDGE E are RRUPTS DISABLE_INTERRUPTS define L_TO_H 0x40 Interrupt on rising edge of external input define H_TO_L 0 Interrupt on falling edge of external input Constants used in ENABLE DISABLE_INTERRUPTS are define GLOBAL Ox0BCO Identify all interrupts define INT_RTCC 0x0B20 Identify Timer0 overflow interrupt define INT_RB 0x0B08 Identify Port B change interrupt define INT_EXT 0x0B10 Identify RBO
21. 228 30 Microchip MPLAB ICD2 29 Microchip PICkit2 programmer 27 Microchip Inc 137 Microcontroller unit MCU 1 configuration 8 12 features 3 4 5 programs 35 Microcontrollers 196 7 198 types 8 Microsoft Windows 191 Mikroelektronika C 227 234 235 Motor drives 138 139 142 143 MPLAB 2 10 11 C project 23 4 ICD2 145 IDE screenshot 39 MPSIM 181 2 N National Semiconductor 196 Null terminated string 75 O Object Selector panel 205 Operating System OS 191 Oscillator start up timer 10 out function 62 64 outbyte c 25 outbyte cof 25 outbyte err 26 outbyte hex 25 outbyte lst 25 outbyte mcp 26 outbyte mcw 26 outbyte pjt 26 outbyte sym 26 OUTBYTE test circuit 38 OUTNUM COF 37 output_D 255 38 output_high PIN_nn 44 Overview window 206 P Parallel slave port PSP 121 3 248 functions 124 operation 16 Parameter error 225 PC operating system 191 2 PCLATH program counter latch high 215 Permanent magnet PM 157 Philips 196 PIC H 232 PIC 16F877 65 file registers 213 214 status register bit functions 215 PIC 16FXXX instruction set 90 1 93 4 PIC assembly language 92 4 PIC chips 7 8 PIC registers 212 15 PIC16 MCU configuration 8 12 clock options 9 configuration in C 11 12 options 9 11 microcontrollers 1 8 MCU features 3 4 5 PIC chips 7 8 program execution 3 5 RAM file registers 6 7 MPLAB projects 22 6 MPLAB C project 23 4 project files 25 6 peripherals 12 18 analog to
22. Data transfer speed may be crucial to optimum system performance so the parallel connection may be preferred in this case This is feasible as long as the physical distance between the controller and the motors is not too far For serial data transfer speed bits per second increases as we progress from UART through I C to SPI As well as being the fastest SPI is also relatively simple to implement It can operate in Multimaster mode but needs hardware slave selection IC needs only two wires and operates like a mini network so it may be more effective for larger systems However the software is more complex and carries a significant addressing overhead The UART is a simple way to link a single master and slave and allows greater link distance by use of line drivers On the other hand it does not support any form of multiprocessor or bus system C Peripheral Interfaces 125 Table 3 10 Comparison of PIC Communication Ports UART SPI PC PSP Description Serial RS232 Host terminal single link Serial data bus connection with hardware selection Serial data and address bus connection with software addressing Parallel 8 bits bus connection with hardware control Clock Asynchronous Synchronous max Synchronous max Synchronous 5S MHz 5S MHz Wiring TX RX GND SCK SDI SS SCL SDA 10 k PSPO PSP7 RD pull ups WR CS Data 6 9 bits 8 bits serial 8 bits address 8 bits par
23. Or with the above with a number 0 15 reference voltage selection within range define VREF_A2 0x40 Le ADC ADC Functions SETUP_ADC SET_ADC_CHANNEL Constants used for SETUP_ADC are define ADC_OFF define ADC_CLOCK_DIV_2 define ADC_CLOCK_DIV_4 define ADC_CLOCK_DIV_8 define ADC_CLOCK_DIV_16 define ADC_CLOCK_DIV_32 define ADC_CLOCK_DIV_64 define ADC_CLOCK_INTERNAL define NO_ANALOGS define ALL_ANALOG define ANO_AN1_AN2_ AN4_ AN5 0 0x10000 0x4000 0x0040 0x4040 0x0080 0x4080 0x00c0 Constants used in SETUP_ADC_PORTS SETUP_ADC_PORTS aka SETUP_PORT_A READ_ADC Fosc MCU clock frequency ADC Off ADC clock Fosc 2 ADC clock Fosc 4 ADC clock Fosc 8 ADC clock Fosc 16 ADC clock Fosc 32 ADC clock Fosc 64 Internal 2 6us clock are 7 None all pins are digital I O 0 AO Al A2 A3 A5 EO El E2 are analog AN6_AN7_VSS_VREF 1 7 analog 1 define ANO_AN1_AN2_ AN3_AN4 define ANO_AN1_AN2_ AN4 VSS VREF define ANO_AN1_AN3 define ANO_AN1_VSS_VREF define ANO_AN1_AN4_AN5_AN6 reference input 2 5 analog 3 digital I O 3 4 analogue 1 reference input 4 3 analog 5 digital I O 5 2 analog 1 reference input AN7_VREF_VREF 0x08 6 analog 2 define ANO_AN1_AN2_ AN3_AN4 AN5 define ANO_AN1_AN2_ AN4_AN5 VSS_VREF
24. Range of Integer Variables Name Type Minimum Maximum Range intl 1 bit 0 1 1 2 unsigned int8 8 bits 0 255 256 28 signed int8 8 bits 127 127 256 28 unsigned int16 16 bits 0 65535 65536 216 signed int16 16 bits 32767 32767 65536 2 6 unsigned int32 32 bits 0 4294967295 4294967296 2 signed int32 32 bits 2147483647 2147483647 4294967296 2 Integers We have seen the integer whole number variable in use In the 8 bit MCU the default type is an unsigned 8 bit number giving a range of values of 0 255 This obviously is inadequate for many purposes so 16 and 32 bit integer types are also needed see Table 2 2 The range of a number is determined by the number of different binary codes that can be represented If n is the number of bits 2 different codes are possible As 0 must be included the highest number is 2 Hence the 16 bit unsigned integer has the range 0 65535 2 1 and the 32 bit 0O 4294967295 2 1 There is also a 1 bit type for bit storage Signed Integers The signed integer uses the most significant bit MSB as the sign bit so the range is accordingly reduced by half MSB 0 represents a positive number MSB 1 indicates a negative number Therefore the range for a 16 bit signed integer is 32767 to 32767 The sign bit must be processed separately to get the right answer from a calculation Floating Point Integers can re
25. S Salvo RTOS 232 Salvo RTOS User Manual 194 Search and sort 253 Sequence error 224 Serial LCD 65 8 69 Serial peripheral interface SPI bus 20 21 function set 116 serial port 247 test system 117 Index 277 set_ADC_channel n function 99 Set Font option 223 set_pwm1_duty function 110 set_up_adc_ports system function 99 setup_adc function 102 setup_adc_ports 102 setup_ccp1 function 110 setup_lcd function 151 setup_timer_1 156 setup_timer_2 function 110 setwave function 129 Signed integers 49 Simple program 35 6 Single analog input and display test circuit 100 SIREN program 45 7 SIREN C 45 Software design 180 181 199 200 and implementation 183 4 185 using CCS C 209 BARI list file 215 19 BARI source code 211 12 PIC registers 212 15 Special function registers SFRs 7 212 Special setup 255 SPICE model 206 Step Out Of 222 Step Over 222 STEPDIR C 158 Stepper motor connections 143 Stepper motor test 158 159 160 STEPSPEED 158 STEPTEST C 158 STMicroelectronics 196 strcpy function 75 String 74 Syntax error 224 System operation 182 3 System testing using Proteus VSM 221 errors 224 6 program attaching 221 222 program debugging 221 4 T TOCKI Timer0 clock input 109 Tagged Object edit buttons 207 Temperature control system 183 278 Index Temperature measurement 163 6 Terminal button 206 Test program 143 5 Test program debugging screen 146 Timer interrupt process 18
26. Software Design Using CCS C 211 BAR1 Source Code The program source code Listing B 2 starts with a comment block containing the name of the project author date version and program description Details of the compiler version development system and target hardware can be included In other words as much information as possible to allow the code to be modified updated and maintained effectively In CCS C the initialization phase includes a header file that defines the MCU for which the program is intended This is necessary as every PIC processor has Listing B 2 Source Code BAR1 C HEADER COMMENT SECTION kkkxkxkxkxkxkxkxkxkkxkkkkxkkkxkkkxkkkxkkkkxkkkxkkkkkxkxk BAR1 C MPB V1 0 Source code file details Output binary count Program description Simulation version Target system details INITIALIZATION SECTION kkkxkxkxkxkxkxkxkxkkxkxkxkkxkxkkxkkkxkkxkxkkkxkkkkkkkkkxkxxk include 16F877A h Define MCU regsisters etc use delay clock 4000000 Include delay routines void main Define main program block Start of main block int x Declare variable CONTROL LOOP SECTION KREKEKKKKEKKKKKK KKK KKK KR KKKKRKKKKKKKKKKKKKKKKK while 1 Define endless loop Start of main loop if input PIN_A4 Test input button Start of conditional block output_C x Output binary code X Increment output variable End of conditional block delay_ms 10
27. These are intended to provide a convenient reference source when developing CCS C programs in addition to the full CCS compiler reference manual Each part of the book is designed to be as self contained as possible so that parts can be skipped or studied in detail depending on the reader s previous knowledge and interests On the other hand the entire book should provide a coherent narrative leading to a solid grounding in C programming for embedded systems in general PIC Microcontroller Systems 1 1 PIC16 Microcontrollers e MCU features e Program execution e RAM file registers e Other PIC chips The microcontroller unit MCU is now big or rather small in electronics It is one of the most significant developments in the continuing miniaturization of electronic hardware Now even trivial products such as a musical birthday card or electronic price tag can include an MCU They are an important factor in the digitization of analog systems such as sound systems or television In addition they provide an essential component of larger systems such as automobiles robots and industrial systems There is no escape from microcontrollers so it is pretty useful to know how they work The computer or digital controller has three main elements input and output devices which communicate with the outside world a processor to make calculations and handle data operations and memory to store programs and data Figure 1 1 shows these in
28. rate how often the task will execute max time allowed for this task each time it is executed The microcontroller has all essential hardware resources built into one chip CPU program ROM data RAM and peripheral interfaces In a conventional microprocessor system these are provided as separate chips so that the system can be tailored to the application The system on a chip allows the microcontroller hardware to be configured for a specific application then manufactured on one chip giving the benefits of both the conventional microprocessor system and the microcontroller Familiarity cost complexity range development system availability features Sufficient I O pins peripheral support program memory size data memory size speed power consumption Answers 269 14 The prototype costs are mainly hardware and software design time As more 15 16 17 units are produced the development costs are shared so that the cost per unit falls with the volume of production see the figure Cost per Unit Volume The serial alphanumeric LCD needs only a single MCU pin and can display several lines of numbers and characters The 3 5 digit LCD is cheaper the digit display is larger and access is faster The size of the system and number of components largely determine the power consumption plus the current drawn by the MCU increases with the clock speed The component data sheets need to be consulted to predict
29. tested in real hardware by using the same MPLAB debugging tools used in the simulation mode source code display run stop step reset breakpoints and variable watch windows The target system needs its own power supply and an ICD connector With power supplied to the target load the application project files Select Debugger Select Tool MPLAB ICD2 The debug control panel appears with controls to run step and reset Figure 1 22 If the program is recomplied after a change in the source code the target can be automatically reprogrammed Use of breakpoints is generally the most useful debugging technique in C as it allows complete blocks of assembler to be executed at full speed These are enabled by right clicking on the source code and indicated by a red marker Once set they can be temporarily enabled and disabled The watch window selected from the View menu allows program variable values to be monitored as the program progresses 30 Part 1 ja test MPLAB IDE v7 52 Oc an GAw Pin ER View Project Debapam Progammer Tools Configue Window Heb Reese O sR DO F SSS o cuehere 0 X MCA Mec TEST C MPB 14 4 07 First program for testing PICDEM Mechatronics Board lashes 4 LEDs finclude 16F917 h fuse delay clock 8000000 void main i int n 0 while 1 t output_D n delay _ms 10 Figure 1 22 ICD Debugging Windows When debugging has been completed
30. which passes the required delay time to the delay function In this case the function code must be called up explicitly with the use delay clock 4000000 directive This tells the compiler to include the delay library functions allowing the system clock to be specified at the same time so that the correct delays can be calculated 62 Part 2 LEVEL 0 LEVEL 1 LEVEL 2 m void funl statements Main statements funl 4 statements statements gt void fun2 arg m an fun3 Seat statements statements statements fun2 arg lt fia gt statements return val Figure 2 11 Hierarchical C Program Structure Basic Functions A simple program using a function is shown in FUNCL C Listing 2 12 The main block is very short consisting of the function call out and a while statement which provides the wait state at the end of main In this case the variables are declared before the main block This makes them global in scope that is they are recognized throughout the whole program and within all function blocks The function out is also defined before main so that when it is called the function name is recognized The function starts with the keyword void which indicates that no value is returned by the function The significance of this is explained shortly The function itself simply increments Port C from 0 to 255 I
31. x The output 42 Part 2 Listing 2 3 Endless Loop Source code file ENDLESS C Program function Outputs variable count include 16F877A h void main int x Declare variable while 1 Loop endlessly output_D x Display value X Increment value therefore appears to count up in binary when executing When it reaches the maximum for an 8 bit count 11111111 255 it rolls over to 0 and starts again Decision Making The simplest way to illustrate basic decision making is to change an output depending on the state of an input A circuit for this is shown in Figure 2 4 INBIT DSN The switch generates an input at RCO and RDO provides the test output The common keyword for selection in many high level languages is IF Program IFIN C Listing 2 4 has the usual endless while loop but contains a statement to switch off Port D initially The input state is read within the loop using the bit read function input PIN_CO This assigns the input value 1 or 0 to the variable x The value is then tested in the if statement and the output set accordingly Note that the test uses a double equals to differentiate it from the assignment operator used in the previous statement The effect of the program is to switch on the output if the input is high The switch needs to be closed before running to see this effect The LED cannot be switched off again until the program is
32. x is 0 to 11 SFR addresses 110h 11Bh bank 1 These registers contain 12 X 8 96 bits which are identified individually bits 0 95 If one of these bits is high the corresponding LCD segment or pixel is on The LCD has a total of 26 numerical segments comprising three seven segment digits two segments for the MSD and three decimal points The MSD bits are controlled by the same bit as they always come on together giving only 25 bits actually required Therefore only some bits in the registers are used but the spare capacity allows more complex displays to be operated by the 917 in other applications We see that the bits that are used are not arranged very logically so they will be mapped by the LCD display function to simplify the output process The bits in the first three registers LCDDATAO LCDDATA2 are associated with COMO output the next three with COM1 and so on to COMS3 see Table 4 5 Unfortunately the C Mechatronics Applications 149 common inputs on the LCD are identified as COM1 COM4 so COM1 is controlled from the MCU output COMO and so on with COM4 being connected to COM3 MCU output pin The 16F917 MCU can provide up to 24 segment drive outputs SEGO SEG23 with four common connections COM0 COM3 These are used in defined combinations to control up to 24 X 4 96 segments or pixels in the display In this way 1 bit in the LCDDATAx registers controls one element of the display This dis
33. 10 points Write a basic program outline for the system described in Question 3 which has a single fixed operating temperature and no hysteresis A polling loop will wait for the start button to be operated while the stop button will shut down the system via the MCU reset input Explain briefly why analog inputs serial flash ROM and a serial data link are useful features of data logging system hardware Explain briefly how the use of a timer interrupt allows an accurate data logging interval to be more easily implemented than simple input polling Explain briefly the meaning of interrupt priority Compare briefly the different features of a standard PC operating system and an RTOS Explain briefly the significance of each part of the CCS C RTOS task definition directive task rate 500ms max 100ms Explain briefly the main difference between a microprocessor and microcontroller based hardware system PIC16 C Applications and Systems 201 11 Explain briefly the main advantage of a SoC when compared to a conventional microcontroller 12 State five criteria for selecting a microcontroller type or family 13 State five criteria for selecting a microcontroller for a given application 14 Explain briefly why the cost of a microcontroller application prototype is relatively high but the cost per unit reduces as more systems are produced using that design and sketch a curve that illustrates this fact 15 Compare briefly th
34. 1928 data Ports AE DCOP PSP IxTa PICTE Microcontroller 8kB code 3688 data Ports AC DOOP IxTiners PICTE Microcontroller 8B code 3686 data Ports AE DCOP PSP ITa PICTE Microcontroller 2kB code 1288 data Ports A C 1NCOP Timers PICTE Microcormnoller 4kB code 1928 data Ports AC DOOP IxTimers PICTE Microcorinoler 4kB code 1928 data Ports AE DOOP PSP ITa PIC16 Microcontroller 8B code 3666 data Ports A C DOOP 3xTieners PIC16 Microcontroller kB code 3688 data Ports AE DCOP PSP ITa PIC16 Microcorivoler 10248 code 2248 data 1288 EPROM Ports AB PICTE Microcontroller 2kB code 2248 data 1288 EPROM Ports A B Txt B td PICI6F877 MICRO LIB 23 June 2005 at 154923 Mactoprocesssor ICs PICT Famy Microchip PIC16 Microcortoller RB code 3598 data 2568 EPROM Pots AE 2CCP PSP IxTimers MSSP USART 10 bt ADC gt w 5 ir pi k 8 D tx n n Z a oo A 5 ee Oe E D MICRO PIC16 Microcortroller vath Comparatce USART SPI 12C Timers CCP 18 aa bart MPLAB Figure A 3 Picking the Microcontroller from the Parts Library The bar graph component is picked from the Optoelectronics category the crystal from Miscellaneous and the push button from the Switches and Relays The resistor and capacitor are the generic type ACTIVE components with an associated SPICE model must be used for interactive testing Not all components are active just a representative sel
35. 3 Less than lt if a lt 3 b b 2 Greater than or equal to gt if a gt 4 b b 1 Less than or equal to lt if a lt 5 b b 0 CCS C Programming Syntax Summary 241 Formatting Codes Code Displays sd Signed integer Su Unsigned integer SLu Long unsigned integer 16 or 32 bits SLs Long signed integer 16 or 32 bits SY Rounded decimal float use decimal formatting St Truncated decimal float use decimal formatting Se Exponential form of float Sw Unsigned integer with decimal point inserted use decimal formatting SX Hexadecimal SLX Long hex SC ASCII character corresponding to numerical value SS Character or string Arithmetic and Logic Operators 1 Operand Arithmetic 2 Operands Logic 2 Operands Assign value Add AND amp Increment Subtract OR Decrement Multiply XOR Complement Divide CCS C Program Function Reference This is a summary of the more commonly used functions available in CCS C Version 4 January 2007 For more details on how to use the listed functions and others not included here visit www ccsinfo com for a current manual download The following apply to all the following tables 1 2 All functions require a header file e g 16F877A H The numerous CAN and USB functions are not included since these interfaces are not typically available in 16 series MCU
36. 5 7 07 Outputs waveforms to DAC simulation file DAC DSN include 16F877A H include MATH H use delay clock 20000000 use fast_io D High speed output functions int n time 10 float step sinangle float stepangle 0 0174533 1 degree in radians int amp 91 Output instant voltage array ISR to read push buttons kkxkkxkxkxkxkxkxkxkkxkxkxkkxkkxkkxkkxkkxkkxkxkkkkkxkkxkkkkkkkxk int_rb void change if time 255 if input PIN_B4 time Increase period while input PIN_B4 if time 0 if input PIN_B5 time Decrease period while input PIN_B5 if input PIN_B6 reset_cpu Restart program if input PIN_B7 for n 0 n lt 91 n amp n 0 Zero output void setwave Arbitrary waveform values KKKKKKKKKK KKK KKK amp 0 00 amp 1 00 amp 2 00 amp 3 00 amp 4 00 amp 5 00 amp 6 00 amp 7 00 amp 8 00 amp 9 00 amp 10 10 amp 11 00 amp 12 00 amp 13 00 amp 14 00 amp 15 00 amp 16 00 amp 17 00 amp 18 00 amp 19 00 amp 20 20 amp 21 00 amp 22 00 amp 23 00 amp 24 00 amp 25 00 amp 26 00 amp 27 00 amp 28 00 amp 29 00 amp 30 30 amp 31 00 amp 32 00 amp 33 00 amp 34 00 amp 35 00 amp 36 00 amp 37 00 amp 38 00 amp 39 00 amp 40 40 amp 41 00 amp 42 00 amp 43 00 amp 44 00 amp 45 00 amp 46 00 amp 47 00 amp 48 00 amp 49 00 amp 50 50 amp 51 00 amp 52 00 amp 53 00 amp
37. 54 00 amp 55 00 amp 56 00 amp 57 00 amp 58 00 amp 59 00 amp 60 60 amp 61 00 amp 62 00 amp 63 00 amp 64 00 amp 65 00 amp 66 00 amp 67 00 amp 68 00 amp 69 00 C Peripheral Interfaces 131 amp 70 70 amp 71 00 amp 72 00 amp 73 00 amp 74 00 amp 75 00 amp 76 00 amp 77 00 amp 78 00 amp 79 00 amp 80 80 amp 81 00 amp 82 00 amp 83 00 amp 84 00 amp 85 00 amp 86 00 amp 87 00 amp 88 00 amp 89 00 amp 90 90 void main LEA Ekk kk kkk kkk kk kkk kkk kk kk kkk k k k kk kk k kk k k k k k kk k k KK enable_interrupts int_rb Port B interrupt for buttons enable_interrupts global ext_int_edge H_TO_L port_b_pullups 1 set_tris_D 0 Calculate waveform values kkkxkxkxkxkxkxkxkxkxkkxkkxkxkxkkkkxkxkkkkkkkxkxkkkxxkx k step 0 for n 0 n lt 91 n if input PIN_BO if input PIN_B1 amp n 100 Square wave offset Calculate sine values step stepangle s sinangle sin amp n floor sinangle 100 step step 1 if input PIN_B2 amp n n Triangular wave if input PIN_B3 setwave Arbitrary wave Output waveform vales kkkxkxkxkkxkxkxkxkxkkkkxkxkxkkkkxkxkkkkkxkxkxkkkkkkkkxkxk while 1 for n 0 n lt 91 n output_D 100 amp n delay_us time for n 89 n gt 0 n output_D 100 amp n delay_us time for n 0 n lt 91 n output_D 100 amp n delay_us time for n 89 n gt 0 n outpu
38. 8 Sign 0 positive Number 8 X 1 375 11 000000 a n 0x30 putc a n 5 0101 m 7 0111 a 6 0110 b 8 1000 c 5 0101 d 7 0111 e 2 0010 Continue means restart a loop Break means quit a loop Goto means jump to a label unconditionally switch x case 1 funl break case 2 fun2 break case 3 fun3 break Local variables are allocated memory only when a function is called and are discarded when the function has finished The memory can then be used for other purposes saving on overall memory requirements Functions are self contained blocks that implement a clearly defined set of operations receiving data for processing and returning results to the calling routine A structured program is a nested or hierarchical set of functions that 15 16 17 18 19 Answers 261 is easy to understand and modify Reusable function libraries can be created which save on programming time Compiler packages provide function libraries for the most common operations int variable type returned out name of the function int16 t variable and type received int16 n local variable declaration outbyte value returned from function The RS232 signal has a start bit 8 data bits and a stop bit The edge of the start bit triggers the LCD receiver shift register to sample the line in the middle of each data bit This is stored as an ASCII character and displayed Control c
39. An application developed on the PIC16F877A can easily be transferred to a smaller and cheaper midrange PICmicro The book also introduces the peripherals and shows how they can simplify the firmware by letting the hardware do the work MPLAB Microchip s Integrated Development Environment is also covered MPLAB includes an editor and a simulator and interfaces with many compilers including the CCS compiler used in this book Finally the book includes the Proteus simulator which allows complete system simulation saving time and money on prototype PCBs Dan Butler Principal Applications Engineer Microchip Technology Inc Preface This book is the third in a series including e PIC Microcontrollers An Introduction to Microelectronic Systems e Interfacing PIC Microcontrollers Embedded Design by Interactive Simulation e Programming 8 bit PIC Microcontrollers in C With Interactive Hardware Simulation It completes a set that introduces embedded application design using the Microchip PIC range from Microchip Technology Inc of Arizona This is the most popular microcontroller for education and training which is also rapidly gaining ground in the industrial and commercial sectors Interfacing PIC Microcontrollers and Programming PIC Microcontrollers present sample applications using the leading design and simulation software for microcontroller based circuits Proteus VSM from Labcenter Electronics Demo application files can
40. CCP1 of 250 Hz 4ms and a mark space ratio of 50 with a 4 MHz MCU clock The overall period is derived as follows Timer2 is driven from the instruction clock at 1 MHz Fosc 4 After prescaling the clock period is 16s and the timer counts up to 248 overflowing approximately every 16 X 248 3968 us or about 4 ms the figure 248 is used rather that 250 to adjust for software overheads in the timer processing The postscaler value is set to default 1 since the timer interrupt is not being used in this example C Peripheral Interfaces 111 Preload Set Interrupt CCPR1H CCPRIL Flag CCP1IF Set Clear Comparator Pin RC2 aS TMR1H TMR1iL nstruction Clock Figure 3 4 Compare Hardware Block Diagram The various setup options available for the timers and CCP modules are given in the 16F877 header file in Listing 2 19 Refer to the CCS User Manual for more details about using these options Compare Mode PWM uses the compare operation illustrated in Figure 3 4 to generate a timed output in conjunction with Timer2 The 16 bit CCPR register is preloaded with a set value which is continuously compared with the Timer1 count When the count matches the CCPR value the output pin toggles and a CCP interrupt is generated If this operation is repeated an interrupt and output change with a known period can be obtained Capture Mode This mode uses the timer in the inverse
41. CHECK SWITCHES Poll SW3 Debounce Not if min Wait switch Poll SW3 Debounce Not if max Wait switch 4 STEPS CLOCKWISE Step 1 Step 2 Step 3 Step 4 a procedure for modifying speed In the main loop the reversing button is tested by default the motor runs forward and is reversed each time the button is pressed Before each sequence of four steps the speed buttons are polled and the delay modified if requested The structure makes it easier to write the program with the right logical sequence A flaw C Mechatronics Applications 161 Listing 4 11 Stepper Motor Speed and Direction Control L11 1 1 111 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 11 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 11 1 1111 1111111 STEPDIR C PICDEM Mechatronics Board stepper motor speed and dirc Connect RD7 P1 RD6 P2 RD5 P3 RD4 P4 plus all 6 jumpers full bridge SW2 RA2 SW3 RA3 SW4 RA4 Motor speed SW3 up SW4 down motor dirc SW2 TISTTTSTTTITT TITTIES include 16F917 h use delay clock 8000000 int8 time 16 MCU select Internal clock Default speed PROCEDURES 0 11 11 1011171 0TTISTISTITTTTAT TTA TT void speed Halve or double speed if input PIN_A3 delay_ms 10 if time 1 time time 2 while input PIN_A3 if input PIN_A4 delay_ms 10 if time 128 time time 2 while input P
42. INT 3 47 RC2 CCP1 REO ANS RD 5 T OSC2 CLKOUT RBI 3s 18 RC3 SCK SCL RE1 AN6 WR iy MCLP Vpp THV RB2 35 534 RC4 SDI SDA RE2 AN7 CS 2 RAo ANO i ELD 25 RCO DICK 3 RB4 36 26 J RA1 AN1 RBS 35 28_ RC7 RX DT 5 RAZ AN2 VREF RBG PGC 5 ai w RA3 AN3VREF RB7 PGD 2 D 35 RDO PSPO RA4 TOCKI _ ig 6 54 RD1 PSP1 RA5 AN4 55 RCO T1OSO T1CKI E 21_ RD2 PSP2 A _ RCITIOSI CCP2 ED 2 RD3 PSP3 y RE0 AN5 RD RC2 CCP1 is 55 RD4 PSP4 Fo RE1 AN6 WR RC3 SCK SCL 38 4 T RD5 PSP5 T RE2 AN7 CS RC4 SDI SDA 2 29_ RD6 PSP6 RC5 SDO 54 22_ RD7 PSP7 ROG TX CK 5e RCRD PIC16F877 PROGRAM spitransmit cof RDO PSPO Slave Transmitter RD1 PSP1 5 gt RD2 PSP2 52 a PIC16F877 PROGRAM spireceive cot RD3 PSP3 2 Siaa pecs RD4 PSP4 53 ave Receiver RD5 PSP5 8 RD6 PSP6 e 3 RBO INT OSC1 CLKIN 3 RD7 PSP7 2 5E RBI osc2 cLkouUT HA 5g RB2 MCLR Vpp THV PIC16F877 37 RB9 PGM 2 32 RB4 RAO ANO lt PROGRAM spimaster cof 38 RBS RA1 AN4 3 CLOCK 4MHz 39 4 Jo RBG PGC RA2 AN2 VREF CFGWORD 0x673 4 2 RB7 PGD RA3 AN3 VREF 2 Master 15 RA4 TOCKI 2 RCOTIOSO TICKI RAS ANA SS 48_ RC1 T10SI CCP2 g 1 RC2 CCP1 REO ANS RD 5 18 RC3 SCK SCL RE1 AN6 WR iy 54 RC4 SDI SDA RE2 AN7 CS a 5 RCS SDO 67 RCBITXICK 28 RC7 RX DT E RDO PSPO 547 RD1 PSP1 ey RD2 PSP2 SPIC DSN 57 RD3 PSP3 Demonstrates SPI read 28 Ae atin from slave
43. MCU Alternatively provision is made for speed measurement using back emf where the drive is switched off for a short period in the cycle and the voltage generated by the motor measured The back emf is proportional to the speed while the motor is working as a tachogenerator The stepper motor has two sets of windings which are activated in sequence This moves the rotor one step at a time or 7 5 degrees The windings are connected to separate full bridge drivers consisting of half bridges 1 2 and 3 4 C Mechatronics Applications 141 Table 4 1 Mechatronics Board Fixed Connections Label Alt Func MCU Pin Function Dedicated I O SW1 MCLR RE3 1 Reset MCU if enabled in fuses ICSPDATA RB7 40 In circuit serial programming data ICSPCLK RB6 39 In circuit serial programming clock RX RC7 26 Receive data from RS232 interface TX RC6 25 Transmit data to RS232 interface Display I O SEGO RBO 33 LCD segment 0 see display map SEG1 RB1 34 LCD segment 1 see display map SEG2 RB2 35 LCD segment 2 see display map SEG3 RB3 36 LCD segment 3 see display map SEG6 RC3 18 LCD segment 6 see display map SEG21 REO 8 LCD segment 21 see display map SEG22 REL 9 LCD segment 22 see display map SEG23 RE2 10 LCD segment 23 see display map COMO RB4 37 LCD Common connection 0 COM1 RB5 38 LCD Common connection 1 COM2 RA2 4 LCD Common connection 2 COM3 RDO 19 LCD Common connection 3 VLCD1 RCO 15 LCD control voltage 1 Vaa
44. OXFFFF 65 535 connected to RCO T1CKI The count can be recorded at any chosen point in time alternatively an interrupt can be generated on overflow to notify the processor that the maximum count has been exceeded If the register is preloaded with a suitable value the interrupt occurs after a known count The counters are more frequently used as timers with the input derived from the MCU clock oscillator Since the clock period is accurately known the count represents an accurate timed period It can therefore be used to measure the period or frequency of an input signal or internal intervals or generate a regular interrupt Many PIC MCUs incorporate one or more Capture Compare and PWM CCP modules that use the timer registers A timer counter register may have a prescaler which divides the input frequency by a factor of 2 4 8 and so forth using additional stages or a postscaler which does the same at the output Timer0 has a prescaler that divides by up to 128 Timer has one that divides by 2 4 or 8 and Timer2 has a prescaler and postscaler that divide by up to 16 PWM Mode In Pulse Width Modulation mode a CCP module can be used to generate a timed output signal This provides an output pulse waveform with an adjustable high mark period 110 Part 3 Listing 3 4 Pulse Width Modulation Program Source Code PWM C MPB 11 4 07 Demo PWM output MCU clock 4MHz include 16F877A h void main
45. RRR k k k k k ERE REE k k k k k k k k k k k k k k k k k int vin0 Input variable setup_adc ADC_CLOCK_INTERNAL ADC clock setup_adc_ports ALL_ANALOG Input combination set_adc_channel 0 Select RAO LOM G delay_ms 500 vin0 read_adc Get input byte vin0 vin0 32 0x30 Convert to ASCII putc 254 putc 1 delay_ms 10 Clear screen printf Input putc vin0 Display input circuit The value of the zener load resistor has been selected by simulation to adjust the voltage to 2 560 0 1 A potentiometer is connected to each of the measured inputs so it can be set to an arbitrary test value The test program VOLTS C is provided in Listing 3 2 This time the ADC resolution is set to 10 bits to obtain a more precise reading Floating point array variables are declared for the input readings OQ 1023 and the calculated voltage The reference voltage 2 56 V is represented by the maximum conversion value 1024 so the scaling factor is 1024 2 56 400 bits per volt The input is therefore divided by this factor to obtain a display in volts Note that in the division operation both values must be float types The ADC port setup code selects all inputs as analog with RA3 an external reference although this is not obvious from the select statement format All the possible 102 Part 3 RV5 1 N
46. SDA 22 RC5 5DO 24 LCD1 RC6 TX CK gt RC7 RX DT 26 VDD TEMP 400 mviaeg G RDO PSPO g RXD 10k RD1 PSP1 57 RD2 PSP2 5 vss RD3 PSP3 22 RD4 PSP4 MILFORD 2X16 BKP RD5 PSP5 56 RD6 PSP6 5e RD7 PSP7 22 T PIC16F877 Ut Figure 5 2 Temperature Control System represented by the filament lamp output is switched on If it is above the set value a cooling fan switches on instead represented by the DC motor To avoid the outputs chattering at the switching point due to input noise switching hysteresis should be incorporated into the control sequence meaning that the switching level when the temperature is rising is higher than when the temperature is falling The temperature is displayed on the serial LCD as well as the status messages Heater ON or Fan ON The program structure ensures that the correct message is displayed during the changeover phase Software Design and Implementation The process of designing the software can be aided by writing a program outline The main structures and sequences are summarized using suitable layout and operational descriptions A typical problem to be overcome is that the displayed message must agree with the output status in the presence of hysteresis Therefore an output status flag variable type int1 is used to record the current output status This flag is then tested by the conditional output statement Note that the switching levels can be modified to s
47. The program simply switches on the drivers in the order 1 4 2 3 by outputting a suitable hex code to Port D The delay is set so that the steps can be counted visually It is helpful to attach an indicator flag to the motor shaft so that the stepping can be seen more easily The number of full steps per rev can then be confirmed 48 Program STEPSPEED Listings 4 9 and 4 10 is a development of the basic program to test the motor response to a range of step rates The input tactile switches change the speed by modifying the delay time parameter which is set to 16 ms by default This gives speed of 16 ms step 16 X 48 0 768 sec rev 0 768 X 60 46 rpm Direction Control The stepper motor program can now be further developed to include direction control as shown in STEPDIR C Listing 4 11 The program has been restructured to incorporate Listing 4 8 Stepper Motor Test Program STEPTEST C Test program for PICDEM Mechatronics Board stepper motor basic full step mode Connect RD7 P1 RD6 P2 RD5 P3 RD4 P4 plus all 6 jumpers for full bridge mode Motor moves 48 steps per rev 7 5 deg step ILALL TATA TAT AAAI TAA TAT AAAI TAA AI TAT AAAI TT include 16F917 h use delay clock 8000000 void main while 1 Loop always output_D 0x80 Switch on Drive 1 delay_ms 200 output_D 0x10 Switch on Drive 4 delay_ms 200 output_D 0x40 Switch on Drive 2 delay_ms 200
48. The registers and source variables may be inspected at each step When debugging C programs breakpoints are the most useful 182 Part 5 while stepping is more useful in assembly language The program sequence and variable values are monitored and errors identified when the results obtained do not agree with those expected Error information is provided principally in tabular form By comparison the Proteus VSM debugging environment has significant advantages The animated schematic gives a much more immediate indication of the overall program function Interactive input and output devices operate in real or simulated time The source code and breakpoints can be displayed In addition if the VSM viewer is run from within MPLAB the progress of the program can also be monitored simultaneously in MPSIM Therefore the more detailed debugging tools in MPSIM can be run alongside VSM and the most appropriate selected for any debugging task The simulated hardware design is thus tested in conjunction with the MCU firmware cosimulation allowing circuit modifications at an early stage and hardware software interaction to be studied on screen When the program is eventually downloaded to the real hardware it is now far more likely that it will work the first time The VSM Viewer is invoked from the debug tools menu in MPLAB and the program is attached and tested However if circuit modifications are needed VSM must be opened separately to r
49. U1 A 43 osc1 CLKIN RBO INT 22 777 OSC2 CLKOUT RBI e al7 al eer MCLR ver THV RB2 36 2 RB3 PGM 37 3 RAO ANO RB4 35 4 5 6 x 7 RA1 AN1 RB5 35 5 RA2 AN2VREF RB6 PGC o ala ae 3 RA3 AN3 VREF RB7 PGD gt RA4 TOCKI T Z RA5 AN4 55 RCO T10S0 T1CKI t gt gt ON RC1 T10Si CCP2 18 Ze 9 REO ANS AD RC2 CCP1 Hi See ee oe Fo REVANG WR RCS SCK SCL 38 2 RE2 AN7 CS RC4 SDI SDA 54 RC5 SDO ROG TX CK 5 gt RC7 RX DT 26 RDo PSPo 42 RD1 PSP1 57 RD2 PSP2 61 4 RD3 PSP3 5 4 RD4 PSP4 55 t RD5 PSP5 Se Pe RD6 PSP6 55 ji RD7 PSP7 VDD PIC16F877 RXD VSS MILFORD 2X16 BKP Figure 2 12 Calculator Schematic Listing 2 17 Calculator Program Source Code Filename CALC C Author Date Version MPB 21 12 07 Program Description Calculator demo program Hardware simulation CALC DSN KEKE KRKEKKKEK EKER EKER ER ERE RER KER RR ER EKER EK RE KEKE RRR ER ER ERE REE RKEEKERERERERE include 16F877A h use delay clock 4000000 use rs232 baud 9600 xmit PIN_D7 rcv PIN_D0O Declare variables KREKEKKKKKKE KKK KEK KKK KKK KK KK KKK KKK KK KKK KKKKKKKKEKKK KEKE int akey keynum opcode numofdigs start int32 numl num2 result reml rem2 rem3 rem4 int32 hunsdig tensdig onesdig int32 hunthous tenthous thous hunds tens ones C Programming Essentials 71 Declare functions kkxkkxkxkxkxkxkxkxkkxkxkxkxkxk
50. a host PC for uploading data acquired by the MCU subsystem Figure 1 10 The USART link can send data up to 100 meters by converting the signal to higher voltage levels typically 12V The digital signal is inverted and shifted to become bipolar symmetrical about OV line negative when inactive for transmission The PIC 16F877 has a dedicated hardware RS232 port but CCS C allows any pin to be set up as an RS232 port providing functions to generate the signals in software The basic form of the signal has 8 data bits and a stop and start bit The bit period is set by the baud rate A typical value is 9600 baud which is about 10k bits per second The bit period is then about 100 us about 1 byte per millisecond or 1 K byte per second 20 Part 1 The data are transferred between shift registers operating at the same bit rate the receiver has to be initialized to the same baud setting as the transmitter Assuming we are looking at TTL level data in the idle state the line is high When it goes low the receiver clock is started the data are sampled in the middle of each following data bit period and data are shifted into the receive register Figure 1 11 RS232 is used to access the standard serial LCD display in which case line drivers are not necessarily required ASCII characters and control codes are sent to operate the display which has its own MCU with a serial interface to receive and decode the data It then drives the pixe
51. analog board whose performance is being evaluated by measuring the circuit voltages under test conditions ICD Programming Connector Lo O R13 Reset 1k C3 OSC1 CLKIN RBO INT OSC2ICLKOUT RBI MCLR Vpp THV RB2 i ecec E RAQIANO req i RAMIAN1 RBS RA2 AN2 IVREF RB6 PGC RASIANSIVREF RB7 PGD RAAITOCKI_ RASIAN4ISS RCOMTIOSO MT1CKI o RC1 T10SI CCP2 REQ ANS RD RC2ICCPA RE1 AN6 WR RCSISCKISCL RE2IANTICS RC4 SDI SDA RC5ISDO RCGITXICK PIC16F877 RCTIRXIDT U1 ANALOG RDO PSPO INPRS a RD1 PSP1 5V RV1 RD2 PSP2 Reference RDSIRSPS voltage RD4IPSP4 ik RD5 PSP5 RD6 PSP8 RD7 PSP7 MAX232 7 um FPE J4 J5 ov RS232 LCD1 LMO16L 16F877A BASE MODULE MPB 2006 3 55 1 ji N 22u Figure 5 4 BASE Board Circuit Diagram R12 5V 180R A 24AA128 Serial Memory swiaysXs puv suoywryddy D 9LDId Z8L 188 Part 5 The measured values are stored in an I C serial flash memory chip which retains the data when powered down The driver routines for this device are demonstrated in section 3 6 The data can be transferred later to a host PC or other data terminal via the RS232 interface A driver chip is fitted to convert the data to line voltages The board has a simple keypad where operational parameters such as the sampling interval can be input during initialization or the mode of operation toggled between logging and uploading Scanning a keypad is described in s
52. analog inputs which are accessed via RAO RA1 RA2 RA3 RAS REO REI and RE2 being renamed ANO to AN7 in this mode All these pins default to analog operation but a combination of analog and digital inputs can be selected using the system function set_up_adc_ports These inputs are multiplexed into a single converter so they can be read only one at a time The function set_ADC_channel n selects the input channel The analog to digital converter module has a resolution of 10 bits giving a binary output of 0x000 to 0x3FF 1023 9 Therefore the measurement has a precision of 1 1024 X 100 which is slightly better than 0 1 This is good enough for most practical purposes A 16 bit integer or floating point variable is needed to receive this result 100 Part 3 A U1 g OSC1 CLKIN RBO INT 38 77 OSC2 CLKOUT RB1 56 Ry4 MCLR Vpp THV RB2 33 5 RB3 PGM 3 gt k 5 RAO ANO RB4 Se y RA1 AN1 RB5 39 1k RA2 AN2 VREF RB6 PGC 3y 3 RA3 AN3 VREF RB7 PGD lt 2 RAA TOCKL i 24 Rasan4SS RComTiOSo TICKI RC1 T10SI CCP2 16 34 REO ANS RD RC2 CCP1 Z Jo REVANGWR RC3 SCK SCL 38 2 RE2 AN7 CS RC4 SDI SDA S RC5 SDO ROG ITX CK 5 gt 4 LCD1 RC7 RX DT 2 amp i RDO PSPO 3 RXD RD1 PSP1 ee RD2 PSP2 EA RD3 PSP3 lt MILFORD 2X16 BKP RD4 PsP4t So RD5 PSP5 39 RD6 PSP6 30 RD7 PSP7 32 PIC16F877 Figure 3 1 Single Analog Input and Display T
53. and Local Variables Now assume that we wish to pass a value to the function for local use that is within the function The simplest way is to define it as a global variable which makes it available throughout the program In program FUNC2 C Listing 2 13 the variable count holding the delay count hence the delay time is global If there is no significant restriction on program memory global variables may be used However microcontrollers by definition have limited memory so it is desirable to use local variables whenever possible within the user functions This is because local variables exist only during function execution and the locations used for them are freed up on completion of function call This can be confirmed by watching the values of C program variables when the program is executed in simulation mode the local ones become undefined once the relevant function block is terminated If only global variables are used and the functions do not return results to the calling block they become procedures Program FUNC3 C Listing 2 14 shows how local 64 Part 2 Listing 2 13 Passing a Parameter to a Function FUNC2 C Uses global variables only TITTTTITITTTTTTI AIA TTT AT ATTA TTT ATA TIAA TATA AT ATA ATT include 16F877A H int8 outbyte 1 Declare global variables int16 n count void out 1 1 _ Function to run output count while outbyte 0 output_C outbyte outbyte
54. and a more sophisticated design is required to produce a waveform with a better resolution at higher frequencies It serves only to illustrate some relevant features of C and the principle of waveform synthesis that may be used in high performance digital signal processors such as the dsPIC range This is an application where critical sections of the code could be written in assembler for higher speed The main object of the program is to generate instantaneous voltages in sequence to produce a square sine triangular and arbitrary waveform The mid value for the output is 10040 Instant values ranging between 100 and 100 are added to this value to produce the output For the arbitrary pattern most values are 0 in this example with an increasing value at intervals of ten steps This produces a pulse modulated triangular waveform which might be used to test a digital filter but any other repetitive pattern can be entered as required The arbitrary sequence is generated from the values entered into the array amp n in the function setwave at the source code edit stage A mechanism for entering these externally in hardware could easily be added but that is rather tedious to demonstrate For the other waveforms the values are calculated The square wave is just a set of constant maximum 100 and minimum 100 values and the triangular wave is an 130 Part 3 Listing 3 13 Waveform Generator Source Code DACWAVE C MPB
55. be downloaded from the author s support Web site see later for details and run on screen so that the operation of each program can be studied in detail The purpose of this book is to e Introduce C programming specifically for microcontrollers in easy steps e Demonstrate the use of the Microchip MPLAB IDE for C projects e Provide a beginners guide to the CCS PCM C compiler for 16 series PICs e Explain how to use Proteus VSM to test C applications in simulated hardware e Describe applications for the Microchip PICDEM mechatronics board e Outline the principles of embedded system design and project development xiv Preface C is becoming the language of choice for embedded systems as memory capacity increases in microcontrollers Microchip supplies the 18 and 24 series chips specifically designed for C programming However C can be used in the less complex 16 series PIC as long as the applications are relatively simple and therefore do not exceed the more limited memory capacity The PIC 16F877A microcontroller is used as the reference device in this book as it contains a full range of peripherals and a reasonable memory capacity It was also used in the previous work on interfacing so there is continuity if the book series is taken as a complete course in PIC application development Microcontrollers are traditionally programmed in assembly language each type having its own syntax which translates directly into machine co
56. briefly why a PMOSFET and an NMOSFET are needed in each half bridge driver stage Outline how to set up the mechatronics board to control the speed of the DC motor in one direction only and state the required output from the MCU Study the setup for stepper motor driving in full bridge mode and by using the drive logic functions determine the winding activation sequence in terms of the current flow between drive terminals 1 2 3 and 4 C Mechatronics Applications 177 Assignments 4 To undertake these assignments install Microchip MPLAB www microchip com Labcenter ISIS Lite www proteuslite com and CCS C Lite www ccsinfo com Application files may be downloaded from www picmicros org uk Run the applications in MPLAB with Proteus VSM selected as the debug tool Display the animated schematic in VSM viewer with the application COF file attached to the MCU see the appendices for details Assignment 4 1 Download the mechatronics board simulation file PICDEMboard DSN and attach the program test cof Check that the simulation runs correctly causing the outputs at Port D to display a binary count Modify the delay count and confirm that the output timing changes accordingly Assignment 4 2 Download the PICDEM mechatronics board simulation file PICDEMdcmotor DSN and attach the program motorsim cof Check that it runs correctly displaying the motor revs completed on the display after the input switch has
57. current work because it is specifically designed for the PIC MCU supports the 16 series devices and has a comprehensive set of peripheral driver functions MPLAB C Project The primary function of the compiler is to take a source text file PROJNAME C and convert it to machine code PROJNAME HEX The hex file can then be downloaded to the PIC MCU The source file must be written in the correct form observing the conventions of both ANSI C and the specific compiler dialect The first program we see later in the tutorial section is shown in Listing 1 1 This can be typed into any text editor but we normally use the editor in MPLAB the standard Microchip development system software package This provides file management compiler interface and debugging facilities for PIC projects and may be downloaded free of charge from www microchip com Before starting work the complier also has to be installed The compiler file path is set in MPLAB by selecting Project Set Language Tool Locations The compiler can then be selected via the Project Select Language Tool Suite menu option Browse for the compiler executable file CCSC EXE and select it 24 Part 1 Listing 1 1 A Simple C Program OUTBYTE C MPB 2 1 07 V1 0 ia include 16F877A h MCU select void main Main block output_D 255 Switch on outputs A project folder called PROJNAME should now be created to hold the files that will be generated an
58. debugging tool such as Proteus VSM graphical output More details on simulation are provided in Appendix C and VSM interactive simulation is referred to throughout the text to provide circuit schematics and debugging facilities Programming A low cost programmer available at the time of writing is the Microchip PICkit2 programmer Figure 1 17 This connects to the USB port of the host PC with the programming module plugging direct into the target PCB The six way in circuit serial programming ICSP connector between the programmer module and the target board must be designed into the application circuit An in line row of pins provides the programmer connection to the target MCU as shown in Figure 1 18 Pin 1 carries the programming voltage 12 14 V and is connected to pin V which doubles as the MCU reset input MCLR Pin 4 PGD carries the program data and pin 5 PGC the program clock Any other circuits connected to these pins must be designed with care so that they do not interfere with the programmer The USB output provides the target board power up to a limit of 500 mA on pins 2 and 3 If necessary a separate target board supply must be provided 28 Part 1 Reset 10k MCU lt 1 o gt Vpp IMCLR _2 _ amp amp _ gt Vag lt 3 gt y lt 4 gt SS IicsP 3 PGD Interface PGC e Vdd Vss Board 5 V Supply Figure 1 18 ICSP Target Board Conn
59. directive to declare a function as an ISR here the compiler recognizes the keyword interrupt within the function name instead C Compiler Comparison 233 Listing D 3 Hi Tech C Sample Source Code Timer Interrupt include lt pic h gt Example code for using timerO on a 16F84 Sets up a 1 second interrupt and increments Port B Sef Calculate preload value for one second timer k KKKK TICK_PERIOD Li LE define PERIOD 1000000 define XTAI define IPERIOD define SCAI define TO_TICKS 256 define TICK PERIOD define RELOADS P 4000000 256 unsigned long seconds near char Service routine for timer 0 interrupt void interrupt timer0_isr void if reload R reload seconds PORTB reload TOIF 0 J main reload 0 O ELOADS 1 OPTION 0b0111 TOCS 0 TOIE 1 GIE 1 TRISB 0 for continue 4 1000000 XTAL SCALE IPERIOD ERIOD TO_TICKS if if Period in us one second here Crystal frequency 4MHz Period of instruction clock in us Timer 0 prescaler Number of counts for interrupt Period us of timer clock Calculate preload value Second count Reload count REEKKEEKKEKKEEKEKEKE KE Define function as timer ISR Set initial value of reload count Count seconds Change
60. existing company products and so on are significant Nevertheless the designer should keep an open mind as far as possible and needs to keep up with a rapidly developing technology in the embedded systems field to make the right choice not easy Microcontrollers A designer who has a store of expertise using a particular microcontroller type and development system will need a good reason to look elsewhere for a solution Gaining similar expertise in another system takes time and resources and any change must also take into account the future strategy of the company or design group The PIC family may be our first choice for the following reasons e Low cost e Simplicity e Good documentation e An established market e A development system provided e Third party support The PIC is well suited to the learning environment as it was originally pitched at the low end high volume low complexity market and is well supported by third party products Therefore the assumption implicit in this book is that the PIC is the best starting point even if the learner is later to progress to other processor types At the time of this writing the main alternatives are Atmel AVR Freescale Motorola STMicroelectronics Hitachi Philips and National Semiconductor PIC16 C Applications and Systems 197 We can approach hardware selection on the basis of the choice offered within the PIC range which was outlined in section 1 1 Some of the main fea
61. fgets spoint 01 string and stream identifier given CHECK SERIAL Check for serial input s kbhit Checks for serial input activity data but does not wait PRINT ERROR Write programmed assert a lt 3 Generates an error message if condition is FALSE CCS C Program Function Reference 247 Table F 5 SPI Serial Port spi Can Be Replaced by spi2 Function Description Example Comment SPI SETUP Initialize SPI serial port setup_spi spi_master See CCS manual for full list of options SPI READ Receives data byte from inbyte Waits for 8 bit data to SPI port spi_read arrive SPI WRITE Sends data byte via SPI spi_write Writes 8 bit data to port outbyte SPI serial line SPI TRANSFER Send and receive via SPI inbyte See CCS manual for spi_xfer variations outbyte SPI RECEIVED Check if SPI data received done spi_data_ Returns 0 for not is_in done 1 if done Table F 6 12C Serial Port USE I2C If Hardware Peripheral Fitted DEF INE for Software Interface Function Description Example Comment I C START Issue start command in i12c_start Start a data master mode transmission C WRITE Send a single byte i2c_write Send a data byte outbyte I C READ Read a received byte inbyte Read a data byte 12c_read I C STOP Issue a stop command in 12c_stop Stop the data master mode transm
62. generates eight chip select signals A memory space is created for the master where different peripherals are accessed at separate address ranges Table 3 9 summarizes the PSP functions Comparison of Communication Links We can now compare the available PIC MCU communication ports so that the most suitable can be selected for any given application Table 3 10 summarizes the main features 124 Part 3 Table 3 9 PSP Functions Operation Description Example PSP SETUP Enables or disables PSP setup_psp PSP_ENABLED PSP DIRECTION Sets the PSP data direction set_tris_e 0 PSP OUTPUT READY Checks if output byte is ready pspo psp_output_full to go PSP INPUT READY Checks if input byte is ready to pspi psp_input_full read PSP OVERFLOW Checks for data overwrite error pspv psp_overflow As we have seen three serial communication interfaces are available plus the parallel slave port In theory the parallel port should be the fastest because 8 bits can be transferred at a time The PSP can be used to create a multiprocessor system with a common data bus connected to same port on other MCUs with one master controlling the addressing system and selecting the slave MCU One example of such a multiprocessor system is a robot with a separate controller for each motor The master controller sends data to the motor slaves to set position speed or acceleration of that axis
63. in the STEPTEST Program to run the stepper motor at about 1 rev sec full step mode The temperature sensor on the mechatronics board has a calibrated output while the light sensor does not Explain why the comparator interface is therefore appropriate for light sensing but the ADC would be preferred for temperature measurement The temperature at the mechatronics board sensor is 25 C and is converted by the 10 bit ADC with a reference voltage of 2 048 V Calculate the ADC output value Write down logic functions for the Source Pg Ng and Sink Pg Ng conditions of the board driver logic in terms of the input variables P M N and F from the logic states shown in Table 4 8 List the hardware links required for the bidirectional DC motor drive in the mechatronics board and explain their significance in terms of switching the current in the bridge forward reverse and off State the connections required for the stepper motor drive in the mechatronics board and list the activation sequence required at the drive logic inputs State the features of the power MOSFET that make it suitable for use as a current driver device Refer to the simulation schematic Figure 4 14 and calculate the output voltage of the overcurrent amplifier in the mechatronics board simulation circuit when the test pot is set to its mid position Refer to the simulation schematic Figure 4 14 and explain briefly how the overcurrent latch functions Explain
64. in the range of 0 5 V In common with many sensors now available a signal conditioning amplifier is built in so that no additional components are needed to interface with an MCU Light Sensor The light sensor can be tested using the analog comparator inputs of the 16F917 which allow two input voltages to be compared An output bit in a status register is set if the positive input C is at a higher voltage than the negative input C or a reference voltage A range of setup options are defined in the header file The block diagram in Figure 4 11 shows the hardware configuration for this test The connector pin LIGHT the light sensor output is connected to RAO comparator input C and POT1 to RA3 comparator input C with LED D7 is assigned to RD7 to display the C Mechatronics Applications 163 POTI 0 5 V Cr LED DO Light Sensor Q 0 5V Figure 4 11 Comparator Test Setup Listing 4 12 Outline of Light Sensor Test Program LIGHTCON Select MCU 16F917 Initialize comparator input Main loop If light gt set level switch output OFF Else switch output ON comparator state When the light level is reduced the output switches on Conversely it goes off as the light is increased through the switching level which is adjustable using POT1 This simulates the operation of an automatic streetlight switch or security lamp The program LIGHTCON is outlined in Listing 4 12 and the source
65. interrupt the program is more efficient because time is not wasted in polling the ADC and the ADC result can be processed as soon as it is available 16 bit maximum count 65 536 remaining count 65 536 15 536 5 000 Instruction clock 8 4 2 MHz Clock period after prescale 16 2 8 Timer period 5000 x 8 40ms The Capture mode uses an input bit change to trigger the capture of the current timer reading transferring it into the preload registers for processing This mode can be used for input signal period measurement The Compare mode needs the preload registers to be loaded with a value with which the current timer value is continuously compared An interrupt flag is set and an output toggled when they match This mode can be used to generate an output of a given period See the figure 4 gt Overall Period a b T Duty Cycle d 1024 10 11 12 13 14 15 Answers 263 Output period 1000us 1000 clocks 250 X 4 timer count X prescale setup_timer_2 4 250 1 10 duty cycle 102 1023 set_PWM1_duty 102 The standard serial LCD is designed to receive 8 bit ASCII codes in RS232 format High speed is not required because only a limited amount of data is sent as the display is updated The longer link distance possible with RS232 may be useful if the display is mounted away from the MCU board 0x41 is the ASCII code for character A In the printf statement it is out
66. is open rather than closed System Testing Using Proteus VSM 225 Parameter Error If the wrong input is specified in the input statement e g PIN_A5 instead of PIN_A4 the button has no effect as the wrong input is being tested This error is detected by comparing the program and schematic Timing Error The delay time is calculated so that the LSB toggles every 10 ms If this figure is incorrect the output frequencies are wrong This can be checked by using the simulation clock or a virtual oscilloscope The simulation clock is displayed at the bottom of the schematic window To check the period of the output a breakpoint can be set at the beginning of the main loop The program then stops once per cycle and the time taken per cycle can be read from the clock A breakpoint is set by clicking on the Breakpoint button at the top of the source code widow The oscilloscope allows the output to be displayed in the time domain It is selected from the Virtual Instruments list Input A should be connected to the output RCO and E5 bart ISIS Professional Animating File Vew Edk Lirary Tods Design Gach Source Oetug Template System Hep DES ATED Bm 4QQQQ oo gt Ba TEMS R a gt PC CPU Source Code u1 s CAPIC BOOKSVAIC Progammingba i H R dis dak 38 oot BARI C NPB V1 0 Output binary count when button pressed LSB SOR Simulation version Sinclude 16F877A h 0004 fuse delay clock 4000000 void main
67. is the simplest way to generate a regular event in this case sampling at fixed intervals The 0 key is used to interrupt the logging process so it might be desirable to reassign the input from column 2 of the keypad to RBO the primary interrupt input Logging is restarted using the star key and data upload initiated using the hash key 5 4 PIC16 C Operating Systems e Polling e Interrupts e RTOS As microcontroller operating programs become more complex consideration must be given to the best method of organizing the program response to input memory management and output timing Three main methods are used to handle input and output events which after all is the primary requirement of a real time system In order of complexity they are I O polling interrupts and the real time operating system RTOS Polled I O This is the easiest and may be considered the default method of input and output where operations are simply scheduled as part of the main loop It is seen in most of the examples in this book because they have been deliberately kept simple The basic principle is illustrated in Figure 5 5 This option is fine if the delay that occurs between input signal and output response is not critical to the correct overall operation of the system The time taken to complete 190 Part 5 START Initialize m Read Input Process Input Write Ouput Figure 5 5 Polled I O
68. jo ueg o 36 PUSH BUTTON INPUTS 8 B A 40 u1 PICIBED17 Ne p od is ii gt Z RAC ANOICTISEG 2 ROO COMS coms ok L 3 RAVAN IC2 ISEG7 RD1 A PREN FOARE ta w comz 2 RAZIANZICZVREF ICOM2 Rowecr2 an Jeleje R51 ENABLES R8 S RAYANQICI NREFTISEGIS RD3 SEGIG SEGIO pring 04 64 UD anis 10k R6 JH RAA CIOUTITOCKISEGA RD4ISEGI7 tities 7 so R4 TEH RASANAC2OUT SSISEG5 RDSISEGIB Bene iT wok R2 14 eaciosc2icLKor1050 RDSISEGI9 ea elele 40k lt gt RAVOSCICLKITIOSI RD7 SEG20 SEG21 St REGANS SEGZ RoONLCDT pee vec Pa gt MCLR SEG22 Te REVANGISEG22 RCINLCD y lt vico2 SWZ SEG23 L4H REZJANTISEG23 Rcavicns pe VLCD3 PWMA sws MCLR P gt REIMCLR pp __ _REIISEGS E SEGS swa m Row GIspoIsrett Et SEGT Na swt 1k SEGO SE Racint seco ROS TICKIICCPVSEG1O PSE gt Swe SEGI St RBWSEGT RCGITXICKISCKISCLISEGY PSE wA Sw3 sec lt revise ROTIRA DTSDUSDAISEGE sw SEG3 lt S0_ rewsece R46 R49 te como lt f r RB4COMO 10k 10k fo com lt P Rasicom PIC a 6 So RBGICSPCLWICDCRISEGTA 6 RBZ ACSPDATACDDATISEG13 MCU aL LcD VOLT v _c03 MICROCHIP TM PICDEM MECHATRONICS BOARD MPB Ver 1 0 May 2007 Simulation of sensor and actuator circuits DC Motor control with incremental encoder feedback Stepper motor speed and position control Overcurrent protection circuit Temperature and light sensor measurement For test programs and full details see PROGRAMMING PIC MICROCONTROLLERS by Martin Bates 2007
69. manner to compare The CCP pin is set to input and monitored for a change of state When a rising or falling edge selectable is detected the timer register is cleared to 0 and starts counting at the internal clock rate When the next active edge is detected at the input the timer register value is copied to the CCP register The count therefore corresponds to the period of the input signal With a 1 MHz instruction clock the count is in microseconds An interrupt can also be generated on each active edge The general hardware configuration is shown in Figure 3 5 and a program to demonstrate this operation is shown in Listing 3 5 In the main block of Program PERIOD C Timer1 and the CCP mode are set up RE rising edge of signal to be captured The required interrupt is enabled and the program waits for the CCP1 interrupt indicating that the next rising edge has arrived The CCP 1 interrupt service routine clears the timer and interrupt ready for the next 112 Part 3 Set Interrupt Flag CCP1IF Prescale amp a CCPR1H CCPR1L Edge Select Capture Enable TMR1H TMRIL Instruction Clock Pulse Input Pin RC2 Figure 3 5 Capture Hardware Block Diagram Listing 3 5 Capture Mode Demo Program PERIOD C MPB 11 4 07 Demo of period measurement include 16F877A h RRR Rk kkk kk kk kk kkk ERE KEKE k kk k int_ccp1 Interrupt name void isr_ccp1 Interrupt fun
70. of flores fabs x Returns unsigned ABSOLUTE float positive value of signed float FLOAT Round a float upto roundup Returns integer from CEILING integer ceil afloat float FLOAT FLOOR Round a float down to integer roundown floor afloat Returns integer from float NTEGER Integer divide divres Returns a structure DIVIDE div numer d denom of quotient and remainder LONG DIVIDE Long integer divide lonres Returns a structure ldiv lnumer ldenom of quotient and remainder EXPONENTIAL Exponential function expres exp x Returns exp where x is a float continued 250 Appendix F Table F 11 continued Function Description Example Comment LOG BASE 10 Logarithm base 10 logres logl0 x Returns 10g10 x function where x is a float LOG BASE E Logarithm base e inres log x Returns 1n x where function x is a float DIVISION Modulus remainder modres Returns remainder of MODULUS of division fmod numer denom float division FRACTION Break up float into modfres Returns fractional MODULUS integer and fraction modf afloat amp whole part stores integer FRACTION Break up float into fexres Returns fractional part EXPAND integer and fraction frexp afloat amp whole BINARY Multiply a float by lexres Returns a float sint EXPAND integral power of 2 ldex
71. of pins can be used for this interface as the data rate is quite low allowing the signals to be generated in software However a dedicated hardware port is provided which must be used if an interrupt is needed The CCS C library functions associated with this port are listed in Table 3 6 The UART can be tested in simulation mode by connecting it to the virtual terminal provided in Proteus VSM as shown in Figure 3 7 The terminal input RXD receive data is connected to the PIC MCU TX transmit pin and the TXD transmit data output is connected to PIC MCU Rx receive It has additional handshaking transmission control lines RTS and CTS but these are not usually needed www newnespress com 114 Part 3 Table 3 6 RS232 Serial Port Functions Title Description Example RS232 SET BAUD RATE Set hardware RS232 setup_uart 19200 port baud rate RS232 SEND BYTE Write a character tothe putc 65 default port RS232 SEND SELECTED Write a character to s fputc A 01 selected port RS232 PRINT SERIAL Write a mixed message printf Answer 4 3d n RS232 PRINT SELECTED Write string to selected fprintf 01 Message serial port RS232 PRINT STRING Print a string and write sprintf astr Ans d n it to array RS232 RECEIVE BYTE Read a character to an n getc integer RS232 RECEIVE STRING Read an input string to gets spoint character array RS232 RECEI
72. on the stack so that the background task can be resumed when the ISR has finished Let us see how this can be applied to the motor controller assuming we are using a 16F877 MCU Figure 5 6 The input pulse period can be measured using one of the hardware timers Since Timer2 is designed to provide PWM mode Timer can be used to monitor PIC16 C Applications and Systems 191 o ISR START Co aS High Initialize Priority ae Task Background Task 4 Interrupt Return from Interrupt Figure 5 6 Basic Interrupt Operation the input working in Capture mode The counter timer register is fed from the system clock to measure absolute time intervals and the count is stored when the input changes The pulse period can then be worked out and this result compared with a target value which represents the required period hence speed If it is too long speed too low the motor speed is increased by increasing the PWM duty cycle in Timer2 If too short speed too high the duty cycle is reduced An interrupt is generated by Timerl when the count is captured the ISR modifies the output duty cycle as required and the controller then waits for the next interrupt to occur If the program uses multiple interrupts one ISR may be interrupted by another The interrupts may need to be assigned an order of priority so that a less important task does not interrupt a more important one W
73. other hand a major advantage is that a fully featured freeware version PICC Lite is available for hobbyists students and limited commercial purposes At the time of writing the following PIC MCUs are supported with no limitations as compared to the full version 12F629 12F675 and 16F84 A further set of 16 series chips can be used with a limitation on RAM and program memory 627 684 690 877 887 and 917 Other limitations are imposed due to the limited memory available in these chips Hi Tech also supplies Salvo RTOS including a freeware version This is a cooperative event driven priority based multitasking real time operating system designed for microcontrollers with limited RAM and ROM The manual supplied www pumpkininc com with this product contains a very useful introduction to RTOS principles and is recommended if further information is required on using RTOS in PICs An example of Hi Tech C source code is shown in Listing D 3 It outputs a binary count at Port B that is incremented every second using a timer interrupt The port register is addressed directly using the label PORTB The timer control bit labels are defined in the header file PIC H and set directly in the main routine Note that here the calculation of the initial loop count constant RELOADS is calculated in the initial directive block using the arithmetic and logic operations provided within the directive syntax Recall that CCS C uses a
74. port display Count down reloads Clear timer interrupt flag Initialise timer and wait for interrupt RREEKKKEKRKKEEEE prescale by 256 select internal clock enable timer interrupt enable global interrupts output changes on LED let interrupt do its job 234 Appendix D Figure D 1 Mikroelectronica EasyPIC4 Development Board Mikro C Mikroelectronica supplies range evaluation and development boards for the PIC and other microcontrollers as well as C Pascal and Basic compilers Figure D 1 The C compiler MikroC is well documented in a downloadable user manual and includes a good range of peripheral driver libraries including CAN Ethernet and graphical LCD drivers as part of a comprehensive I O library The packages are oriented toward the educational and hobby market offering additional features designed to assist the beginner in developing C applications An evaluation version does not appear to be available at the time of this writing and the compiler syntax can be assessed prior to purchase only by reference to code fragments given in the manual An ADC input block is reproduced as an example in Listing D 4 As we see the control registers are set up by loading control codes as hex numbers which requires the program designer to look up the necessary bit configurations However the ADC access function is simple and concise allowing the input channel to be selected as the function parameter Matrix C T
75. power consumption as this is not generally modeled in simulation systems A prototype must be built to confirm the power supply specification C is a higher level language than assembler so it is easier to learn and use as the meaning of the program statements is more obvious The same standard C syntax is used for all processors with the compiler converting the source code into the MCU specific assembly language This means that it is universal and to some extent portable between systems The basic programming techniques are applicable to all embedded systems with the main variation being in the I O function syntax 10 points bit 86 byte 86 define PIN_AO 40 86 define T INTERNAL 0x85 86 device ADC 8 directive 100 fuses 11 include 16F877A h statement 24 39 78 int_ext directive 107 list 86 nolist 86 pragma directive 230 task directive 193 use delay directive 66 78 212 use rs232 78 use rtos directive 193 7 Bit ASCII codes 53 16F877 peripheral interrupts 105 16F877 primary interrupts 105 877 chip 9 16 877 time registers 14 A ACTIVE components 206 ADO AD7 15 ALU arithmetic and logic unit 7 amp n array 131 Analog inputs 245 Analog setup 99 100 101 Analog to digital converter ADC 12 15 Animation options 224 ARES 203 Arithmetic and logical operations 54 241 Arrays 74 5 Assembler block 88 92 Index Assignment operations 52 4 55 Atmel AVR 196 B BARI 203 204 list
76. programming pins not be used for I O by the inexperienced designer as hardware contention could occur Electrically Erasable Programmable Read Only Memory Many PIC MCUs have a block of nonvolatile user memory where data can be stored during power down These data could for example be the secure code for an electronic lock or smart card reader The electrically erasable programmable read only memory EEPROM can be rewritten by individual location unlike flash program ROM The 877 has a block of 256 bytes which is a fairly typical value There is a special read write sequence to prevent accidental overwriting of the data Configuration in C The preprocessor directive fuses is used to set the configuration fuses in C programs for PICs A typical statement is fuses XT PUT NOWDT NOPROTECT NOBROWNOUT The options defined in the standard CCS C 16F877 header file are Clock Type Select LP XT HS RC Watchdog Timer Enable WDT NOWDT Power Up Timer Enable PUT NOPUT Program Code Protect PROTECT NOPROTECT In Circuit Debugging Enable DEBUG NODEBUG Brownout Reset Enable BROWNOUT NOBROWNOUT Low Voltage Program Enable LVP NOLVP EEPROM Write Protect CPD NOCPD Program Memory Write Protect WRT_50 WRT_25 with percentage protected WRT_5 NOWRT 12 Part 1 The default condition for the fuses if no such directive is included is equivalent to fuses RC WDT NOPUT BROWNOUT LVP NO
77. restarted Loop Control The program can be simplified by combining the input function with the condition statement as follows if input PIN_CO output_high PIN_DO C Programming Essentials 43 U1 B OSC1 CLKIN RBO INT ss eal OSC2 CLKOUT RBI 35 MCLR Vpe THV RB2 36 2 RB3 PGM 37 H 7 RA1 AN1 RB5 39 10k RA2 AN2VREF RB6 PGC 30 5 RA3 AN3 VREF RB7 PGD Ea RA4 TOCKI_ 15 RA5 AN4 SS RCO T10S0 T1CKI 1 3 RC1 T10Si CCP2 g REO AN5 RD RC2 CCP1 418 To RE1 AN6 WR RC3 SCK SCL g RE2 AN7 CS RC4 SDI SDA 5g RC5 SDO 55 RC6 TX CK 55 C RC7 RX DT gt D1 O RDO PSPO 1 ep o RD1 PSP1 57 220R RD2 PSP2 B LED RED RD3 PSP3 E RD4 PSP4 98 RD5 PSP5 59 RD6 PSP6 30 RD7 PSP7 PIC16F877 Figure 2 4 INBIT DSN Test Circuit with Input Switch Listing 2 4 IF Statement IFIN C Tests an input include 16F877A h void main int x Declare variable output_D 0 Clear all outputs while 1 Loop always x input PIN_CO Get input state if x 1 output_high PIN_DO Change output 44 Part 2 Listing 2 5 Conditional Loop WHILOOP C Input switch controls output flashing include 16F877A h use delay clock 1000000 MCU clock 1MHz void main while 1 while input PIN_CO Repeat while switch open output_high PIN_DO delay_ms 300 Delay 0 3s output_low PIN_DO
78. set of functions usually providing all the initialization and operating sequences required Example programs for analog input and the use of interrupts and timers are developed and the serial port functions demonstrated in sample applications The advantages of each type of serial bus are compared and examples showing the connection of external serial EEPROM for data storage and a digital to analog converter output are provided These applications can be tested in VSM but this is not essential use of VSM is optional throughout the book Part 4 focuses specifically on the PICDEM mechatronics board from Microchip This has been selected as the main demonstration application as it is relatively inexpensive and contains a range of features that allow the features of a typical mechatronics system to be examined input sensors temperature light and position and output actuators DC and stepper motor These are tested individually then the requirements of a temperature controller outlined Operation of the 3 5 digit seven segment LCD is explained in detail as this is not covered elsewhere A simulation version of the board is provided to aid further application design and implementation Part 5 outlines some principles of software and hardware design and provides some further examples A simple temperature controller provides an alternative design to that based on the mechatronics board and a data logger design is based on another standard hardwar
79. takes the execution point straight back to the set instruction giving a total loop time of C Programming Essentials 89 Listing 2 22 C Source Code with Assembler Block Source code file FAST C Author date version MPB 19 10 07 V1 0 Program function Demo of assembler block Simulation circuit ASSEM DSN KREKKEEKEKEKER ERE REE KEE EKER ERK ERR RE RE KEER ERR EKER ERKEREKEEEERKER KKK include 16F877A h use delay clock 4000000 ISR switches off output and waits for button exe int_ext void isrext output_low PIN_DO delay_ms 100 while input PIN_BO Main block initializes interrupt and waits for button void main enable_interrupts int_ext enable_interrupts global ext_int_edge L_TO_H Assembler block outputs high speed pulse wave asm Start BSF 8 0 BCF 8 0 GOTO Start endasm End of source code KREKKKKKKKKKKKKKKKKEKKKKKKKKK KKK KK KK four instructions or 441s The output therefore runs at 250 kHz 2 5 times faster than the C loop shown in Listing 2 20 If the MCU clock is uprated to the maximum 20 MHz the output frequency is 1 25 MHz A screenshot of this program FAST C under test in MPLAB with VSM debugging is shown in Figure 2 15 The frequency of the output is displayed on the VSM virtual counter timer instrument 90 Part 2 Table 2 11 PIC 16FXXX Instruction Set by Functional Groups Operation Exam
80. temperature is within specifications switch on RunOK indicator if temperature difference exceeds 5 C switch on flash fault indicator 2 Startup procedure e Power up the system reset the fault indicator e Display the set temperature on the LCD for operator adjustment e Wait for the start input push button 3 Overall operation e Switch on the first heater if the temperature is more than 2 C below the target e Switch on the other heater if the temperature is more than 5 C below the target e Run fans at a speed proportional to the positive temperature difference If the fan speed is zero switch on the fault indicator if the temperature sensor is out of range enable the fault mode e If the light level indicates direct sunlight add a positive offset to the fan speed in anticipation of an additional temperature rise If the light sensor is out of range enable the fault mode The block diagram Figure 4 13 shows the system I O requirements 168 Part 4 I O Allocation Once the inputs and outputs required have been established we can provisionally assign them to particular pins Table 4 7 as available in the PICDEM board The appropriate links can later be made for testing the application Implementation Output half bridge drivers 1 and 2 control the heaters In the final system these are interfaced via contactors if the load operates at high voltage For test purposes a 6 V filament lamp is connected to the driv
81. the chip must be reprogrammed for the final time by selecting Programmer Select Tool MPLAB ICD2 Then hit the Program Target Device button When done the program can be stopped and started using the Hold In Reset and Release From Reset buttons When the ICD pod is disconnected the program should auto run in the target system Design Package The components of the ECAD design package used in this book are listed below The PCB implementation tools are not described further as they are outside the scope of this programming guide e Circuit schematic capture Proteus ISIS e Interactive circuit simulation Proteus VSM e PCB layout design Proteus ARES e PIC development system Microchip MPLAB e PIC C Compiler Custom Computer Services CCS C e PIC programming and in circuit testing Microchip ICD2 www newnespress com PIC Microcontroller Systems 31 Assessment 1 5 points each total 100 1 2 3 4 10 11 12 13 14 List five consumer products that typically include a microcontroller Identify the five functional elements of a microcontroller Explain why flash ROM is an important technology in microcontrollers State five important characteristics of a microcontroller that should be considered when selecting the best part for a given application Describe briefly the process of program execution in a microcontroller referring to the role of the program memory instruction register program cou
82. the definitive block diagram in the data sheet Program Execution The chip has 8k 8096 X 14 bits of flash ROM program memory which has to be programmed via the serial programming pins PGM PGC and PGD The fixed length 4 Part 1 ar 40 lt RB7 PGD MCLR Vep gt 1 RAO ANO 4 gt 2 39 4 gt RB6 PGC RAI AN1 4 gt 3 38 gt RB5 RA2 AN2 VREF CVREF 4 gt T 4 37 RB4 RAS ANS VREF 4 gt 5 36 4 gt RB3 PGM RA4 TOCKI C1OUT 4 gt 6 35 gt RB2 RAS AN4 SS C20UT 4 gt 7 a 34 4 gt RB1 RE0 RD AN5 gt 8 Noo 33 O lt gt RBO INT REVWR ANG lt gt 9 3204 Vvo RE2 CS AN7 lt gt 10 S 31 lt Vss Voo 11 o 30 RD7 PSP7 Vss gt J 12 2 29 RD6 PSP6 OSC1 CLKI J 13 Oo 28 lt gt RD5 PSP5 OSC2 CLKO 4 Q14 27 RD4 PSP4 RCO T10SO T1CKI gt 15 26 gt RC7 RX DT RC1 T10SI CCP2 gt 16 25 RC6 TX CK RC2 CCP1 4 gt gt E 17 24 RC5 SDO RC3 SCK SCL 4 gt gt 18 23 RC4 SDI SDA RDO PSPO 19 22 RD3 PSP3 RD1 PSP1 lt gt 20 21 RD2 PSP2 Figure 1 2 16F877 Pin out reproduced by permission of Microchip Inc instructions contain both the operation code and operand immediate data register addres
83. the drives This fault condition also occurs on power up ensuring that the drives start only after the Clear Fault switch is pressed C Mechatronics Applications Table 4 4 Stepper Motor Connections Label Alt Func MCU Pin P1 RD7 Enable source current driver stage 1 PWM1 CCP1 Pulse width control driver stage 1 Enable sink current driver stage 1 Enable source current driver stage 2 Pulse width control driver stage 2 Enable sink current driver stage 2 Enable source current driver stage 3 Pulse width control driver stage 3 N3 RD5 Enable sink current driver stage 3 P4 RD5 Enable source current driver stage 4 PWM4 CCP2 Pulse width control driver stage 4 N4 RD4 Enable sink current driver stage 4 Vs Forward Reverse gt an gt FET FET 2 4 OV Figure 4 4 Full Bridge Driver Connection of the DC Motor Test Program An initial test program for the PICDEM board is used to check that the downloading and in circuit debugging modes are operational The system setup is shown in Figure 4 5 the test program outline in Listing 4 1 and the source code in Listing 4 2 The program outline can be used in more complex applications to help to construct the program 144 Part 4 ICD2 _____ J Download amp Debug PIC Program 16F917 LEDS PICDEM1 e D7 RD7 e D6 RD6 RD
84. to analog converter DAC 127 Disassembly Listing 145 DOWHILE C 56 57 DsPIC digital signal processor 8 Duty cycle 110 E E blocks 234 Electrically erasable programmable read only memory EEPROM 11 126 enable_interrupts global 108 enable_interrupts int_ext statement 108 Enumeration 77 Erasable programmable ROM EPROM 1 2 ext_int_edge H_TO_L 108 External interrupt test hardware 107 F FAST C 89 92 File select register FSR 214 Flash ROM 2 FLOAT C 67 8 69 Floating point FP 49 52 FOR loop 45 for statement 73 for 210 FORLOOP C 45 Formatting codes 66 68 241 Frames per Second settings 224 Freescale Motorola 196 FUNC1 C 62 63 function_name 38 G General purpose registers GPRs 7 212 General timer operation 14 get_timer1 156 getc function 114 Index 273 Global variable 63 4 65 Globals option 223 H Hardware design 179 80 197 9 using ISIS schematic capture 203 design specification 203 4 schematic circuit 204 5 schematic edit 205 7 Hardware selection 195 6 Header file 78 86 Hitachi 196 HiTech PIC C 227 230 3 Hold In Reset buttons 30 I T O allocation for temperature controller 168 T O functions 240 T O pin operation 13 PC serial port 247 i2c_start function 120 If else and switch case 59 60 61 if statement 42 163 226 219 IFIN C 42 43 In circuit programming and debugging ICPD 10 11 In circuit serial programming ICSP 27 INBIT DS
85. to be assigned explicitly In C the variable label is automatically assigned to the next available location or locations many variable types need more than 1 byte of memory The variable name and type must be declared at the start of the program block so that the compiler can allocate a corresponding set of locations Variable values are assumed to be in decimal by default so if a value is given in hexadecimal in the source code it must be written with the prefix 0x so that OxFF represents 255 for example A variable called x is used in the program in Listing 2 2 VARI C Longer labels are sometimes preferable such as output_value but spaces are not allowed Only alphanumeric characters a z A Z 0 9 and underscore instead of space can be used By default the CCS compiler is not case sensitive so a is the same as A even though the ASCII code is different A limited number of key words in C such as main and include must not be used as variable names C Programming Essentials 41 Listing 2 2 Variables Source code file VARI C Author date version MPB 11 7 07 V1 0 Program function Outputs an 8 bit variable Simulation circuit OUTBYTE DSN kkkh kk kkk kkk kk kk kkk kkk kkk kkk kkk kkk kkk kkk kkk kk kkk kkk kkk kkk kkk kkk include 16F877A h void main int x Declare variable and type x 99 Assign variable value output_D x Display the value in binary
86. to high impedance output_float DO Allows an external source to control the line SET PULLUPS Switch input pull ups on or off port_a_pullups TRUE Input floats to high value port A or B only SET DIRECTION Initialize port bits for input or output set_tris_a OxOF Explicitly sets up data direction register CCS C Program Function Reference 245 Table F 2 Analog Inputs Requires DEVICE ADC nn Function Description Example Comment SETUP Initialize ADC setup_adc ADC_CLOCK_ INTERNAL All modes listed in device header file PINS SETUP Initialize ADC pins setup_adc_ports RAO_ANALOG All modes listed in device header file CHANNEL SELECT Select ADC input set_adc_channel 0 Channels 0 7 selected via multiplexer READ Read analog input inval read_adc 8 bit read 0 255 10 bit read 0 1024 device option Table F 3 Timers Requires Chip Header File Only e g 16F877A H Function Description Example Comment TIMERX SETUP Set up the timer mode setup_timer0 RTCC_INTERNAL RTCC_DIV_8 Clock source and prescale ratio TIMERX READ Read a timer register 8 or 16 bits count0 get_timer0 Timer numbers 0 5 valid as fitted TIMERX WRITE Preload a timer register 8 or 16 bits set_timer0 126 Timer nu
87. transmitter 28 RD6 PSP6 and write to slave receiver RD7 PSP7 via master controller U3 Figure 3 8 SPI Test System Schematic 118 Part 3 Listing 3 7 SPI Slave Transmitter Source Code SPITRANSMIT C MPB 20 6 07 Serial I O using SPI synchronous link Simulation hardware SPIC DSN transmitter program attached to U2 include 16F877A h void main RRR kkkkkkkkkkkkkk kkk kkk kkk kkk kk kk kkk kkk kk int sendnum setup_spi spi_slave Set SPI slave mode while 1 sendnum input_D Get BCD input spi_write sendnum Send BCD code to master Listing 3 8 SPI Master Controller Source Code SPIMASTER C MPB 20 6 07 Serial I O using SPI synchronous link Simulation hardware SPIC DSN master program attach to U1 include 16F877A h void main L AA kkkk kkk kkk kk kk kk kkk kkk kk kk kk kkk k kkk kk k k kk k kk k k k k int number setup_spi spi_master Set SPI master mode while 1 number spi_read Read SPI input BCD code spi_write number Resend BCD code to slave 3 6 PIC16 C I C Serial Bus e PC simulation test system e C control address and data bytes The inter integrated circuit 1 C synchronous serial bus provides a means of exchanging data between peripheral devices and microcontrollers using software C Peripheral Interfaces 119 Listing 3 9 SPI Slave Receiver Source Code SPIRECEIVE C MPB 20 6
88. which case it does not run in real time This can be checked by observing the simulation clock display Typical Errors The types of errors that appear when the program is compiled are either syntax or linker errors A syntax error might be a spelling mistake in the source code or an undeclared variable Linker errors appear when the program files are combined to create the final program a common one is that the include files have not been placed in the project folder and cannot be found by the linker Logical errors on the other hand appear only when the program is tested and these are easier to correct if detected prior to downloading to hardware by using a simulator such as MPSIM or VSM VSM is easier to use as the errors are more readily spotted in the animated schematic than in the numerical output of MPSIM Some simple examples of possible errors in BIN1 C are outlined next Sequence Error While the increment statement follows the output statement the first output is 00000000 If instead the increment were placed before the output the first output is 00000001 and this is not as specified This error is not evident in the Run mode but is detected if the program is single stepped from the top hit Pause initially rather than Run Inversion Error This is a logical error that causes the opposite effect to that required For example if the exclamation mark is omitted before the input function the output runs when the button
89. with the current count after each clock and the status flag set when they match This is a more elegant method of modifying the time out period which can be used in generating a pulse width modulated PWM output A typical application is to control the output power to a current load such as a small DC motor more on this later In the capture mode the timer count is captured copied to another register at the point in time when an external signal changes at one of the MCU pins This can be used to measure the length of an input pulse or the period of a waveform The 877 has three counter timer registers Timer0 has an 8 bit counter and 8 bit prescaler It can be clocked from the instruction clock or an external signal applied to RA4 The prescaler can also be used to extend the watchdog timer interval see later in which case it is not available for use with Timer0 Timer1 has a 16 bit counter and prescaler and can be clocked internally or externally as per Timer0 It offers capture and PIC Microcontroller Systems 15 Input Volts Analog pa Inputs Multiplexer anx ieee Setup ADC Analog eres Read ADC to Digital Converter 8 bit or 16 bit m Integer Result Reference Volts _ _ V Figure 1 6 ADC Operation compare modes of operation Timer2 is another 8 bit counter but has both a prescaler and postscaler up to 1 16 and a compare register for period control Further details are provided in In
90. 0 Continue until data 00 while l1 Done kkxkkxkxkxkxkxkxkxkkxkxkxkkkkxkxkxkkkkxkkxkxkkkkkxkxkkxkx k C Peripheral Interfaces 129 z Tena aal 1 0N__OFF 5 A Fa OSC1 CLKIN RBO INT 34 7 SQUARE OSC2 CLKOUT RB1 35 SINE BL MCLR Vpp THV RB2 35 7 TRIANG RB3 PGM 37 cr ARBIT C RAO ANO RB4 55 RA1 AN1 RBS 35 WAVEFORM Dm RA2 AN2 VREF RB6 PGC 75 RA3 AN3 VREF RB7 PGD 1 PERIOD uP RA4 TOCKI_ 15 RA5 AN4 SS RCO T10SO T1CKI gt RC1 T10SI CCP2 o e t 1 PERIOD DOWN o o OUTPUT AMPLITUDE REO ANS AD RC2 CCP1 L 1 restart RE1 AN6 WR RC3 SCK SCL 8 oe RE2 AN7 CS RC4 SDI SDA 5 gt nowave RV2 22k 24 RC5 SDO o o e MCLR Vpp THV RC6 TX CK 2 E id RC7 RX DT u1 Q 19 12 3 RDO PSPO A8 VEE RD1 PSP1 20 11 a7 comp 16 JE 21 10 Ag 100nF RD2 PSP2 51 A i 3 RD3 PSP3 2 2f A5 IOUT RD4 PSP4 A4 10k R3 RDS PSPs Zt a3 VREF 5 4 3 RDG PSP6 a S a2 a RD7 PSP7 Al VREF 1o _ R1 PIC16F877A DACO808 outeu tle ie OFFSET B m Q 15V R2 15k Svi R4 7k5 Figure 3 12 Waveform Generator The program source code is shown in Listing 3 13 This is only a demonstration of the digital waveform generator principle
91. 0 points Start Button Temperature Controller gt Heater Stop Button Temp OK Indicator Running Indicator TEMPCON Initialize MCU ADC Functions Wait for Start Switch on Running Loop Read temperatur If too low Switch on Heater If too high Switch on Fan 268 Answers 10 11 12 13 If OK Switch on TempOK Always 10 points A data logger often needs to record analog input values from sensors Flash ROM is nonvolatile so data are retained during power off and the serial interface uses only two pins on the MCU A serial link is needed to upload the acquired data to a host system In a polled system the time between input samples may vary if the processing time changes between samples A timer interrupt forces the execution of an ISR containing the input sampling event at fixed intervals In a system with multiple interrupts each is assigned a numerical priority in relation to the others such that a high priority ISR is not interrupted by a lower priority one but a low priority interrupt may be interrupted by a high priority task The PC operating system is a priority interrupt driven multitasking OS optimized for file processing so that the time response of the system to real time events is not predictable The real time operating system is designed to provide a predictable response time to major system events as required in control systems
92. 00 MOVLW 0 but this is listed in the hex file as 0030 indicating that in program memory the low byte is at the lower even address which is logical The whole program is 40 bytes 80 hex digits ending at 6300 and highlighted in bold Additional configuration data follow and the file ends with the MCU identifier outbyte 1lst This contains the intermediate assembly language version of the program plus the configuration fuse settings When viewed in a text window it can be seen that the configuration code is 3F73h consistent with the program code outbyte cof This file contains the machine code plus source file information that allows debugging tools to display the source code and variables using their original labels This file is attached to the MCU in Proteus VSM to support source code debugging Listing 1 2 Program hex File 1000000000308A0004280000840183131F30830518 1000100083161F149F141F159F1107309C00880121 08002000FF3083128800630029 02400E00733FFE 00000001FF PIC16F877A 26 Part 1 outbyte MPLAB IDE v7 52 Fle Edt View Project Debugger Programmer Tools Configure Window Help DSH Aa GAS RelaevosRBO amp cuPHRrrk E outbytemew O X m C outbyte c COR Disassembly Listing rr gt 1 0 PIC BOOKS PIC Programming book Ap A S Cl outbytemep OUTBYTE C MPB 2 1 0 4 n s CI Source Fies 7 0000 xoviw 0 E oubyte 0003 MOVUF Oza a C Header Files flinclude 16F877A h 9002 GOTO O
93. 07 Serial I O using SPI synchronous link Simulation hardware SPI DSN receiver program attach to U3 include 16F877A h void main RRR kkk kkk kk kkk kkk kkk kk kkk kkk k kk kk int recnum setup_spi spi_slave Set SPI slave mode while 1 recnum spi_read Read BCD code at SPI port output_D recnum Display it addressing This means that only two signals are required data and clock see Section 1 4 for details The test system shown in Figure 3 9 has only one I C peripheral device the 24AA256 serial flash memory chip to keep it as simple as possible Serial memory is a common feature of applications that require additional data storage such as a data logger It allows the internal EEPROM of the PIC to be expanded using only two I O pins The downside is that the memory access is rather slow with the maximum write cycle time of 5 ms 200 bytes sec specified for this device Therefore the data sampling rate needs to be suitably modest The serial memory chip has a capacity of 256 k bits or 32 k bytes with three external address pins AO Al and A2 This allows a set of up to eight chips to be used in the system each with a different hardware address 0 7 This address is included in the address code sent by the master controller so that a specific address in a selected chip can be accessed With eight 32 k chips the total address space is 256k In the test system the memor
94. 1 Capture Signal gt Capture Register Timer Instruction Clock gt Clock Prescaler fi Postscaler Overtlow Source Clock Output gt Time out External Pulse Select Divide Divide Interrupt Flag Compare Register Match Flag Figure 1 5 General Timer Operation determines the maximum count 256 or 65536 respectively When the timer register overflows and returns to zero an overflow flag bit is set This flag can be polled tested to check if an overflow has occurred or an interrupt generated to trigger the required action To modify the count period the timer register can be preloaded with a given number For example if an 8 bit register is preloaded with the value 156 a time out occurs after 256 156 100 clocks Many timer modules allow automatic preloading each time it is restarted in which case the required value is stored in a preload register during timer initialization A prescaler typically allows the timer input frequency to be divided by 2 4 8 16 32 64 or 128 This extends the maximum count proportionately but at the expense of timer precision For example the 8 bit timer driven at 1 MHz with a prescale value of 4 counts up to 256 X 4 1024 us at 4 us per bit A postscaler has a similar effect connected at the output of the counter In the compare mode a separate period register stores a value that is compared
95. 1 0 0 1 1 1 0 1 OxFD 1 0 1 0 0 0 0 O 0x60 2 0 1 1 0 0 OxDB 3 1 0 0 OxF3 4 0 1 0 0 O 0x66 5 0 0 0 OxB7 6 0 0 T OxBF 7 0 0 0 0 O OxEO 8 1 1 1 OxFF 9 0 0 1 OxE7 0 0 0 0 0 0 0 0 Blank Each group of segments associated with each common connection on the LCD is operated in turn by the program The LCD functions used are setup_lcd and 1lcd_symbol The arguments of the setup function specify a 14 pin display module and 0 clock divide factor The clock rate controls the display multiplexing rate which can be modified for best visibility The arguments of the output function comprise an 8 bit map for the numeral to be displayed as a hex number Table 4 6 and a list of the corresponding bits in the LCDDATAx locations for that digit The 8 bit numeral codes are shown in Figure 4 7 Because of the interaction of the control lines the LSB for each code was determined by inspecting the results on the display Otherwise the mapping is as normally required for seven segment codes The mapping data for each segment is provided to the output function in the form of a list of segment bit addresses 0 95 To include information about which COM line is active for each bit the address is supplied as the sum of the start address of each COM block and the bit number within that block Therefore the bit address of segment A of digit 1 DIG1 is COMO 22 COMO has the value 0 COM1 24 COM2 48
96. 2 4 Its value can be determined by following the process of conversion that comes next which is the easiest way to describe the FP format The 32 bit FP number given is 1000 0011 1101 0010 0000 0000 0000 0000 Table 2 3 Microchip CCS Floating Point Number Format Exponent Sign Mantissa eeee eeee s mmm mmmm mmmm mmmm mmmm mmmm 8 bits 1 bit 23 bits Table 2 4 Example of 32 Bit Floating Point Number Format FP number 1000 0011 1101 0010 0000 0000 0000 0000 Mantissa 101 0010 0000 0000 0000 0000 Exponent 1000 0011 y Sign 1 negative number C Programming Essentials 51 The mantissa is the low 23 bits and the set bit weighting gives the value 1 2 1 8 1 64 0 5 0 125 0 015625 0 640625 Then 1 is added to shift the decimal part into the range between 1 9999999 and 1 000000 Decimal number 1 640625 Signed result 1 640625 The exponent is given by the high byte 1000 0011 1314 This includes an offset of 127 to allow for positive and negative exponents so we subtract 127 to obtain the corrected exponent 131 127 4 The multiplier value is then calculated from the binary exponent 2 16 The final value is found by multiplying this by the mantissa result 16 xX 1 640625 26 25 The range of numbers that can be represented by the FP format can be estimated from the exponent range Minimum exponent value 277 107 Maximum exponent value 277 10738 Th
97. 3 1 66 V VLCD2 RC1 16 LCD control voltage 2 2 Vgq 3 3 33 V VLCD3 RC3 17 LCD control voltage 3 Vag 142 Part 4 Table 4 2 Mechatronics Board User Connections User input devices SW2 General purpose tactile switches active low SW3 use RAO RA1 RA3 RA4 RAS RA6 RAZ sw4 POT1 Manual analog input 0 5V for ADC and comparator POT2 use AN1 C1 AN2 AN3 C1 AN4 Sensor inputs TEMP Temperature sensor 10mV C 0 C 500 mV use AN1 AN4 LIGHT Light sensor 0 5 V use C1 and C1 Table 4 3 DC Motor Connections Label Alt Func MCU Pin DC motor output J1 Pl RD7 Enable source current driver stage 1 PWM1 CCP1 Pulse width control driver stage 1 N1 RD6 Enable sink current driver stage 1 P2 RD5 Enable source current driver stage 2 PWM2 CCP2 Pulse width control driver stage 2 N2 RD4 Enable sink current driver stage 2 DC motor sensors OPTINT J7 Optical interrupter 2 pulses per rev use CCP1 BACKEMF J16 Back EMF 0 5 V use RA1 CSENSE J15 Current measurement 1 mV mA use RA1 All bridge drives are connected to ground via a 0 1 Q current sensing resistor which produces a voltage proportional to the load current This is fed to an amplifier and comparator so that the current can be measured The comparator triggers a fault condition if the current exceeds 1 A 100 mV across the sensing resistor which shuts down
98. 5 B3 RD4 e D4 Figure 4 5 Block Diagram of Test Hardware Configuration Listing 4 1 Test Program Outline TEST Include 16F917 header file Use delay library routines Count 0 Loop always Output count at Port D Delay 10ms Increment count Listing 4 2 Mechatronics Board Test Program TEST C MPB 14 4 07 First program for testing Mechatronics Board Flashes 4 LEDs total cycle time 256x10ms 2 56s Connect RD7 D7 RD6 D6 RD5 D5 RD4 D4 include 16F917 h Device header file use delay clock 8000000 Delay function clock speed void main Start main block int n 0 Count loop variable while 1 Endless loop output_D n Show on LEDs delay_ms 10 Wait 10ms between steps nt Increment loop count End of source code C Mechatronics Applications 145 A program implements a simple output loop which increments the binary count at Port C The PIC 16F917 outputs RD4 to RD7 need to be connected to the LEDs D3 to D7 on the target board with link leads on the connector pins The ICD2 module is plugged into the board via the ICD connector and to a host PC USB port The source code is loaded or edited in the usual way within MPLAB and saved in a project folder called test The source code and device header file are placed in the project folder and attached to the project in the project file window Assuming the C compiler has
99. 683 BSF 0x3 0x5 0073 286B GOTO 0x6b Note the redundancy in the sequence the pin data direction setting is repeated in each statement where the file register bank is selected BCF 0x3 0x5 and the direction bit is cleared to 0 BCF 0x8 0 Assembler Block The maximum output frequency of the pulse waveform can be increased by using a small assembler block to toggle the output bit A program is shown in Listing 2 22 that outputs a pulse train when a button connected to RBO input is pressed active low The main program provides initialization of the button interrupt and an assembler block which outputs the signal in a loop that is as short as possible The interrupt routine at the top of the program is called when the button is not pressed default condition switching off the output and waiting for the button to be pressed again to resume the output The start of the assembler block is identified by the asm directive and terminated with endasm All the code between these points must conform to the PIC assembler syntax requirements see Instruction Set Table 2 11 The interrupt still works even though it is set up in C because ultimately the interrupt control settings are the same in C and assembler Listing 2 23 disassembles the assembly block Note that the compiler automatically includes the necessary file register bank select command to access the port data bits Port B bit 0 is then set cleared and the GOTO
100. 6F917 TEMP1 C Temp Sensor 10mv C 0 C 500 mV LCD 2 digits ANO Figure 4 12 Temperature Sensor System temperature is converted and displayed The program TEMPDIS outline is given in Listing 4 14 and the source code in Listing 4 15 The ADC is set to 10 bit conversion giving an output of 1024 steps Internal ADC reference voltage 5 00 V Bit resolution 5 00 1024 4 88 mV per bit Temperature measurement 10 mV per C Temperature resolution 4 88 10 0 488 C per bit The temperature is therefore measured to about 0 5 C This is quite acceptable as the display is precise to only 1 C By contrast if 8 bit conversion were used the precision would be only about 2 C per bit and the display would be misleading Listing 4 14 Outline of Temperature Sensor Test Program TEMPDIS Select MCU 16F917 Include LCD functions Setup LCD Setup ADC 10 bits ANO Main loop Read analogue input binary 0 1024 Convert to temperature value integer Convert to BCD digits Display on LCD 0 99 Listing 4 15 Temperature Display Source Code TITTITTTTTT IATA TATA TT ATTA TITAS TTT TEMP1 C MPB 24 4 07 Demo program for PICDEM Mechatronics Board Displays temperature 1 0 deg C Target board link TEMP ANO TIITITITTATI TTA AT include 16F917 h device ADC 10 include lcd inc void main int16 intemp float temp int8 dis
101. CPD NOWRT This corresponds to all the bits of configuration register being default high 1 3 PIC16 MCU Peripherals e Digital I O e Timers e A D converter e Comparator e Parallel slave port e Interrupts Basic digital input and output I O in the microcontroller uses a bidirectional port pin The default pin configuration is generally digital input as this is the safest option if some error has been made in the external connections To set the pin as output the corresponding data direction bit must be cleared in the port data direction register e g TRISD Note however that pins connected to the analog to digital A D converter default to the analog input mode The basic digital I O hardware is illustrated in simplified form in Figure 1 4 with provision for analog input The 16 series reference manual shows equivalent circuits for individual pins in more detail For input the current driver output is disabled by loading the data direction bit with a 1 which switches off the tristate gate Data are read into the input data latch from the outside world when its control line is pulsed by the CPU in the course of a port register read instruction The data are then copied to the CPU working register for processing When the port is set up for output a 0 is loaded into the data direction bit enabling the current output The output data are loaded into the data latch from the CPU A data 1 at the output allows the current driver to
102. CU PIC 18 only PIC others PIC only Mainly PIC Mainly PIC targets Primary Any Any Any Proprietary Proprietary target single board modular hardware Function Extensive Standard Good Extensive Standard libraries libraries peripheral libraries only peripheral peripheral only support support support Tutorial Comprehensive Comprehensive Free Comprehensive Tutorial in package or user free download free download download free download only manual Relative PIC16 n a PIC16 995 16F87X 50 PIC16 18 249 PIC16 99 price PIC18 495 PIC18 995 PIC16 150 PIC24 249 PIC16 18 180 single PIC24 895 PIC24 1195 PIC18 200 user PIC24 250 Demo Function Time limited Time and None None version limited student evaluation memory edition version limited demo Origin US US US EU UK Approximate Microchip C18 and Hi Tech C are designed primarily for professional use as reflected in the relatively high price but this is compensated for by the provision of feature limited freeware versions For any development engineer who will be using mainly PIC 18 or above parts the C18 offers the advantage of extensive function libraries Bear in mind though a separate compiler C30 is needed for PIC24 and dsPIC devices although one can assume an easy progression route from C18 For those intending to use a wider range of MCU types Hi Tech might be preferred Hi Tech PICC Lite offers good functionality in a limited range of PIC 16 devices in
103. D Each compiler has a set of header files provided all of which have a similar function of defining the register and control bit labels for all the supported processors The exact labeling system can vary although the labeling used in the PIC hardware manuals must be preferred Microchip C18 Microchip does not supply a compiler for the mid range 16 series MCUs It is assumed that any application developed in C will be run on an 18 series processor or above This is because the mid range devices have limited memory capacity and many commercial C applications exceed this limit Nevertheless it is well worth looking at C18 because having learned C on the 16 series the reader may wish to consider the option of progressing to the 18 series for further work The full list of features claimed for this compiler as listed in the C78 User Guide www microchip com includes e ANSI 89 compatibility e Integration with the MPLAB IDE for easy to use project management and source level debugging e Generation of relocatable object modules for enhanced code reuse e Compatibility with object modules generated by the MPASM assembler allowing complete freedom in mixing assembly and C programming in a single project e Transparent read write access to external memory e Strong support for in line assembly when total control is absolutely necessary e Efficient code generator engine with multilevel optimization e Extensive library suppor
104. D2 f input PIN_D3 akey 0x36 delay_ms 50 while input PIN_D3 H H C Programming Essentials 73 H f input PIN_D4 akey 0x2A delay_ms 50 while input PIN_D4 output_b 255 output_low PIN_B4 if input PIN_D1 akey 0x31 delay_ms 50 while input PIN_D1 if input PIN_D2 akey 0x32 delay_ms 50 while input PIN_D2 if input PIN_D3 akey 0x33 delay_ms 50 while input PIN_D3 f input PIN_D4 akey 0x2D delay_ms 50 while input PIN_D4 H output_b 255 output_low PIN_B5 if input PIN_D1 akey OxFF putc 254 putc 1 delay_ms 500 f input PIN_D2 akey 0x30 delay_ms 50 while input PIN_D2 if input PIN_D3 akey 0x3D delay_ms 50 while input PIN_D3 f input PIN_D4 akey 0x2B delay_ms 50 while input PIN_D4 H ct H The program incorporates a procedure makenum to generate a one two or three digit integer from the individual input digits and scankey to read each keystroke The functions are declared as prototypes before main this allows the functions to be defined after main This is sometimes more logical the main block is designed first and the details within the functions developed afterward The main block is a continuous loop defined by the c
105. DECFSZ 78 F 0010 GOTO 00C 0011 MOVLW 4A 0012 MOVWF 77 0013 DECFSZ 77 F 0014 GOTO 013 0015 GOTO 016 0016 DECFSZ 00 F 0017 GOTO 00A 0018 BCF 04 3 0019 BCF 0A 4 001A GOTO 039 RETURN 001B CLRF 04 001C BCF 03 7 001D MOVLW 1F 001E ANDWF 03 F 001F BSF 03 5 0020 BSF 1F 0 0021 BSF 1F 1 0022 BSF 1F 2 0023 BCF 1F 3 0024 MOVLW 07 0025 MOVWF 1C Software Design Using CCS C 217 Load delay value high byte 01 Load delay value low byte 00 Decrement low counter and repeat x255 765us Decrement high counter and do not repeat Load low counter with 0x4A 74 Decrement low counter and repeat x73 219us Next step Decrement delay value and repeat 1ms delay loop x9 Select program memory page zero Jump back to main block START OF MAIN BLOCK xe KXXKKKX Set FSR pointer 0 Select File Bank 0 1 for indirect addressing Select File Bank 0 for direct addressing Select File Bank 1 Select analogue input mode 8 Switch off comparator inputs File register 0x21 GPR1 appointed as x START OF MAIN LOOP 218 Appendix B 0029 BSF 03 5 002A BSF 05 4 002B BCF 03 5 002C BTFSC 05 4 002D GOTO 036 0026 MOVLW FF 0027 BCF 03 5 0028 MOVWF 20 002E MOVLW 00 002F MOVWF 20 0030 BSF 03 5 0031 CLRF 07 0032 BCF 03 5 0033 MOVF 21 W 0034 MOVWF 07 0036 MOVLW 0A 0037 MOVWF 22 0038 GOTO 004 Configuration Fus
106. DIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF 0000 0000 26 150 ODh PIR2 CMIF EEIF BCLIF CCP2IF 0 0 0 0 28 150 OEh TMRIL Holding Register for the Least Significant Byte of the 16 bit TMR1 Register xxxx xxxx 60 150 OFh TMR1H Holding Register for the Most Significant Byte of the 16 bit TMR1 Register xxxx xxxx 60 150 10h T1CON T1CKPS1 T1CKPS0 T1OSCEN TISYNG TMRICS TMRION 00 0000 57 150 11h TMR2 Timer2 Module Register 0000 0000 62 150 12h T2CON TOUTPS3 TOUTPS2 TOUTPS1 TOUTPSO TMR2ON T2CKPS1 T2CKPS0 000 0000 61 150 13h SSPBUF Synchronous Serial Port Receive Buffer Transmit Register xxxx XXXX 79 150 14h SSPCON WCOL SSPOV SSPEN CKP SSPM3 SSPM2 SSPM1 SSPMO 0000 0000 82 82 150 15h CCPRIL Capture Compare PWM Register 1 LSB xxxx xxxx 63 150 16h CCPR1H Capture Compare PWM Register 1 MSB XxXxx xxxx 63 150 17h CCP1CON CCP1X CCP1Y CCP1M3 CCP1M2 CCP1M1 CCP1MO 00 0000 64 150 18h RCSTA SPEN RX9 SREN CREN ADDEN FERR OERR RX9D 0000 000x 112 150 19h TXREG USART Transmit Data Register 0000 0000 118 150 1Ah RCREG USART Receive Data Register 0000 0000 118 150 1Bh CCPR2L Capture Compare PWM Register 2 LSB xxxx Xxxx 63 150 1Ch CCPR2H Capture Compare PWM Register 2 MSB xxxx xxxx 63 150 1Dh CCP2CON CCP2X CCP2Y CCP2M3 CCP2M2 CCP2M1 CCP2M0 00 0000 64 150 1Eh ADRESH A D Result Register High Byte xxxx xxxx 133 150 1Fh ADCONO ADCS1 ADCSO CHS2 CHS1 CHS
107. EEPROM location Ut Pa OSC1 CLKIN RBO INT 5 1 A 14 OSC2 CLKOUT RB1 35 3 2 RB2 f 36 4 lt RAO ANO RB3 PGM 3 37 5 77 RAVAN RB4 55 5 4 5 RAZ AN2 VREF CVREF RB5 35 RAS ANS VREF RB6 PGC a RA4 TOCKI C10UT RB7 PGD RAS AN4 SS C20UT m O RCO T1OSO T1CKI R1 R2 REO ANS RD RC1 TIOSI CCP2 Ne Ik o RE1AN6 WR RC2 CCP1 12 RE2 AN7 CS RC3 SCK SCL E i RC4 SDI SDA E2 MCLR Vpp THV RC5 SDO 5E l RO6 TX CK E i R een RC7 RX DT S 5 Ee 19 1 16 3 18 1 Step RDO PSPO R W 20 2 15 4 17 je RD1 PSP1 4 c 2i 8 14 5 16 C1 RD2 PSP2 21 43 T i l6 s 5 RD3 PSP3 5E 4 15 RD4 PSP4 4 O 28 6 11 8 13 RDS5 PSP5 4 29 7 10 9 12 RD6 PSP6 e 2 5 T i2 o RD7 PSP7 o PIC16F877A Figure 3 11 EEPROM Test System C Peripheral Interfaces 127 address 0 The switch code is then changed and the next code stored in location 1 and so on until a 0 is entered on the switches As the data are stored each byte is displayed on the bar graph The R W switch is then opened to select read mode As the button is pressed the same sequence of stored codes is displayed from memory The nonvolatile data storage is demonstrated
108. EP Sets sleep delay time sleep_ulpwl time_in_us Selected MCUs only LOW VOLTS DETECT Triggers interrupt if supply low setup_low_ volt_detect lvd_33 Selected MCUs only Answers Assessment 1 1 Musical birthday card electronic price tag sound system television automobile robot Input ROM CPU RAM output Flash ROM is non volatile but reprogrammable so the program can be changed or the chip reused Program testing and modification is easier and development time is reduced compared with alternative types of program memory Number of I O pins program memory size RAM size EEPROM size maximum clock speed range of interfaces development system cost availability The program is stored as machine code instructions executed in sequence The instruction register holds the current instruction and the program counter holds its address The file registers store the program data and the working register the data being operated on 02 Program Counter Low Byte 03 Status Register 09 Port E Data Register 89 Port E Data Direction Register 20 General Purpose Register 1 RC clock uses resistor capacitor circuit to control clock frequency XT clock uses crystal circuit to control clock frequency WDT watchdog timer provides automatic reset if program hangs PUT power up timer delays the program start until the MCU is ready NOWRT prevents writes to pr
109. F file is attached 4 MHz is usually used in the demo circuits giving an instruction cycle time of 1 us This determines the programmed delay count required to give the specified output rate If the output LSB frequency is 50 Hz the period is 20ms The half cycle time then is 10 ms which is the required program delay Appendix B explains the program design process in more detail Software Design Using CCS C A program is to be designed to meet the specification given in Appendix A which describes how to develop the hardware design for this application The specification was as follows When a button is pressed the system generates an 8 bit binary count starting at 0 on a bar graph display The output frequency at the least significant bit is 50 Hz giving an overall cycle time of 2 56 sec The general form of a real time application is represented by the flowchart in Figure B 1 which shows two main phases initialization and main loop The initialization is executed once and the main loop repeats The program must be written to the syntax requirements of standard C with reference in this case to the CCS C User Manual Version 4 downloadable from as a PDF from www ccsinfo com The dialect of C developed by CCS Inc is tailored specifically to the features of the PIC microcontroller CCS supplies different complier variants for low middle and high performance PICs the mid range compiler PCM is used for the PIC 16F877A Reset Ini
110. General Purpose Register 96 Bytes 7Fh Bank 0 File Address Indirect addr 80h OPTION_REG 81h PCL 82h STATUS 83h FSR 84h TRISA 85h TRISB 86h TRISC 87h TRISD 88h TRISE 89h PCLATH 8Ah INTCON 8Bh PIE1 8Ch PIE2 8Dh PCON 8Eh 8Fh 90h SSPCON2 91h PR2 92h SSPADD 93h SSPSTAT 94h 95h 96h 97h TXSTA 98h SPBRG 99h 9Ah 9Bh CMCON 9Ch CVRCON 9Dh ADRESL 9Eh ADCON1 9Fh General AOh Purpose Register 80 Bytes EFh accesses FOh 70h 7Fh FFh Bank 1 Software Design Using CCS C File File Address Address Indirect addr 100h Indirect addr 180h TMRO 101h OPTION_REG 181h PCL 102h PCL 182h STATUS 103h STATUS 183h FSR 104h FSR 184h 105h 185h PORTB 106h TRISB 186h 107h 187h 108h 188h 109h 189h PCLATH 10Ah PCLATH 18Ah INTCON 10Bh INTCON 18Bh EEDATA 10Ch EECON1 18Ch EEADR 10Dh EECON2 18Dh EEDATH 10Eh Reserved 18Eh EEADRH 10Fh Reserved 18Fh 110h 190h 11h 191h 112h 192h 113h 193h 114h 194h 115h 195h General ne General ee Purpose 17h Purpose 197h Register 118h Register 198h 16 Bytes 4119h 16 Bytes 199h 11Ah 19Ah 11Bh 19Bh 11Ch 19Ch 11Dh 19Dh 11Eh 19Eh 11Fh 19Fh General 120h General 1A0h Purpose Purpose Register Register 80 B
111. IN_A4 Poll SW3 Debounce Not if min Wait switch Poll SW3 Debounce Not if max Wait switch void forward 4 steps clockwise speed output_D 0x20 output_D 0x40 output_D 0x10 output_D 0x80 delay_ms time delay_ms time delay_ms time delay_ms time Step 1 Step 2 Step 3 Step 4 void reverse 4 steps counter clockwise speed output_D 0x80 output_D 0x10 output_D 0x40 output_D 0x20 t delay_ms time delay_ms time delay_ms time delay_ms time Step 4 Step 3 Step 2 Step 1 162 Part 4 void main Main loop 1 1 1 1111111111110 while 1 Loop always while input PIN_A2 forward Run forward delay_ms 10 Debounce while input PIN_A2 Wait until released while input PIN_A2 reverse Run reverse delay_ms 10 Debounce while input PIN_A2 Wait until released in the algorithm is that the program checks the buttons only after four steps so the direction and speed do not change immediately if the motor is running at low speed This type of problem can be solved using interrupts 4 5 PICDEM Analog Sensors e Light switch application e Temperature display application The mechatronics board is fitted with a light and temperature sensor each of which produces an analog output
112. KIN rBoint HH aA 9 33 Ta 34 2 3q RBO INT OSC1 CLKIN 4 OSC2 CLKOUT RB1 iee H ret OSC2 CLKOUT MCLA Vpp THV RB2 32 5 5g RB2 MCLR Vpp THV 5 RB3 PGM 37 37 RB3 PGM RAO ANO RB4 322 37 RB4 RAO ANO J RATAN RBS seS H RBs RA1 AN1 RAZ AN2 VREF RBE PGC 37 i RN1 H RB6 PGC RA2 AN2 VREF RAS ANS VREF RB7 PGD 408 RB7 PGD RA3 AN3 VREF RA4 TOCKI i T RA4 TOCKI Z RA5 AN4 58 RCO TIOSO T1CK 5 RCO T1OSO T1CKI RA5 AN4 55 5 _ RCITIOSI CCP2 I 4 RC1 T10SI CCP2 a REo ANS RD RC2 CCP1 Z 5_3 RC2 CCP1 REO ANS RD_ Te REV ANGAWR Aca SCK SCL si RC3 SCK SCL RE1 ANG WR RE2 AN7 CS RC4 SDI SDA 23 15 RC4 SDI SDA RE2 AN7 CS RC5 SDO 24 RC5 SDO RC6 TX CK 23 9_7 RC6 TX CK RC7 RX DT 28 10 8 RC7 RX DT RDOIPSPO 42 270R 12 RDO PSPo RD1 PSP1 RD1 PSP1 RD2 PSP2 2t 21 RD2 PSP2 RD3 PSP3 22 22 RD3 PSP3 RD4 PSP4 21 S RD4 PSP4 RD5 PSP5 28 53 RDS PSP5 RD6 PSP6 28 23 RD6 PSP6 RD7 PSP7 RD7 PSP7 PIC16F877 U1 MASTER PIC16F877 U2 SLAVE Figure 3 10 PSP Test System Listing 3 10 PSP Master Test Program PSPMASTER C Test system master controller program design file PSP DSN U1 include 16F877A h void Iain RRR RRRRKERKRKEKKR RE RR KKK REE KKEKE REE KK KKK KEK int sendbyte port_b_pullups 1 Activate Port B pull ups while 1 sendbyte input_B Get test byte output_D sendbyte Output on PSP bus output_low PIN_E2 Select PSP slave output_low PIN_E1 Write b
113. KKEKKER KEKE ERK EERE EER EKER EKER ERE KEE RE RRR KER EERE EEE RKEEKRRERREREEKEEKR ERR KK include 16F877A h device ADC 8 8 bit conversion use delay clock 4000000 use rs232 baud 9600 xmit PIN_DO rcv PIN_D1 Display output void main L EAE Kk kk kkk kkk kkk kkk kkk kk kkk kkk kk kk EK k k k k kkk k k k k k kk k k k float refin numin temp int1 flag setup_adc ADC_CLOCK_INTERNAL Setup ADC setup_adc_ports ALL_ANALOG for Repeat always delay_ms 500 set_adc_channel 0 Read ref volts refin read_adc set_adc_channel 1 Read temp volts numin read_adc temp numin 50 256 Calc temperature putc 254 putc 1 delay_ms 10 printf Temp 3 0g temp Display temp putc 254 putc 192 delay_ms 10 if numin lt refin 10 Temp too low output_high PIN_B1 Heater on output_low PIN_B2 Fan off flag 1 if flag 1 printf Heater ON Status message if numin gt refin 10 Temp too high output_low PIN_B1 Heater off output_high PIN_B2 Fan on flag 0 if flag 0 printf Fan ON Status message 186 Part 5 X7 Reset gt LC Display Clock 4 MHz ICD lt gt X7 Toh r eypa ae E Vef 2 56 V Test Input PIC OLED gt 16F877A 0 2 5 V MCU gt Buzzer X7 User I O Serial Digital or m Memory
114. N 42 43 include directive 212 include files 224 include statement 36 212 Indirect addressing operators 75 7 Input voltage measurement and display 102 input PIN _nn 44 Instruction set for programming 90 1 93 4 INTCONbits TMROIF 0 statement 230 Integers 49 251 Intel 8051 2 Interintegrated circuit C serial bus 21 2 118 functions 121 test system 120 Interrupt 254 operation 190 1 in PIC16 peripherals 16 18 statements 107 8 Interrupt service routine ISR 17 190 274 Index Inversion error 224 ISIS schematic capture hardware design 203 design specification 203 4 schematic circuit 204 5 schematic edit 205 7 K Keypad and calculator 68 73 L Labcenter 203 227 lcd inc 152 1lcd_symbol function 151 152 156 LCDDATAx 147 Least significant bit LSB 108 LED flasher program 229 Light sensor 162 3 164 Linker errors 224 Liquid crystal display LCD 146 connections 146 9 control 248 segment connections 147 test program 149 52 Local variable 63 4 65 Logical errors 224 Loop control 42 44 Looping 41 2 Low cost in circuit debugging 2 Low pin count LPC 8 Low voltage programming mode 11 LP low power mode 9 M main function 60 62 73 210 makenum 73 Mantissa 49 math h library 131 Math functions 249 50 Matrix Multimedia C 227 234 6 Mechatronics board fixed connections 141 Mechatronics board user connections 142 Memory allocation 255 Memory read and write 254 Microchip 227 Microchip C18 227
115. O GO DONE ADON 0000 00 0 127 150 Legend x unknown u unchanged q value depends on condition unimplemented read as 0 r reserved Shaded locations are unimplemented read as 0 Figure B 3 PIC 16F877 Registers Bank 0 by permission of Microchip Technology Inc bank select bits RPO and RP1 are used for direct addressing but IRP is used for indirect addressing via the file select register FSR In this case the value in the register specified in the FSR is read or written at file address 00 The PIC internal architecture and register operations are fully explained in the 16F87XA data sheet downloadable from www microchip com Software Design Using CCS C 215 R W 0 R W 0 R W 0 R 1 R 1 R W X R W X R W X IRP RP1 RPO TO PD Z DC C bit 7 bit 0 bit 7 IRP Register Bank Select bit used for indirect addressing 1 Bank 2 3 100h 1 FFh o Bank 0 1 00 h FFh bit6 5 RP1 RPO Register Bank Select bits used for direct addressing 11 Bank 3 180 h 1FFh 10 Bank 2 100h 17Fh 01 Bank 1 80h FFh 00 Bank 0 00h 7 Fh Each bank is 128 bytes bit 4 TO Time out bit 1 After power up CLRWDT instruction or SLEEP instruction 0 A WDT time out occurred bit 3 PD Power down bit 1 After power up or by the CLRWDT instruction o By execution of the SLEEP instruction bit 2 Z Zero bit 1 The result of an arithmetic or logic operation is zero 0 The result of a
116. PIC B gt gt gt Warreng 202 C PIC B gt gt gt Waring 202 C PIC 8 k hibit JISFA ADCONO ww Add Sym o stow Symbol Name Value while 1 1 x01 hibyte OxFF hiword OxFFFF hilong xT EFEFFFE afloat 67 aletter Memory usage ROM OEnors 7 Weenings oaded C PIC BOOKS Px M D SUCCEEDED Sun Figure 2 5 Variable Types Demo Program Screenshot Character Variable Text characters are generally represented by ASCII codes Table 2 5 The basic set of 7 bit characters includes the upper and lower case letters and the numerals and punctuation marks found on the standard computer keyboard For example capital upper case A is 1000001 65 0 The numeric characters run from 0x30 0 to 0x39 9 so to convert to the actual number from ASCII simply subtract 0x30 The character variable is indicated in C source code in single quotes For example the statement answer Y will assign the value 0x59 to the variable answer Assignment Operations A range of arithmetic and logic operations are needed where single or paired operands are processed The result is assigned to one of the operand variables or a third variable Integers can be used for simple unsigned arithmetic operations giving an exact result However in general floating point numbers must be used for signed calculations but remember there will be small errors Logical operations must use integers as the numbers are processed bit by
117. Process the input processing may vary significantly depending on the input data or programmed options within the loop For example a test on the data may result in an optional sequence being executed or not depending on the value In fact this is pretty much inevitable in most real programs However it is often important for the input and output timing to be more predictable Take the example of motor speed control In small DC motors this is usually implemented by pulse width modulation as discussed in section 4 3 The output is switched on and off over a regular cycle the proportion of on to off time determining the average motor current and hence the speed To achieve accurate control the shaft speed must be measured usually by a pulse encoder The input pulse interval must be measured and the PWM duty cycle adjusted accordingly It is just about possible to do this using a polling process see PIC Microcontrollers An Introduction to Microelectronics by the author 2004 but a more elegant solution can be implemented using interrupts Interrupts As we have seen in Section 2 9 interrupts are internally or externally generated asynchronous hardware signals that force the processor to stop its current background task and carry out the interrupt service routine ISR a higher priority foreground task The processor context current register contents and status must be saved and the current program address stored
118. T ATTA AAT TAT TTT OUTPUT_x INPUT OUTPUT_HIGH OUTPUT_BIT 5x8 0 40 5x8 1 41 5x8 2 42 etc 6 8 0 48 etc 7 8 0 56 etc nolist Program memory 8192x14 Data RAM I O 33 Analog Pins 8 Data EEPROM 256 C Scratch area 77 ID Location Fuses LP XT HS RC NOWD1 Fuses NOPRO Fuses NOWRT WRT_25 WRT_5 111111 Discrete I O Functions SET_TRIS_x PORT_B_PULLUPS OUTPUT_LOW OUTPUT_FLOAT Constants used to identify pins in the above are define PIN_AO 40 Register 05 pin 0 define PIN_A1 41 Register 05 pin 1 define PIN_A2 42 Register 05 pin 2 define PIN_A3 43 Register 05 pin 3 define PIN_A4 44 Register 05 pin 4 define PIN_A5 45 Register 05 pin 5 define PIN_BO 48 Register 06 pin 0 define PIN_B1 49 Register 06 pin 1 define PIN_B2 50 Register 06 pin 2 define PIN_B3 51 Register 06 pin 3 define PIN_B4 52 Register 06 pin 4 define PIN_B5 53 Register 06 pin 5 define PIN_B6 54 Register 06 pin 6 define PIN_B7 55 Register 06 pin 7 define PIN_CO 56 Register 07 pin 0 define PIN_C1 57 Register 07 pin 1 define PIN_C2 58 Register 07 pin 2 define PIN_C3 59 Register 07 pin 3 define PIN_C4 60 Register 07 pin 4 define PIN_C5 61 Register 07 pin 5 define PIN_C6 62 Register 07 pin 6 define PIN_C7 63 R
119. T TTT TTT ATT TTT ART Constants used in setup_uart are FALSE Turn UART off TRUE Turn UART on define UART_ADDRESS 2 define UART_DATA 4 111 11 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 _ COMP Comparator Variables C1OUT C2OUT Constants used in setup_comparators are see 16F877 data sheet figure 12 1 define A0_A3_A1_A3 Oxf ff04 Two common reference comparators define A0_A3_A1_A2_OUT_ON_A4_A5 Oxfcf03 Two independent comparators with outputs define AO_A3_A1_A3_OUT_ON_A4_A5 Oxbcf05 Two common reference comparators with outputs define NC_NC_NC_NC Ox0ff07 Comparator inputs disconnected define AO_A3 Al A2 Oxff 02 Two independent comparators define AO_A3_NC_NC_OUT_ON_A4 Ox9ef01 One independent comparator with output define AO_VR_A1_VR Ox3 06 Two comparators with common internal reference define A3_VR_A2_VR Oxcff 0e Two comparators with common internal reference bit C1LOUT 0x9c 6 bit C2OUT 0x9c 7 84 Part 2 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 _NREE Constants used in setup_vref are define VREF_LOW Oxa0 Comparator reference voltage low range 0 3 75V nominal define VREF_HIGH 0x80 Comparator reference voltage high range 1 25V 3 75V nominal
120. TimerO 14 109 Timer 14 15 109 190 1 Timer2 15 190 Timers 13 15 245 Timestep per Frame settings 224 Timing error 225 6 Trigonometric functions 251 Type conversions 252 U Universal synchronous asynchronous receive transmit USART 19 20 vV Variables 40 1 types 47 240 character variable 52 53 floating point 49 51 integers 49 signed integers 49 Virtual oscilloscope screenshot 225 void change 132 void isrext 107 void main 36 38 Voltage measurement 100 3 W while loops 41 45 56 7 while 1 statement 73 210 219 WHILOOP C 44 Watchdog timer WDT 9 10 Waveform generator 129 X XT mode 9
121. VE Read an input string to astring fgets spoint 01 SELECTED character array RS232 CHECK SERIAL Check for serial input s kbhit activity RS232 PRINT ERROR Write programmed error assert a lt 3 message The program listed as HARDRS232 C Listing 3 6 is attached to the MCU in the simulator The getc function is used to read a character from the virtual terminal it waits for user input The terminal must be activated by clicking inside terminal window and the computer keyboard then provides the input to the PIC as the corresponding ASCII codes these are assigned to the variable incode as they arrive The ASCII code can be output using print f If formatted as a decimal the numerical value of the character code is displayed Alternatively the character formatting code c is used to display the character itself The function putc 13 outputs the code for a line return on the display If putc is used to output an ASCII code the character is displayed C Peripheral Interfaces 115 RB7 POD S ASCII RCO T10SO TICH __ so REATAOSWCCR2 REO ANSIRD_ RC2ICCP4 REV ANG WR RCSISCKISCL RE2 ANT CS RC4 SDIISDA RCSISDO RCBITXICK RC7 RX DT RDO PSPO RD1 PSP1 RD2 PSP2 RD3 P SP3 ROGIPSPS ROS PSPS ROG PSP6 RD7 PSP7 PIC16F877 TEXT Figure 3 7 RS232 Peripheral Simulation Listing 3 6 Hardware UART Demo Program HARDRS232 C MPB 13 6 07 Serial I O usin
122. _D1 intl minbit 0 maxbit 1 signed int8 minbyte 127 maxbyte 127 signed int16 minword 32767 maxword 32767 signed int32 minlong 2147483647 maxlong 2147483647 float testnum 12345 6789 void main delay_ms 1000 Wait for LCD to wake putc 254 putc 1 Home cursor delay_ms 10 Wait for LCD to do while 1 printf Bit d or d minbit maxbit delay_ms 1000 putc 254 putc 1 delay_ms 10 printf Byte d to d minbyte maxbyte delay_ms 1000 pute 254 putc 1 delay_ms 10 printf Word Ld minword putc 254 putc 192 delay_ms 10 printf to Ld maxword delay_ms 1000 pute 254 putc 1 delay_ms 10 3 printf Long Ld minlong putc 254 putc 192 delay_ms 10 printf to Ld maxlong delay_ms 1000 pute 254 putc 1 delay_ms 10 oe printf Float 5 4g testnum putc 254 putc 192 delay_ms 10 printf or e testnum delay_ms 1000 putc 254 putc 1 delay_ms 10 row is detected on the column input for that key which allows a corresponding code to be generated This is a binary number or ASCII code as required by the particular application Program CALC C Listing 2 17 runs on this hardware and implements a simple calculator with limited range 70 Part 2
123. a little more detail Unlike the conventional microprocessor system such as a PC which has separate chips on a printed circuit board the microcontroller contains all these elements in one chip The MCU is essentially a computer on a chip however it still needs input and output devices such as a keypad and display to form a working system The microcontroller stores its program in ROM read only memory In the past UV ultraviolet erasable programmable ROM EPROM was used for prototyping or 2 Part 1 ae l Input Output I a tas OSREINPUI o Peripherals CPU Peripherals a User Ouip uia L Program ROM Central RAM Download Read Only gt Processing Read amp Write Soa a Memory Unit Memory Figure 1 1 Elements of a Digital Controller small batch production and one time programmable ROM for longer product runs Programmable ROM chips are programmed in the final stages of manufacture while EPROM could be programmed by the user Flash ROM is now normally used for prototyping and low volume production This can be programmed in circuit by the user after the circuit has been built The prototyping cycle is faster and software variations are easier to accommodate We are all now familiar with flash ROM as used in USB memory sticks digital camera memory and so on with Gb 10 byte capacities commonplace The range of microcontrollers available is expanding rapidly The first to be widely use
124. able F 20 Memory Allocation INCLUDE STDLIBM H Function Description Example Comment MEMORY BLOCK Reserves a block of apl Allocated block 25x5 ALLOCATE memory calloc 25 4 bytes MEMORY BLOCK Releases a memory block free ap1 Previously allocated at DEALLOCATE address pointer ap1 MEMORY BYTES Reserves a number of apl Allocated block 14 ALLOCATE bytes malloc 14 bytes MEMORY BLOCK Copy a given numberof memcpy Copy n bytes from ap1 COPY bytes apl ap2 n toap2 MEMORY BLOCK Movea given number of memmove Move n bytes from ap1 MOVE bytes apl ap2 n toap2 MEMORY BLOCK Initialize locations witha memset Loads integer val1 into SET given value apl vall numof locations from numofb apl Table F 21 Special Setup Requires Chip Header File Only e g 16F877A H Function Description Example Comment SETUP WATCHDOG Initialize watchdog setup_wdt Time out options from TIMER time out wdt_1152ms 18 ms to 2 304 sec RESET WATCHDOG Clear watchdog timer restart_wdt Watchdog timer is TIMER within the program normally reset before loop time out SETUP Connection of analog setup_ Selected MCUs only COMPARATORS comparators comparator AO_A3_A1_A2 VOLTAGE Specify the comparator setup_vref Options in device REFERENCE ref voltage vref_low 10 header file SETUP OPAMP Enable built in op amp where fitted setup_ opamp1 1 Selected MCUs only SETUP SLE
125. ad_adc 104 Part 3 3 2 PIC16 C Interrupts e C interrupt functions e Interrupt sources e External interrupt Interrupts allow an external event to initiate a control sequence that takes priority over the current MCU activity Typically the interrupt service routine ISR carries out some operation associated with the port or internal device that requested the interrupt Interrupts are frequently used with hardware timers which provide delays timed intervals and measurement A time delay can be implemented using a simple software counting loop but this has the disadvantage of tying up the processor while the delay executes A more efficient technique is to use a hardware timer running independently from the MCU clock This allows accurate timing to be more easily achieved and the timer can run concurrently with some other task A time out interrupt informs the MCU that the timer interval has expired and the ISR can implement the required action The interrupt has to be initialized for use at the top of the program C Interrupts The CCS C complier provides a set of functions that implement the PIC interrupt system Table 3 2 The interrupt sources available in the PIC16F877 are as listed in Tables 3 3 Table 3 2 CCS C Interrupt Functions Action Description Example INTERRUPT CLEAR Clears peripheral interrupt clear_interrupt int_timer0 INTERRUPT Disables peripheral interrupt disable_interrupt
126. age to overcome line impedance and interference Data transmission at TTL signal levels in the other links restricts the distance to within the same subsystem board unit or back plane For greater distances and multinode operation a local area network interface is required which provides synchronous data communication with unlimited software addressing and error correction 3 The SPI system can be expanded by additional address decoding and line drivers as necessary but there are practical limits to this option and 1 C or networking would probably be more effective 126 Part 3 3 8 PIC16 C EEPROM Interface e EEPROM test system e EEPROM test program The internal electrically erasable programmable read only memory block is not strictly speaking a peripheral as it is internal to the MCU but it is accessed in a way similar to external devices so it is included in this part In the 16F877 the EEPROM is a block of 256 bytes of nonvolatile read write memory It allows data to be retained while the power is off which is useful in applications such as an electronic lock where a secure code needs to be stored Figure 3 11 shows a test circuit that demonstrates its operation Arbitrary 8 bit codes are set on the switch bank which are stored recalled and displayed on the LED bank The R W Read Not Write input switch is closed to select the Write mode The switch code is set and the button pressed This stores the code in the first
127. al formatting 5X Hexadecimal SLX Long hex SC ASCII character corresponding to numerical value SS Character or string decimal places printed can also be specified for floating point numbers for example 5 3d displays a decimal number with five significant digits and three decimal places Keypad and Calculator A simple calculator application demonstrates the use of the LCD and a keypad as well as some numerical processing A matrix keypad provides a simple data entry device for microcontroller systems The keys are connected in rows and columns such that pressing a button connects a row to a column The required connections are shown in Figure 2 12 The rows labeled A B C and D are connected as outputs at Port B avoiding the programming pins The columns labeled 1 2 3 and 4 are connected as inputs on Port D and are pulled up to 5 V by 10 k resistors A serial LCD described previously is driven from pin 7 of Port D To read the keypad each row is set low in turn and the state of the inputs tested If no button is pressed all the inputs remain high When a key is operated a low on that C Programming Essentials 69 Listing 2 16 Formatted Variable Output to a Serial Display FLOAT C MPB 4 3 07 Displays variable types and ranges KREEKEKKKEKEKER ERE KEKE REE EKER ERK REE KEE REE EREKEREREKREERE include 16F877A h use delay clock 4000000 use rs232 baud 9600 xmit PIN_DO rcv PIN
128. allel control Page mode option Control Start Stop bits Clock strobe Clock strobe Start Read Write Chip Acknowledge Select Speed LOW lt 19 2 kb sec HIGH lt 5 Mb sec HIGH lt 1 5 Mb sec MID lt 40 X bits sec depends on mode 8 240 kb sec Distance HIGH lt 100m LOW lt 1m LOW lt 1m LOW lt 1m Nodes 2 only Unlimited 1024 10 bit address Limited by bus characteristics Systems Single peer to peer Master slave Master slave Master slave Operation Can be connected Simple clocked Complex software Simple hardware as a simple 2 data high speed control and addressing control but with wire system but but requires slave reduces speed but limited bus length has additional selection wiringand requires no slave Higher speeds handshaking modes possibly external selection wiring or possible using and parity checking decoding external decoding assembler routine for extra reliability hardware May need external decoding Typical PC host to MCU Sensor data Multiperipheral control Multiprocessor applications target data transfer e g data logger link MCU communication link system with sensors and low speed memory data storage system parallel MCU data link Notes 1 This is an estimated speed using nonoptimized C code to drive the bus If optimized assembler code were used this could be improved significantly Transmission distance in the UART is enhanced by using line drivers to increase the signal volt
129. and COM3 72 Therefore COMO 22 22 By the same process the single bit address 152 Part 4 controlling the MSD DIG4 is COM2 2 50 and the first decimal point DP1 is addressed at COM3 21 93 For convenience the lists of segment bit addresses for each digit are defined at the top of the program using the replacement text labels DIG1 DIG2 DIG3 and DIG4 plus the three decimal point addresses The 1cd_symbo1 function is then supplied with the constant array element number for the numeral to be displayed and the bit address list as DIGx A for loop outputs each numeral at each position in turn including the blank digit while the MSD and decimal points are switched on and off individually BCD Count Program Listing 4 4 shows a program that displays a decimal count on the LCD The count is generated as binary coded decimal BCDx digits Each digit is initialized to 0 then incremented until it reaches 10 when it is cleared back to 0 and the next most significant digit incremented The three digits are then displayed together The MSD DIG4 is not used The LCD data block is now concealed in a separate source code file Lcd inc which is included at the top of the program 4 3 PICDEM DC Motor Test Programs e Motor test program e Rev counter program The primary target device on the board is the DC motor The hardware configuration is shown in Fi
130. and sensors Describe briefly the function of EEPROM and its applications Why is external EEPROM sometimes necessary Explain why interrupts are used in the demo program DACWAVE to respond to manual input to change the output frequency Outline how a simple program could produce a high speed square wave using the hardware in Figure 3 12 Assignments 3 To undertake these assignments install Microchip MPLAB www microchip com Labcenter ISIS Lite www proteuslite com and CCS C Lite www ccsinfo com Application files may be downloaded from www picmicros org uk Run the applications in MPLAB with Proteus VSM selected as the debug tool Display the animated schematic in VSM viewer with the application COF file attached to the MCU see the appendices for details Assignment 3 1 Download the project ANALIN the 8 bit analog test project Run it and check that the output voltage is represented by a number between 0 and 8 Now modify the program to display the actual voltage bearing in mind that the reference value is 5V That is when C Peripheral Interfaces 135 the input is a maximum of 5 V the value received by the ADC will be 256 The scaling factor therefore is 5 256 19 5 mV bit The input therefore needs to be multiplied by 0 0195 to be displayed as voltage Floating point variables need to be used in the revised program Assignment 3 2 Download the project PWM and test it for correct operation A 250 Hz 4 ms pulse wa
131. ant operations For example when an I O operation is converted the compiler can check to see if the port is already correctly initialized if so repetition of the initialization can be eliminated from the code Alternatively sections of the program can be written directly in assembler Not only is the code more compact the timing is more predictable and execution faster Say that a fast pulse waveform is to be generated by toggling a port bit The maximum frequency depends on the number of instructions on the output loop If the sequence is implemented in C code a loop of two statements is required Listing 2 20 This compiles into the code seen in Listing 2 21 and we see that a sequence of nine assembler instructions is obtained Taking into account that the last instruction GOTO 0x6b takes two instruction cycles to complete the total loop time will be ten instructions If the MCU is clocked at 4 MHz each instruction takes 1 us and the whole loop 10s The period of the output then is 100 kHz Listing 2 20 C Code Fragment for Pulse Output Loop while 1 output_high PIN_DO output_low PIN_DO 88 Part 2 Listing 2 21 Disassembled Code for Pulse Output Loop 25 while 1 26 output_high PIN_DO 006B 1008 BCF 0x8 0 006c 1283 BCF 0x3 0x5 006D 1408 BSF 0x8 0 Qed output_low PIN_DO 006E 1683 BSF 0x3 0x5 0006F 1008 BCF 0x8 0 0070 1283 BCF 0x3 0x5 0071 1008 BCF 0x8 0 28 0072 1
132. are disabled If either sensor input is disconnected the most likely fault mode the fault output comes on and all other outputs are disabled The same effect is observed if the motor is stalled simulating a fan fault When the real system is commissioned the program values may need to be adjusted to optimize the system response In this kind of feedback system the system generally needs to respond as quickly as possible without showing instability The loop delay time wait for fan and the PWM calculation might need to be modified accordingly In commercial temperature controllers time constant and gain values are adjustable so that the system response can be optimized in situ Listing 4 16 outlines the temperature controller program 170 Part 4 Listing 4 16 Temperature Controller Program Outline TEMCON temperature control system Define amp Initialize StartIn RA5 0 1 StopIn RA6 0 1 LightIn RA1 0 255 TempIn RAO 0 255 SetTemp RA3 0 255 RunOK RD4 0 1 Sunlit 0 255 calibrate Startup All outputs disabled Loop Read store display SetTemp While Start button not pressed Main Loop Read InputTemp If InputTemp out of range Disable outputs Wait for reset Flash fault indicator If TempIn SetTemp lt 2 Switch on Heat1 Disable Fan If TempIn SetTemp lt 5 Switch on Heat2 Flash fault indicator If TempiIn SetTemp gt 1 Read FaniInt Calculate fan speed Cal
133. at one slave sender each would need a separate slave select line with only one being enabled at a time The individual programs were created as separate projects in MPLAB but saved in the same folder sharing a copy of the MCU header file The COF files were then attached to the corresponding chip in the simulated hardware Table 3 7 SPI Function Set Operation Description Example SPI SETUP Initializes SPI serial port setup_spi spi_master SPI READ Receives data byte from SPI port inbyte spi_read SPI WRITE Sends data byte via SPI port spi_write outbyte SPI TRANSFE Ps Sends and receives via SPI inbyte spi_xfer outbyte SPI RECEIVE 5 Checks if SPI data received done spi_data_is_in 117 C Peripheral Interfaces A1 i i pe u2 i i ie a4 23 RBo INT OSC1 CLKIN H RUEDA A5 3574 RB1 OSC2 CLKOUT TIPAT er A6 3g RB2 MCLR Vpp THV dob totais A7 57 RB3 PGM 5 4 4 4 b h 4 Ag 3g RB4 RAO ANO 3 Poiactoe aster st B1 0 7 39 RBS RA1 AN1 uoo ooo Bojo 7 m Jo RB6 PGC RA2 AN2 VREF 4 RB7 PGD RAS ANS VREF 2 ig RA4 TOCKI gt ii 4244 RCO TIOSOMICKI RA5 AN4 SS A 33 484 RC1 T10S1 CCP2 _ ta OSC1 CLKIN RBO
134. ata are returned a PSP b SPI UART d PC EEPROM is nonvolatile data storage which allows data to be stored while the power is off It can therefore store security codes and limited amounts of other key data long term It is limited in size so an external serial EEPROM can be used to expand it The output speed is critical in this application because the waveforms are generated by outputting a table of values to the DAC as fast as possible To minimize the output loop time interrupts are used instead of polling the switches The output frequency is thereby maximized An output bit can be toggled using an assembler sequence to minimize the loop time as shown in Section 2 8 In this circuit the output port needs to be switched between 0x00 and OxFF using output_portD n within a minimal loop to generate a fast square wave Assessment 4 1 See the figure pl SL Q2 zal i NMOSFET 0 10 11 Answers 265 Speed 6 steps sec 6 X 7 5 deg sec 45 deg sec 45 360 rev sec 60 8 7 5rpm Linear characteristic Output voltage V mt c t temperature Gradient m 10mV C At 0 C sensor voltage V 500mV so 500 c Hence V 10t 500mV The parallel display uses more MCU output pins drive requirements are more complex segment encoding required and it shows only 3 5 numerical digits while the serial LCD is 16x2 alphanumeric lcd_symbol DigMap 8 DIG1 The f
135. ata memory and allow some duplication of labels local variables may be defined within a function These then exist only for the duration of the function execution and are subsequently lost The value of local variables can be passed back to the calling function or should be defined as global so that the data are not lost when the function completes PIC Registers Some knowledge of the PIC internal architecture is useful at this point The MCU operation is controlled by a set of file registers which contain special function registers SFRs in the first 32 locations followed by some general purpose registers GPRs The 16F877 has four banks of 128 registers as shown in Figure B 2 Some registers are duplicated in more than one bank so the actual number of distinct GPRs is 192 Figure B 3 shows the function of each bit of the SFRs in BankO and Figure B 4 the details for the status register which contains the bank select bits Note that the file register File Address Indirect addr 00h TMRO O1h PCL 02h STATUS 03h FSR 04h PORTA 05h PORTB 06h PORTC 07h PORTD o8h PORTE 09h PCLATH OAh INTCON OBh PIR1 OCh PIR2 ODh TMRIL OEh TMR1H OFh T1CON 10h TMR2 1th T2CON 12h SSPBUF 13h SSPCON 14h CCPRIiL 15h CCPR1H 16h CCP1CON 17h RCSTA 18h TXREG 19h RCREG 1Ah CCPR2L 1Bh CCPR2H 1Ch CCP2CON 1Dh ADRESH 1Eh ADCONO 1Fh 20h
136. atement uses a function call in a similar format to CCS but of course the exact syntax is different Listing D 2 also includes other features not covered elsewhere in this book The pragma directive allows additional directives to be defined for this specific compiler and added to the standard set defined in the ANSI standard The keywords _asm and _endasm enclose a section of assembly language code in this case just one instruction GOTO label Hi Tech PIC C The Hi Tech PIC C is a professional standard compiler supplied by a company well established as a development system tool supplier Hi Tech supplies C compilers for wide range of microcontrollers on the market PIC 16 18 24 and dsPIC digital signal processors as well as Freescale 68000 based types ARM 8051 derivatives Texas Instruments MSP430 devices and other legacy products The features claimed are these e ANSI C full featured and portable e Reliable mature field proven technology e Multiple C optimization levels e An optimizing assembler e Full linker with overlaying of local variables to minimize RAM usage e Comprehensive C library with all source code provided C Compiler Comparison 231 Listing D 2 C18 Sample Source Code LED Output Using Timer Interrupt include lt p18cxxx h gt include lt timers h gt define NUMBER_OF_LEDS 8 void timer_isr void static unsigned char s_count 0 pragma code low_vector 0x18
137. ay_ms 1000 putc 254 putc 1 delay_ms 10 f Assign data to arrays sn e605 bh OSS ee ee Bs ec oe re a for n 0 n lt 10 n anum n aval aval strcepy astring Hello Display datas jcc ee ian dae thine hee A Ae oe ee oe for n 0 n lt 10 n printf d anum n putc 254 putc 192 delay_ms 10 puts astring while 1 Wait C Programming Essentials 75 and subscript placeholder anum 10 and astring 16 which instructs the compiler to allocate a suitable set of locations in RAM The variable type declaration determines how many locations per value are needed The numerical array values are initialized using a for loop a variable n which increments from 0 to 9 is used as loop counter and also as the array index value The character array values are assigned using the function strcpy string copy Its arguments are the target array name astring and the text in double quotes which is copied to the array The end of the string is automatically terminated by a zero value creating a null terminated string This allows the end of the message to be easily detected by a receiving device The numerical data are displayed on our 16x2 LCD using printf again using a for loop The string is output in a different manner the puts put string function is simpler than printf and avoids the need to output each character separately using putc However printf is stil
138. been operated Modify the program to measure the time interval between pulses from the motor sensor and display the speed in rev sec To implement this measure the pulse interval in microseconds using Timer maximum count 65 ms in Capture mode MCU clock 4 MHz This gives the time taken for half a rev in microseconds t and the speed can then be calculated in rev sec 106 2t For example if the speed is 3000 rpm probably exceeding the maximum achievable by the motor we should see 50 rev sec on the display The value of tp will then be 10 ms a count of 10 000 in Timer1 We can see from this that the minimum speed measurable is about 10 rev sec Use a suitable prescale value to extend this value to less than 1 rev sec and modify the program to improve the precision of the speed measurement to 0 1 rev sec Assignment 4 3 A temperature controller program is required for the mechatronics board that implements a cooling system The DC motor has a fan attached and the controller increases the fan speed when the temperature increases Connect up the mechatronics board for PWM control of the DC motor Write a cooling program that reads the temperature sensor and modifies the motor speed accordingly Demonstrate the application in simulation or hardware as facilities allow PIC16 C Applications and Systems 5 1 PIC16 C Application Design e Block diagram e Program outline e Debugging and testing Formal design methods reco
139. been previously installed the project can be complied and the HEX and COF files created The program is downloaded by selecting the menu Programmer Select Programmer MPLAB ICD2 Confirmation that the target is ready should appear in the output window Hit the Program Target Device button and ideally a Programming Succeeded message is returned The Release from Reset button should set the output running on the LEDs on the mechatronics board Debugging If a program does not function correctly it can be debugged in hardware using ICD2 For this exercise we run the program in debug mode anyway From the Debugger menu Select Tool MPLAB ICD2 If necessary the operating system in the ICD module is updated A reminder may be received that the ICD2 module cannot operate as a debugger and programmer at the same time An error message may be displayed at this stage indicating that the system cannot enter debug mode Resend the program and try again The output window should then show that the target system is ready The debug control panel now appears in the toolbar allowing the program to Run Stop Reset or Single Step The current execution point is displayed in the source code window Reset the program if necessary and run it The LEDs should flash in a binary sequence on the target board Stop the program and set a breakpoint at the output statement in the source code Open the watch window and display the value of n in binary It in
140. bit A complete set of operators is listed in Table 2 6 www newnespress com C Programming Essentials 53 Table 2 5 The 7 Bit ASCII Codes Figure 2 6 shows the output of a test program that carries out some sample operations High Bits Low Bits 010 011 100 101 110 111 0000 Space 0 P p 0001 1 A Q a q 0010 n 2 B R b r 0011 3 C S c s 0100 4 D T d t 0101 5 E U e u 0110 amp 6 F V f v 0111 7 G W g w 1000 8 H X h x 1001 9 l Y i y 1010 J Z j z 1011 K k 1100 lt L 1101 M m 1110 gt N A n 7 1111 O z o Del The results are shown in a watch window after running the program in MPSIM The 8 bit integer operations give the correct output while the result is in range The product of the multiplication mulbyte is clearly incorrect while the result of the integer division divbyte is truncated Floating point calculations are required in this case The floating point results show nine significant figures but only four are valid for the addition and subtraction seven for the multiplication and the division result is also correct only to seven figures 54 Part 2 Table 2 6 Arithmetic and Logical Operations Operation Operator Description Source Code Example Result Single operand Increment Add 1 to result numl 0000 0000 0000 integer 0001 Decrement Subtract 1 resul
141. bit wise operations If the result of an operation is 0 or acarry or overflow occurs this is recorded in a flag bit in the status register SFR 03 For example if a result is 0 the status register bit 2 is set The flag can then be used by a bit Test and Skip instruction to select alternate program sequences In the PIC this is implemented by the instruction following the test being skipped or not depending on the result Usually this a jump instruction GOTO or CALL which takes the program execution point to a new position or not GOTO means go to a given program memory location unconditionally CALL also means jump but store a return address so that the current sequence can be resumed when the subroutine is finished indicated by the RETURN instruction The jump destination is normally given a label such as start in the example in the source code Unlike C the program designer must allocate memory explicitly using suitable labels variables are declared using an equate directive at the top of the program to identify 94 Part 2 a GPR for that byte The register labels are then recognized by the assembler as representing a specific location Obviously only 8 bit variables can be used in assembler so care must be taken if using long values generated in the C program sections An assembler header file can allocate standard labels to the SFRs in the same way as the C header defines the control register codes The include dire
142. bolic tangent of function float x Table F 13 Make Integers Function Description Example Comment MAKE BYTE Extract a byte from mybyte Extracts byte from 16 or long integer make8 num 3 32 bit integer MAKE WORD Make a 16 bit integer myword Combine separate bytes into makel6 bytel one integer byte MAKE LONG Make a 32 bit integer mylong make32 Combine 4 bytes or two byte3 byte2 16 bit integers bytel byte0 252 Appendix F Table F 14 Type Conversions INCLUDE STDLIB H Function Description Example Comment ASC TO ASCII to float num0 Converts a decimal FLOAT conversion atof decstring number as string into float ASC TO ASCII to 8 bit integer numl Converts an integer NTEGER conversion atoi intstringl1 given as string into an 8 bit integer ASC TO ASCII to 16 bit integer num2 Converts an integer LONG conversion atol intstring2 given as string into a 6 bit integer ASC TO ASCII to 32 bit integer num3 Converts an integer 32 BIT conversion atoi32 intstring3 given as string into a 32 bit integer Table F 15 Character Test INCLUDE CTYPE H Function Description Example Comment ALPHANUMERIC Test for alphanumeric test Returns 1 if character code character isalnum acode is in ranges 0 9 A Z a z NUMBER DIGIT Test for numerical digit chara
143. but 216 Appendix B Listing B 3 List File BAR1 LST CCS PCM C Compiler Version 4 024 37533 16 Feb 07 17 05 Filename bar1 lst ROM used 59 words 1 Largest free fragment is 2048 RAM used 8 2 at main level 9 2 worst case Stack 1 locations START OF INITIALISATION kkkkkkkkkkkkkkkkkkkkkkkkkkxkXxk 0000 MOVLW 00 0001 MOVWF 0A Select Program Page 0 0002 GOTO 01B Jump to main block 0003 NOP Sapte oul ave Beer cete a ENE S K BAR1 C MPB V1 0 rotted og 2S oth a Output binary count be Be ei rd Meth SS tah lege tra ag when button pressed eft Sore Antes te oe ee LSB 50Hz Be NES opie a aad etn Simulation version ead er atone og com ANSE eta eee R E EA a E include 16F877A h odin es Foca Site atts Eas Standard Header file for the PIC16F877A device ee keto tee wha weer E ete device PIC16F877A debs Grete cS tse tate beet hats Moos list Dnt A aise ets aycegenst os ar oi 7 FUNCTION ROUTINE XK KKK KKK KKK KKK a aa A ts Ghee eve 2os ae Yas use delay clock 4000000 0004 MOVLW 22 0005 MOVWF 04 Point to delay value 0006 BCF 03 7 Select File Bank 0 1 indirect addressing 0007 MOVF 00 W Fetch delay value 0008 BTFSC 03 2 If delay value 0 0009 GOTO 018 Skip this routine 000A MOVLW 01 START 1ms DELAY LOOP void main 000B MOVWF 78 000C CLRF 77 000D DECFSZ 77 F 000E GOTO 00D OOOF
144. by generating a start bit on the data line This is followed by 4 bytes containing control address and data codes The first is the control code AO The memory chip has a factory set high address code of 0101 A This distinguishes it from other types of I C devices that may be added to the bus The next 3 bits are the hardware address 000 and the LSB is set to 0 to indicate a write operation making the low nibble 0000 This is followed by the two address bytes The high address byte is 00 and the low address increments from 0 so the test program writes only to the first 256 bytes The data byte follows which is read in from the input switches Each of these bytes must be acknowledged by the receiving device taking the data line low and the transfer is terminated by a stop bit More details on the exact data format and timing requirements may be found in the chip data sheet The simulation system allows the bus activity to be logged and displayed in the I C debug window using the virtual bus monitor instrument A time stamp the transfer codes and www newnespress com C Peripheral Interfaces 121 Table 3 8 I C Functions Operation Description Example 2C WRITE Send a single byte i2c_write outbyte I2C READ Read a received byte inbyte i2c_read I2C STOP Issue a stop command in master mode i2c_stop I2C POLL Check to see if byte received sbit i2c_poll the Start S Acknowledg
145. by the fact that the test data are retained between successive simulation runs This can be viewed if the simulation is paused and the EEPROM data window selected from the debug menu Listing 3 12 is an EEPROM test program 3 9 PIC16 C Analog Output e Waveform generator test system e Waveform test program e Waveform output In microcontroller applications analog output is not needed as often as analog input so no digital to analog converter DAC is built into the PIC MCU An external DAC is needed to generate analog output signals A serial DAC may be used to output a precision DC reference voltage or low frequency analog signal using SPI or C to transfer the data A 10 bit or 12 bit output is typically provided giving a precision of about 0 1 or 0 025 respectively However the serial data transfer is inherently slow In the demo system described here Figure 3 12 higher speed is possible with parallel output to the DAC The waveform generator circuit generates trigonometric waveforms which are displayed on the virtual digital oscilloscope The system provides 8 bit conversion giving a precision of 100 256 0 4 With a 20 MHz MCU clock the maximum output frequency is about 4kHz This is limited by the maximum rate at which the output loop can produce the instantaneous voltages that make up the waveform The DAC code is output at Port D with a variable delay to control the frequency A set of switches provides waveform selecti
146. byte mulbyte divbyte int8 incbytel decbytel combytel int8 ANDbyte ORbyte xoRbyte float numl 12 34 num2 56 78 float addfloat subfloat mulfloat divfloat incbytel bytel incbytel decbytel bytel decbytel combytel bytel addbyte bytel byte ne T E subfloat mulbyte bytel byte divfloat divbyte bytel byte addfloat num numi subfloat num nual mulfloat num nual divfloat nus nual AlDbyte bytel byte bytel byte2 bytel byte Figure 2 6 Results of Sample Arithmetic and Logic Operations in MPLAB Program Simulation Table 2 7 Conditional Operators Operation Symbol Example Equal to if a 0 b b 5 Not equal to l if a 1 b b 4 Greater than gt if a gt 2 b b 3 Less than lt if a lt 3 b b 2 Greater than or equal to gt if a gt 4 b b 1 Less than or equal to lt if a lt 5 b b 0 Sometimes a conditional test needs to combine tests on several values The tests can be compounded by using logical operators as follows AND condition if a gt b amp amp c d OR condition if a gt b c d www newnespress com 56 Part 2 a b Trug Statement Block Statement Block Condition True Figure 2 7 Comparison of a While and b Do While Loop v 2 4 PIC16 C Sequence Control e While loops e Break continue goto e If else s
147. cluding 16F877 238 Appendix D The educational compilers are designed primarily as components of training packages consisting of hardware development system compiler tutorials proprietary simulation software and so on These products should certainly be considered if a complete package is required for example by a college or university upgrading its resources The Mikroelectronika packages are oriented more toward the hobby market while the Matrix Multimedia product range is suitable for a wide range of education institutions from schools to universities The support materials provided with the Matrix Multimedia compiler are very closely tied to the training packages so no separate compiler manual is provided for example For the hobbyist and independent learner Mikro C is supported by a comprehensive and fully documented function library Compiler Directives include source files use functions parameters define oldtext newtext device name list nolist asm endasm fuses options int_xxx Program Blocks main condition statements while condition statements do statements while condition if condition statements for begin end next statements switch x case n Punctuation Comments statement Comment statement statement statement funcname argl arg2 n text y CCS C Programming Syntax Summary Include source code or header file Include library funct
148. code shown in Listing 4 13 As we see in the program only the setup function is needed which assigns the comparator inputs to Port A pins Two comparators are available and the setup used here is the same for all comparator applications using this hardware C1OUT is the bit label assigned to the Comparator 1 output bit which is tested using the if statement The LED output is then switched accordingly The pot sets the switching level and a desk lamp or flashlight was found to work as a light source The LED should go on when the light source goes off Temperature Measurement The temperature sensor on the PICDEM board has an output of 10 mV C with 500 mV 0 C Figure 4 12 For this application the TEMP pin to which the temperature sensor output is connected is linked to the first analog input RAO ANO When run the 164 Part 4 Listing 4 13 Light Switch TILSITTIITTII TTI TAIT AIA TAI TATA TAIT AIT ATTA TAIT ATTA TATA TAT TT UIGHTCON C Auto light switch uses comparator inputs on mechatronics board Pot 1 adjusted for light switching level Connect LIGHT to C1 POT1 to C1 VALINI TIA TAIT AIA TAIT AIT AIT ATT ATTA TAT TATA TATA TAT TT include 16F917 h void main setup_comparator A0_A3_A1_4A2 Setup for PICDEM board while 1 if C10OUT output_low PIN_D7 Switch off LED if light gt pot else output_high PIN_D7 Switch on LED if light lt pot PIC 1
149. crements each time the loop is executed but note that the output shows only the most significant 4 bits It therefore changes only after a count of 16 You will find that the step over function does not work This is probably because the subroutine calls in CCS C are implemented using the assembler instruction GOTO instead of CALL which the step over function is expecting This can be confirmed by opening the Disassembly Listing in the View menu 146 Part 4 Pe Cae Wow Prom Oxbugge Progemmer Tods Copre Window Hep Osu eS het SLO t peer k Rowe TEST C MPB Pirst program for testing Mechatronics Board flashes 4 LEDs include 16F917 h fuse delay clock 8000000 void main i int n 0 while 1 output_Din delay _ms i0 nee Figure 4 6 Test Program Debugging Screen The debug windows are shown in Figure 4 6 When debugging is complete clear all breakpoints and ensure that the program is working as required After the final version is downloaded and the ICD module disconnected the program should run from Reset on power up 4 2 PICDEM Liquid Crystal Display e LCD layout and connections e LCD test program e BCD count program The plain 3 5 digit parallel liquid crystal display LCD is driven directly from the MCU occupying 15 of the I O pins The usual alternative to this arrangement is to use a serial LCD which can be driven via the RS232 port This occupies only one or two pins bu
150. ctable When an input is received it must be processed and the output generated within a known time frame The point is obvious if one considers an example such as an aircraft flight control system or automobile engine controller To manage complex control system software we may need a real time operating system Real Time Operating System The principle of operation of a simple RTOS as implemented by CCS C is shown in Figure 5 7 The program is divided into separate tasks which are executed in turn A timer interrupt causes the task switching but interrupts are otherwise not used When a task is suspended its context file register state is saved and restored when it is restarted the next time around In this way multiple tasks are executed in rotation and can appear to execute PIC16 C Applications and Systems 193 START Initialize OS gt Task 1 Timer Interrupt Task 2 K Timer Interrupt Task 3 K Timer Interrupt Task N K Timer Interrupt Figure 5 7 Basic RTOS Operation simultaneously and the I O timing is more predictable More sophisticated systems incorporate task priority and implement more complex task management strategies A blank program is shown in Listing 5 5 to illustrate how CCS C implements the RTOS The MCU used is an 18F452 which is the 18 series equivalent to the 16F877 CCS C supports RTOS for only 18 series PICs and above T
151. cter test isdigit acode Returns 1 if character code is in range 0 9 character test isspace acode LOWER CASE Test for lower case test Returns 1 if character code alphanumeric islower acode is in range a z SPACE Test for space Returns 1 if character code is a space UPPER CASE Test for upper case alphanumeric test isupper acode Returns 1 if character code is in ranges A Z HEX DIGIT Test for hexadecimal digit Cest isxdigit acode Returns 1 if character code is in ranges 0 9 A F a f Test for control or space character isprint acode CONTROL test Returns 1 if character code character iscntrl acode is control code 00 1F GRAPHIC Test for printable test Returns 1 if character code character isgraph acode is graphical 21 7E PRINTABLE Test for printable test Returns 1 if character code is printable 20 7E PUNCTUATION Test for punctuation character test ispunct acode Returns 1 if character code is a punctuation code CCS C Program Function Reference 253 Table F 16 Search and Sort INCLUDE STDLIB H Function Description Example Comment BINARY SEARCH Search for given bsearch Find value k in array value in a data array k al n w compit al ofn elements of width w QUICK SORT Sort an arra
152. ction set_timer1 0 Clear Timer1 clear_interrupt INT_CCP1 Clear interrupt flag void main LEER RRR ER ERRERKERR kk kkk kkk kk kkk kkk k setup_timer_1 T1_INTERNAL Internal clock setup_ccpl1 CCP_CAPTURE_RE Capture rising edge on RC2 enable_interrupts GLOBAL Enable all interrupts enable_interrupts INT_CCP1 Enable CCP1 interrupt while 1 capture event The captured value is copied automatically into a variable called CCP_1 The simulation of this program is shown in Figure 3 6 When the program is run with the 100 Hz signal input a count of 9963 us is captured error 0 4 This shows that some allowance may be needed for the software overhead associated with the capture process and adjustment made to correct the result obtained C Peripheral Interfaces 113 period MPLAB IDE v7 52 a27 Fle Edt View Project Debugger Programmer Tools Configure Window Help OS MA GAR des VT SRBBO 2H rueBRPOR ee PERIOD C MPB 11 4 07 Demo period measurement include 16F877A h int16 count int_ccpl void isr_ccpl set_timerl 0 clear_interrupt INT_CCP1 void main setup_timer_1 T1_INTERNAL setup_ccpl CCP_CAPTURE_RE Figure 3 6 Capture Mode Used to Measure Input Period 3 4 PIC16 C UART Serial Link e RS232 port functions e Simulation with virtual terminal A basic serial link is provided by the UART We have already seen that any pair
153. ctions RESET_CPU SLEEP RESTART _CAUSE Constants returned from RESTART_CAUSE are define WD define WD define MCLR_FROM_S define NORMAL POWER_UP 24 Watchdog timer has woken MCU from sleep Watchdog timer has caused reset MCU has been woken by reset input Normal power on reset has occurred 11 111 111 111 111 11 1 11 1 11 1 111 111 11 1 111 11111 1 11 111 11 11 1 1 Timer 0 AKA RTCC Functions SETUP_COUNTERS or SETUP_TIMERO SET_TIMERO or SET_RTCC GET_TIMERO or GET_RTCC ETUP_TIMERO are Use instruction clock Use TOCKI rising edge Use TOCKI falling edge No prescale Prescale divide by 2 Prescale divide by 4 C Programming Essentials 81 ai Ri ne BA nn RI define define define define define define CCa PECs CG REC LEC LEG DIV_8 DIV_16 DIV_32 DIV_64 DIV_128 DIV_256 NanU PWD RI BIT 0 define RTCC_8_ Constants used for S constants for the is the 2nd param ETUP_COUNT t param and the following for Prescale Prescale Prescale Prescale Prescale Prescale ERS divide divide divide divide divide divide by by by by by by 16 32 64 128 256 are the above TITTITTTTTTIT TTT TATA TT AAT TTT ATTA TTA TTT TTT TATA TTT TTT TIT WOT Watch Dog Timer Functions S
154. ctive is the same in C and assembler and can be used to include assembler header library and user source code There are only 35 core instructions in the 16FXXX instruction set This reduced instruction set increases the program execution speed Additional special instructions are available to compensate for the limited instruction set these are basically predefined macros A macro is a code sequence that can be predefined and given its own name then inserted by the assembler when invoked by name User defined macros may also be created as required Therefore if direct control of the MCU registers and instruction sequence is required for any reason or the speed of execution is critical the C programmer can always revert to assembler code Since most microcontroller application designers are familiar with assembly language anyway including assembler blocks typically requires little additional learning time Assessment 2 5 points each total 100 1 List the syntax features that a minimal C program must contain if compiled for the PIC16F877A MCU 2 List the steps required to create and test a C program for a PIC MCU prior to downloading to hardware 3 Write a C statement that outputs the 8 bit value 64 to Port C Write an alternative 1 bit output statement that has the same effect assuming all the port bits are initially 0 4 Describe briefly the difference between a WHILE loop a DO WHILE loop and a FOR loop 5 Describe t
155. culate PWM duty cycle Read LightIn If LightIn out of range Indicate fault Disable outputs Wait for reset If LightIn gt Sunlit Modify FanPWM duty cycle Add offset to PWM duty cycle Heat1 Heat2 FanPWM FaniInt Fault Reset Fani EN RD1 RD2 RD6 RC5 RD5 RD7 on off on off 0 255 0 255 0 1 0 1 0 1 C Mechatronics Applications 171 Enable fan Disable Heaters Wait 5s for fan to start If speed 0 Indicate fault Disable outputs Wait for reset Else enable RunOK Always 4 7 PICDEM Board Simulation e Mechatronics board simulation schematic e Mechatronics board circuit operation e Mechatronics board applications A simulation version of the PICDEM mechatronics board created in Proteus VSM is provided on the support Web site www picmicros org uk The ISIS schematic is shown in Figure 4 14 The circuit has been organized into functional blocks and some hardware features are not included to simplify the schematic For example generic drive FETs were used for compactness on the schematic rather than the specific devices It was not necessary to include the circuit of the optical interrupter interface since the DC motor and pulse encoder are modeled in VSM as one component The RS232 interface is designed to work primarily with a terminal software module provided with the PICDEM kit and therefore also was not included Components such as decoupling and filt
156. d the Intel 8051 was developed alongside the early Intel PC processors such as the 8086 This device dominated the field for some time others emerged only slowly mainly in the form of complex processors for applications such as engine management systems These devices were relatively expensive so they were justified only in high value products The potential of microcontrollers seems to have been realized only slowly The development of flash ROM helped open up the market and Microchip was among the first to take advantage The cheap and reprogrammable PIC16F84 became the most widely known rapidly becoming the number one device for students and hobbyists On the back of this success the Microchip product range rapidly developed and diversified The supporting development system MPLAB was distributed free which helped the PIC to dominate the low end market Flash ROM is one of the technical developments that made learning about microsystems easier and more interesting Interactive circuit design software is another The whole design process is now much more transparent so that working systems are more quickly achievable by the beginner Low cost in circuit debugging is another technique that helps get the final hardware up and running quickly with only a modest expenditure on development tools PIC Microcontroller Systems 3 MCU Features The range of microcontrollers now available developed because the features of the MCU used in an
157. d CCS C diverge Remember however that the general language syntax must conform to the ANSI standard Listing D 1 shows a simple LED flasher program Listing D 1 C18 Sample Source Code LED Flasher include lt p18cxxx h gt MCU header file eEeE void delay void Delay function eeKKKK unsigned int i for i 0 i lt 10000 i void main void Main Program kREEKKEK TRISB 0 Port B output baie while 1 Loop always RY PORTB 0 Reset the LEDs aed delay Delay to see change bay PORTB 0x5A Light the LEDs af delay Delay to see change RY 230 Appendix D The MCU header file is included in the same way as in CCS C and the delay routine uses standard syntax The main difference evident is that the port registers are addressed directly by assigning a value to the data direction register e g TRISB 0 and the output data register e g PORTB 0x5A In CCS C a function is used output_B 0 The C18 syntax is arguably simpler Listing D 2 a C18 program using interrupts illustrates some other differences As in many PIC C compilers direct access to the register control bits is used for example in the statement INTCONbits TMROIF 0 which resets the timer interrupt flag This requires knowledge of the internal architecture which makes the programming more difficult CCS C sensibly avoids the need for such direct access The timer setup st
158. d a new project created with the same name A workspace window appears with file project folders named Source Files Header Files and Other Files Open a new source window type in the program header comment at the top of the program as shown in Listing 1 1 and save the file as PROJNAME C in the project folder Type the rest of the program in and save it The source code must now be attached to the project by right clicking on Source Files workspace folder to open the add file dialog Note in the source code a statement include 16F877A h This defines the specific chip for which the program is created and refers to a header file supplied with the compiler This file must be included because it holds information about the chip register addresses labeling and so on it can be viewed in any text editor and is listed in full in Section 2 8 The file should be copied from the Devices folder in the CCS C program file folder set into the project folder It can then be attached to this project by right clicking on the Header Files folder We are now ready to compile the program by clicking on the Compile button in the MPLAB main toolbar The compiler execution dialog briefly appears and ideally a build succeeded message is displayed The program can now be tested in simulation mode by selecting Debugger Select Tool MPLAB SIM This brings up a control panel in the main toolbar Press Reset and a green arrow indicates the execution po
159. d for only highly complex specialist systems or where a low cost standard board such as the PC motherboard can be easily adapted The discrete microprocessor does however allow multiprocessor systems to be designed that typically use shared hardware resources especially memory Current standard processors typically incorporate features to support multiprocessor operation and the dual core processor is currently becoming standard in PCs The SoC takes the concept of the microcontroller to the next level It is in effect a configurable microcontroller where the designer has control over the internal 196 Part 5 arrangement of the hardware elements Using a dedicated design system the processor core is selected and the required memory and peripherals added These hardware elements are supported by corresponding standard drivers provided as part of the package With a complex interface such as USB for example the provision of a standard protocol stack software layers not a hardware stack is essential The design can be fully tested in software in the same way that a PIC program can be tested in MPLAB Only when finally verified is the design fabricated by the hardware supplier If a design is to be created from scratch then the most appropriate type of system may be selected from the three main options listed previously However this choice is unlikely to occur in isolation factors such as the previous experience of the design team
160. de 16F877A h use delay clock 4000000 use rs232 baud 9600 xmit PIN_DO rcv PIN_D1 Define speed and pins void main char acap A Test data delay_ms 1000 Wait for LCD to wake up putc 254 putc 1 Home cursor delay_ms 10 Wait for LCD to finish while 1 putc acap Send test character putc 254 putc 192 delay_ms 10 Move to second row printf ASCII c CHAR d acap acap Send test data again while 1 Table 2 8 Essential Control Codes for Serial 2x16 LCD Code Effect 254 Switch to control mode followed by 00 Home to start of row 1 01 Clear screen 192 Go to start of row 2 Listing 2 16 shows the program FLOAT C which illustrates how different variable types are displayed as well as showing the range of each type Each variable type is output in turn to the display The general form of the format code is nt where n is the number of significant figures to be displayed and t is the output variable type The number of 68 Part 2 Table 2 9 Output Format Codes Code Displays sd Signed integer eu Unsigned integer SLu Long unsigned integer 16 or 32 bits SLs Long signed integer 16 or 32 bits SG Rounded decimal float use decimal formatting Sf Truncated decimal float use decimal formatting Se Exponential form of float Sw Unsigned integer with decimal point inserted use decim
161. de Some students teachers and hobbyists may wish to skip a detailed study of assembler coding and go straight to C which is generally simpler and more powerful It is therefore timely to produce a text that does not assume detailed knowledge of assembler and introduces C as gently as possible Although several C programming books for microcontrollers are on the market many are too advanced for the C beginner and distract the learner with undesirable detail in the early stages This text introduces embedded programming techniques using the simplest possible programs with on screen fully interactive circuit simulation to demonstrate a range of basic techniques which can then be applied to your own projects The emphasis is on simple working programs for each topic with hardware block diagrams to clarify system operation full circuit schematics simulation screenshots and source code listings as well as working downloads of all examples Students in college courses and design engineers can document their projects to a high standard using these techniques Each part concludes with a complete set of self assessment questions and assignments designed to complete the learning package An additional feature of this book is the use of Proteus VSM virtual system modeling The schematic capture component ISIS allows a circuit diagram to be created using an extensive library of active components The program is attached to the microcontroller and
162. de of operation of these registers are as counters for external events or timers using the internal clock Additional registers are used to provide Capture Compare and Pulse Width Modulation PWM modes The CCS timer function set is shown in Table 3 5 Counter Timer Operation A counter timer register consists of a set of bistable stages flip flops connected in cascade 8 16 or 32 bits When used as a counter a pulse train fed to its least significant bit LSB causes the output of that stage to toggle at half the input frequency This is fed to the next significant bit which toggles at half that rate and so on An 8 bit counter thus C Peripheral Interfaces 109 Table 3 5 Timer Functions Action Description Example TIMERX SETUP Set up the timer mode setup_timer0 RTCC_ INTERNAL RTCC_DIV_8 TIMERX READ Read a timer register 8 or 16 bits count0O get_timer0 TIMERX WRITE Preload a timer register 8 or 16 bits set_timer0 126 CCPX SETUP Select PWM capture or compare setup_ccpl ccp_pwm mode PWMX DUTY Set PWM duty cycle set_pwml_duty 512 counts up from 0x00 to 0OxFF 255 before rolling over to 0 again overflow The binary count records the number of clock pulses input at the LSB In the 877 Timer0 is an 8 bit register that can count pulses at RA4 for this purpose the input is called TOCKI Timer0 clock input Timer is a 16 bit register that can count up to
163. digital converter 15 comparator 15 16 digital I O 12 13 interrupts 16 18 parallel slave port operation 16 timers 13 15 program and debug 26 30 debugging 29 30 design package 30 programming 27 8 serial interfaces 18 22 interintegrated circuit bus 21 2 SPI bus 20 21 USART 19 20 Index 275 PIC16C 35 analog input 99 analog setup 99 100 101 voltage measurement 100 3 analog output 127 32 application design 179 debugging and testing 180 2 hardware design 179 80 software design 180 181 applications and systems 179 data logger system 184 9 design 179 82 operating systems 189 94 system design 195 200 temperature controller 182 4 185 assembler routines 86 assembler block 88 92 PIC assembly language 92 4 program compilation 87 8 compiler directives 77 header file 78 86 program directives 78 data logger system 184 BASE board 186 9 program outline 188 189 data operations 47 assignment operations 52 4 55 conditional operations 54 5 variable types 47 52 data types 73 arrays 74 5 enumeration 77 indirect addressing operators 75 7 EEPROM interface 126 7 128 functions and structure 60 arguments 62 3 global and local variables 63 4 65 program structure 60 2 hardware timers 108 capture mode 111 13 compare mode 111 counter timer operation 108 9 PWM mode 109 11 PC serial bus 118 21 input and output 64 keypad and calculator 68 73 276 Index PIC16 C Continued RS232 serial data 64 65 serial LCD 65 8 69 interr
164. done portb adresl Display low byte porta adresh 2 Display high bits The application programming can be implemented using a choice of assembler or C Matrix also offers a proprietary flowchart based programming system Flowcode The program is constructed using flowchart blocks which are automatically converted to C and hence to assembler and machine code The C syntax used is illustrated in Listing D S a simple program to read an analog input and display the result As in many C compilers for PIC the control registers are loaded directly and no special functions are used for peripheral access The programming system is described via a tutorial which is included with the compiler so no separate reference manual is provided Summary of C Compilers The features of the C compilers for the PIC 16 series MCUs outlined in this appendix are compared in Table D 1 We are particularly interested in using the 16F877 our reference device which is used in the demo applications in the main part of this book The compilers have been divided into commercial and educational categories C Compiler Comparison 237 Table D 1 Comparison of C Compilers for PIC 16 Series M Microchip C18 Hi Tech C CCS C Mikro C MM C URL microchip htsoft com ccsinfo mikroe com matrixmultimedia com com com Primary Commercial Commercial Both Educational Educational market M
165. e A and Stop P bits are detected as they occur In addition the memory contents can be displayed to confirm the test data and which locations have been written When the memory content window is opened we see that it retains the data from previous runs of the simulation representing the nonvolatile nature of the data store To see the data change a new code must be set on the switches for each run The C functions are summarized in Table 3 8 3 7 PIC16 C Parallel and Serial Interfaces e PSP functions and test system e Comparison of parallel and serial links The parallel slave port PSP allows an external controller to initiate an 8 bit data exchange with the PIC MCU This method of data exchange is compared with the serial ports Parallel Slave Port In the example in Figure 3 10 a master 877 is feeding data to a slave chip of the same type Arbitrary data are set on the DIP switch at Port B of the master The internal pull ups available on these pins are activated in the master program to avoid the need for external resistors on the switches The test data are transferred to Port C and presented to the slave Port C pins Listing 3 10 The slave port is already enabled via EO cS not 122 Part 3 13_ OSC1 CL
166. e Create a new design file and save it as BAR1 DSN in a project folder called BAR1 which is accessible from Proteus and MPLAB To start the schematic the Component button should be clicked to enable the Devices mode in the object window The Pick Devices button P at the head of the Object Selector panel gives access to the device libraries Figure A 3 The category Microprocessor ICs has a subcategory PIC 16 Family from which the PIC 16F877 can be selected it then appears in the device list www newnespress com 206 Appendix A 5S bar ISIS Professional O68 8G 68 Bs QQQQ 9 BR SEBR RYE PICTE Microcontroller 7688 code 258 data Ports A B 1xTimers PICIE Microcormoller 7688 code 258 data Ports A B 1xTimers PIC16 Microcontroller 7688 code 248 data Ports A C 1xTimers PIC16 Microcortnoller 7688 code 248 data Ports AC IxTimers PICIG Microcorinoler 15368 code 258 data Ports A B 1xTimers PICTE Microcontroller 15368 code 258 data Ports A B IxTimers PICIE Microcoemoller 20728 code 728 data Ports AC 1xTimers os PICT6 Microcortrolier 30728 code 728 data Ports AC IxTimers RES PIC16 Microcontroller 10248 code 368 data Ports AB 1xTimers RESPACK 8 T PICTE Microcormoller 2kB code 1286 data Ports A C 1xCOP Timers PICT6 Microcontroller 4kB code 1928 data Ports A C DOOP Timers PIC1E Microcontroller 2kB code 1288 data Ports AE 1xCOP PSP XTi PICTE Microcontroller 4kB code
167. e merits of a serial alphanumeric LCD module and the DMM display used in the PICDEM mechatronics board 16 Discuss briefly the factors that affect power consumption in an embedded system and how to evaluate it 17 Explain the advantages of using C for embedded applications 10 points Assignments 5 To undertake these assignments install Microchip MPLAB www microchip com Labcenter ISIS Lite www proteuslite com and CCS C Lite www ccsinfo com Application files may be downloaded from www picmicros org uk Run the applications in MPLAB with Proteus VSM selected as the debug tool Display the animated schematic in VSM viewer with the application COF file attached to the MCU see the appendices for details Assignment 5 1 Download the project TEMCON and check that it runs correctly in MPLAB with Proteus VSM viewer Modify the program to display warning messages when the temperature is more that 3 C above the upper switching level TOO HOT or more that 3 C below the lower switching level TOO COLD Assignment 5 2 Design a controller for a small hot and cold drinks machine aimed at the domestic market Write a specification based on your own understanding of the typical requirements of such a machine draw a block diagram showing the interfacing required and outline a control program which can be implemented in C Predict the input output and memory requirements and select a PIC microcontroller www microchip com which prov
168. e of the stepper motor is that it provides position control without the feedback required by a DC motor It has stator windings distributed around a cylindrical rotor which has permanent or induced magnetic poles The windings operate in groups to move the rotor by a fraction of a revolution at a time Figure 4 8 C Mechatronics Applications 157 Figure 4 9 Bipolar Permanent Magnet Stepper Motor with Two Winding sets swe RD7 Pi m Drivel K EEE Direction COPD EWM c RD6 P2 ae gt contro c Drive 2 rand sw3 PIC logic 9 16F917 RDS P3 linked for Faster full bridge Red CCP2 PWM3 drive Drives K 3 sw3 m operation RD4 P4 Winding Slower j Mickel m Drive4 K Figure 4 10 Stepper Motor Test System Connections Construction The small stepper motor on the mechatronics board is an inexpensive permanent magnet PM type giving 7 5 degrees per step 48 steps per revolution It can also be moved in half steps by suitable operation of the windings or even smaller steps microstepping by suitable modulation of the winding current The motor has two bipolar windings which means the current is reversed to change the polarity of the stator pole The coils energize two rings of poles creating alternating north and south poles which interact with the permanent rotor poles Figure 4 9 Representative windings are shown F
169. e output to represent the heater load The motor is operated by drive 4 with the PWM input to the bridge providing speed control All these Table 4 7 PICDEM Board I O Allocation for Temperature Controller Excluding LCD Pin Label Type Board Description RAO Tempin Analog in TEMP Range 0 50 C 500 1000 mV RA1 Lightin Analog in LIGHT Range 0 5 V needs calibration RA2 SetTemp Analog in POT1 Range 0 5 1 00V set target temp RA3 Vref Analog in POT2 Adjusted to 1 024V RA5 Startin Digital in SW2 Active low push button start system RA6 Stopin Digital in sw3 Active low push button shut down RE3 Reset Digital in sw Active low hard wired MCLR RD4 RunOK Digital out DO Active high status indicator LED RD5 Fault Digital out D1 Active high status indicator LED RD6 FanPWM Digital out PWM4 Active high DC motor DRIVE 4 RD7 FanEn Digital out N4 Active high DC motor drive enable RC5 FaniInt Digital in CCP1 DC motor pulse feedback OPT INT RD1 Heatl Digital out N1 Active high heater 1 on DRIVE 1 RD2 Heat2 Digital out N2 Active high heater 2 on DRIVE 2 C Mechatronics Applications 169 loads are controlled at the N drive inputs which operate single ended in sink mode since the current drive is needed in only one direction The P gates can remain disabled The fan speed is controlled using a CCP module in capture mode This allows low speeds to be m
170. e system which can be adapted to a range of applications the BASE board Again a full simulation version is provided for testing and further development work This is followed by a section on operating systems which compares three program design options a polling loop interrupt driven systems and real time operating systems Consideration of criteria for the final selection of the MCU for a given application and some general design points follow Three appendices A B and C cover hardware design using ISIS schematic capture software design using CCS C and system testing using Proteus VSM These topics are separated from the main body of the book as they are related more to specific products Taken together MPLAB CCS C and Proteus VSM constitute a complete learning design package but using them effectively requires careful study of product specific tutorials VSM in particular has comprehensive well designed help files and it is therefore unnecessary to duplicate that material here Furthermore as with all good design tools VSM evolves very quickly so a detailed tutorial quickly becomes outdated Appendix D compares alternative compilers and application development areas are identified that would suit each one Appendix E provides a summary of CCS C syntax Introduction xix requirements and Appendix F contains a list of the CCS C library functions provided with the compiler organized in functional groups for ease of reference
171. easured accurately The temperature sensor is calibrated at 10 mV C with an operating accuracy of 2 C and offset of 500 mV at 0 C The temperature range is 0 50 C so the sensing range is 500 1000 mV If the second pot is used to provide a reference voltage of 1 024 V the 10 bit conversion factor is 1 mV per bit and the temperature is easily calculated in the program by subtracting 500 from the input The light sensor needs to be tested to establish the output level when exposed to sunlight and a threshold value incorporated into the program so that the cooling boost cuts in at an appropriate level When testing the system hot and cold air could be applied to the temperature sensor to check basic functionality but the set temperature input provides a more convenient test input If the temperature at the sensor is constant room temperature adjusting the set input above and below this value has the same effect as the temperature falling and rising If the application functions correctly when the set temperature is adjusted to the actual room temperature neither the heater nor motor output is on If the set value is increased meaning the input temperature is too low one heater comes on If increased further the other heater comes on If the set value is decreased the input appears too high and the fan comes on As the set value is further decreased the fan speeds up When the set value is returned to room temperature all outputs
172. ecting factor of approximately 1 2 C could be implemented by simply adding 1 to the ADC result to give a display to the nearest whole degree Note that the automatic type conversion incorporated into the complier simplifies the arithmetic significantly The type is changed automatically while preserving the value as far as is possible in the new format Therefore a decimal is truncated to an integer by simple assignment of the value from a float to integer variable 4 6 PICDEM Temperature Controller e Specification of temperature controller e Input and output allocation e Program outline The PICDEM mechatronics board will now be used as the hardware platform for a temperature controller Using a ready made board eliminates the need for detailed hardware design and should be considered if a suitable product is available at a reasonable cost Specification A temperature controller is required to control a greenhouse or similar outdoor enclosure at a temperature of 25 30 C using electric heaters and a cooling fan C Mechatronics Applications 167 Set Temp gt lt Temp Sensor ADC Vref gt K Light Sensor Stat y PICDEM Mechatronics Fan Stop Board e Reset Pulse PIC 16F917 Sensor 3 5 LCD K ese Figure 4 13 Block Diagram of the Temperature Controller 1 Overall function Maintain target temperature within 2 C displaying it on the LCD If the
173. ection After selection from the object list a component can be placed with a left click on the schematic highlighted red with a right click and removed by right clicking again Components are connected together by clicking on the pins in the Component mode Wires can be connected but space on the connecting wire must be allowed between pins Always connect in line with a pin and check that a dot appears to confirm that a junction between pins has been created The Terminal button brings up the TERMINAL list The Ground and Power pins can then be placed The Power pin automatically adopts the Vaq of the MCU 5V The Overview window allows the schematic to be recentered and displays the components The schematic can also be zoomed and centered using the mouse wheel www newnespress com Hardware Design Using ISIS Schematic Capture 207 Components can be oriented or flipped using the rotation and reflection buttons and groups of selected components moved or copied using the Tagged Object edit buttons Each editing feature should be explored by reference to the Proteus help files and practical experiment The clock circuit and power supplies are implicit in the microcontroller model so it is not actually necessary to include the external clock components at this stage However they must be added before a circuit layout is generated in ARES The simulation clock rate for the MCU should be set in the component properties dialog when the CO
174. ection 2 6 in connection with the calculator demo application Listing 5 4 Program Outline for Data Logger LOGGER Initialize Delays Analogue inputs UART port I2C port Interrupts Main Set logging interval Select active analogue inputs Enable interrupts Wait Interrupt Routines Timeout Restart timer Read selected analogue inputs Store in external EEPROM Display channels and input voltages Return from interrupt Zerokey Disable timer Display Logging Stopped If Starkey Restart logging If Hashkey Send data via RS232 Display Sending data Return from interrupt PIC16 C Applications and Systems 189 The parallel LCD is used to display status messages and data as they are sampled It is useful to compare it with the serial LCD described previously as parallel access is generally faster particularly when bit maps are used for graphics in more sophisticated applications The 8 bit ASCII and control codes must be sent as 4 bit nibbles from RD4 7 with RD1 acting as the register select RS input and RD2 generating the data strobe E More details are provided on driving the parallel LCD in Interfacing PIC Microcontrollers by the author Alternatively the manufacturer s data sheet can be consulted for the necessary control codes and timing information Program Outline As can be seen in the program outline Listing 5 4 the application is largely interrupt driven The timer interrupt
175. ections gt PICKit 2 Programmer Fle Device Family Programmer Tools Help Midrange Configuration Device PICIEFESO Configuration OFES User IDs FF FF FF FF Checksum 1506 Hex file sucessfully imported AN MICROCHIP CT SO ov rice Dan Program Memory E Enabled Hex Only Source CU ook Apps PICKER progs ikat kitl hex SO z E Enabled Hex Ony v Write Device 00 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FFA 10 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF Export Hex File 20 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF iS 30 FF FF FF FF Fe re re re re re re re re re rev PICKit 2 Figure 1 19 PICkit2 Programmer Dialog Once the hardware is connected up and the programmer drivers loaded the programming utility window Figure 1 19 can be opened by running PICkit2 exe file selected from the Programmer menu The hex file created by the compiler is imported via the file menu and downloaded using the write button The target program is run by checking the On box www newnespress com PIC Microcontroller Systems 29 Figure 1 20 Microchip ICD2 Module Host PC MPLAB PIC MCU Development IEDs Target nterface System 6 WAY System C Compiler connector Figure 1 21 ICD2 Program and Debug System Debugging If in circuit debugging is required the Microchip MPLAB ICD2 in circuit debugger Figures 1 20 and 1 21 is recommended This allows the application program to be
176. ed in C they are stored in the GPRs starting at address 0020h The file registers are divided into four blocks register banks 0 to 3 The SFRs are located at the low addresses in each RAM bank Some registers are addressable across the bank boundaries for example the status register can be accessed in all blocks at the corresponding address in each bank Others are addressable in only a specific page for example Port A data register Some register addresses are not physically implemented Since some registers are accessible in multiple banks bank switching can be minimized by the compiler when assembling the machine code thus saving program code space and execution time For full details of the file register set see the MCU data sheet The program counter uses two 8 bit registers to store a 13 bit program memory address Only the low byte at address 002h is directly addressable The status register 003h records results from ALU arithmetic and logic unit operations such as zero and carry borrow The indirect and file select registers are used for indexed addressing of the GPRs Timer0 is the timer counter register available in all PIC MCUs while Timer1 and Timer2 registers are in the peripheral block The port registers are located in Bank 0 at addresses 05h Port A to 09h Port E with the data direction register for each at the corresponding location in bank 1 We can see that a total of 80 16 80 96 96 368 GPRs are available fo
177. ed to an MCU serial output if the value of incode is 0x41 Outline how to structure a program using interrupts that can carry on some other task while the serial data are transferred to and from the UART and explain why this might be useful By reference to Section 1 4 explain briefly how the hardware and master program would be modified if more than one slave sender were in the SPI system shown in Figure 3 8 List the sequence of I C statements to write the data byte 0xAA to address 0x01FF in the serial memory chip in the system shown in Figure 3 9 Draw a block diagram showing how to connect two PIC MCUs using an I C link 134 Part 3 15 16 17 18 19 20 Describe the sequence of operations required to write a byte to the parallel slave port of the PIC MCU and to force the slave MCU to read the data in immediately By reference to Table 3 10 select a serial link that connects numerous PIC MCUs to a master controller using the minimum number of wires and explain briefly why this not the fastest method to read from a serial peripheral Select from Table 3 10 the most suitable communication link for each of these applications one for each method a An interface to a conventional memory chip with 8 bit data access b A robot control system with one master MCU and six motor control slaves c An MCU data logger uploading to a PC spreadsheet d A multiprocessor system with shared serial memory
178. een tested in simulation mode the full ICD debugging interface is not needed PICDEM Hardware The block diagram Figure 4 2 shows the main parts of the mechatronics board It is built around a PIC 16F917 which is similar to the 16F877A but incorporates an LCD driver module which allows a plain 3 5 digit display to be operated with no additional interfacing The MCU internal clock runs at 8 MHz giving a 0 5 s instruction cycle The main output devices are a small DC motor and a stepper motor These are operated from a set of four current driver FETs which can sink or source current These allow either motor to be driven in both directions when connected as a full bridge driver Input tactile push switches and output LEDs are provided for simple test programs mode selection and 138 Part 4 Tyee Figure 4 1 PICDEM Mechatronics Board by permission of Microchip Inc status indication An RS232 serial port for exchanging data with the PC host is fitted which requires a suitable terminal program running on the PC A temperature sensor is fitted which outputs 10 mV C with OC giving 500 mV Therefore at 20 C the output will be 500 20 X 10 700 mV This voltage can be fed to an ADC input or comparator input on the MCU A light sensor is also available giving an output in the range 0 5 V Two pots giving 0 5 V can be used as reference inputs for the analog sensors or as test inputs for analog applications The mechatronic
179. egister 07 pin 7 INPUT_x 80 Part 2 define define define define define define define define define define define define define define define define define define define define define define define define define define define define PIN _DO 64 PIN D1 65 PIN D2 66 PIN _D3 67 PIN _D4 68 PIN_D5 69 PIN _D6 70 PIN_D7 71 PIN_EO 72 PIN_E1 73 PIN_E2 74 FALSE 0 TRUE BYTE BOO 1 int getc getch fgetc getch getchar getch putc putchar fputc putchar fgets gets fputs puts Timer 0 RI BA RI ki BA RI ree ree rCe PECS LEAN short int FROM_SLEEP 0 TIMEOUT 8 EEP 16 Constants used for S CC_INTERNAL 0 EC EXT_L_1 TO_H 32 EXT_H_1 DIV_1 DIV_2 DIV_4 rTO_L 48 8 0 1 Register 08 pin 0 8 8 0 64 Register 08 pin 1 etc Register 08 pin 2 Register 08 pin Register 08 pin Register 08 pin Register 08 pin Register 08 pin NTHAW BW Register 09 pin 0 9 8 0 72 Register 09 pin 1 etc Register 09 pin 2 TITTTTTTTATATATATAT ATA TATA TAA AAA AAA TATA AAA AAAI AAAI Useful defines Logical state 0 Logical state 1 8 bit value 11 bit value Alternate names for identical functions TIITITITATITI TAA TATA ATI TAA ATTA TAA TTT AAA TAA ITAA AAT Control Control Fun
180. eling off as the production volume increases Hardware Design Taking the hardware design criteria in turn we can consider some of the relevant factors in getting started with a design assuming an agreed on initial specification Having said this it is useful to know how much flexibility is allowed in meeting the specification 198 Part 5 1200 1000 800 600 Cost per board 0 5 10 15 20 25 30 35 Number of boards Figure 5 8 Production Cost because a disproportionate cost might be involved It may be acceptable to reduce the performance to reduce costs for example reducing the precision of analog measurements or the frequency range of a signal output The cost of the microcontroller tends to increase with the number of I O pins so it is probably a good idea to look for ways to reduce the pin count One example we saw in previous sections is to use a serial LCD instead of a parallel one The serial type requires only 1 output while the parallel LCD seen earlier needs 7 or possibly 11 if 8 bit data are used Certainly the serial interface should be considered the default choice and the parallel used only if high speed access to the display is needed The serial link can also be physically longer Serial access sensors are becoming more common where the data are sent to the MCU in serial form rather than as an analog signal We saw that any pin can be used as an RS232 port because CCS C provides a d
181. ematic can be derived from it Software Design The application program can be designed using various methods A flowchart shows the overall program sequence in a visual manner and is good for illustrating simple program sequences However for C programs some form of structured pseudocode is recommended where the main program is outlined as a text file which can then be converted directly to source code Examples are again found throughout this book the general content is described in Listing 5 1 After the application program source code has been created in the MPLAB text editor it can be compiled to generate the project file set This includes the MCU machine code HEX file and the COF file which incorporates the hex file with additional debugging information It is necessary to have all the project files in the same folder making copies of the resource files as necessary All applications need an MCU header file such as 16F877A H The application source code MCU header file and any other files to be included or used must be attached to the project in the project file window The application can then be built and the HEX machine code file produced This is downloaded to the target system to operate the application in hardware Application Debugging and Testing The application program is tested and debugged in several stages The main types of errors and the tools for detecting them are outlined next PIC16 C Applications and Syst
182. ems 181 Listing 5 1 General Control Program Outline PROGNAME C 0 111 11 1 1 11107 Program header information Author date version etc Include MCU header file Include function library files Include user source files Use function library files Define constants Declare global variables Declare function prototypes Main block 1 1 1 70 Initialization sequence Initialization function calls etc Main loop Sequences Function calls level 1 etc and repeat Function block 1 Initialization sequence Process sequences Function calls level 2 etc and return Syntax errors are mistakes in the source code such as spelling and punctuation errors incorrect labels and so on which cause an error message to be generated by the compiler These appear in a separate error window with the error type and line number indicated so that it can be corrected in the edit window When the program is successfully compiled it can be tested for correct function in the target hardware so that any logical errors can be identified However it is preferable to test it in software simulation mode first as it is quicker and easier to identify errors in the program sequence Two simulation methods are available here MPSIM and Proteus VSM MPSIM is the simulator provided with MPLAB It allows the program source code to be run stopped and stepped and breakpoints set
183. er Comparison The intention of this book is to introduce C programming for all microcontrollers However particular products have to be selected to act as examples When the basics have been explained using one particular combination of MCU compiler and development system others can be considered The CCS C compiler was selected for this book principally because it has an extensive library of peripheral driver routines is reasonably inexpensive and is recognized by Microchip and Labcenter as a preferred compiler However several other suitable compilers are available at the time of this writing so it would be useful to see how they compare The following products have been selected but bear in mind that in the rapidly moving microcontroller market significant changes probably have occurred by the time you read this e Microchip C18 e HiTech PIC C e Mikroelektronika C e Matrix Multimedia C The first two are professional compilers which would tend to be used by more experienced engineers The second two are aimed at the educational market and include more user friendly features to help the beginner Other PIC C compilers are available that are not considered here They are typically supplied by companies that produce development tools for a range of different processors which could suit application developers who use a range of MCU types They do not provide the range of library functions considered essential here 228 Appendix
184. erial gt 1csPCLK TX Serial Link Programming RAO ANO LCD gt 3 5 Digit RA1 AN1 Display RA3 AN3 Available _ ____ valable KQ RAT RD2 CC Available I O gt RAS AN4 P2 Drive Supply LEDs i J14 x8 eeeeoeooee Source Enable Px gt Half Motor Control PWMx gt Bridge gt Winding P9 Sink Enable Nx gt Driver O 1A P10 Step 1 2 3 4 P9 p1 4 A Motor J P10 P12 Fault P11 Motor Shutdown Current P12 Winding Sense Currents J15 P9 P10 Fault cI Current gt Shutdown Optical F ai Sense Interrupter an Circuit 5 Curent 2 pulses rev J7 Sense 0 1V Figure 4 2 Block Diagram of PICDEM Mechatronics Board 140 Part 4 Ten eae STEPPER MOTOR pi e fos E ee o ON e it ne i oft sn d ma Ia v Re RA C24 TEMP SENSOR SERIAL RSTI 9 12V0C GND O SERN or Bae ex og FT capo p reign 1 vemm o p tent 7 ore M Rio 11 Ocagi PICDEM Mechatronics a xo De D1 D2 D3 D4 D5 D6 D7 EE psa eae m oF T26 j PWR ON POTI i EN F ch ao BBE SBS gn o EE GGI CIII I I rn DRIVE er N B ia Rat mmer BRUSHED DC MOTOR p C25 C34 c12 I vo aes ie 1 el d a J res Mes ogue A tata ys asus 3 Ful Bridas e Mc
185. ering are used only where essential for accurate circuit modeling The overcurrent sensing circuit has a simulated input added because variations in the motor loading cannot be represented this also allows the operation of this part of the circuit to be tested independently The back emf from the DC motor can be modeled by a voltage source or simple pot if required The component numbering is the same as the hardware wherever possible The circuit connections between the main blocks are made via terminal labeling in the schematic User connections for particular applications can be added as required TEMPERATURE SENSOR A DRIVE Rig ENCODING LOGIC 270 VOUT I1 Tee UA TaHCos 0 T i Ta g R42 3 MOTOR 10k CURRENT LIGHT SENSOR m DRIVERS R31 gt U6B A 7200 VOUT UGH pwm Te EEE fofaf LCDI vimase ne eeu 2 p PMOSFET U3 ENABLES A TaHcoo U4 R40 ia wpe orap FULL 7 EER sspicitLcp Bee L9lolo Pall UB co y ANALOGUE TEST INPUTS 8830 e ue S Ne Eda wh DRIVES 6 Tli 9jeje E 3y p 2 S438 pol pid o2 psp os p61 pz sela abe DADODO g TEAST 36 R35 R34 R33 R26 R33 R37 R39 lt FAULT 270R US LEDS r zaco a vje ACTIVE R47 8 are el al el al el el s 10 3 12 HeH s sl a4 eh ah ah 8 10 Ha Pa vr Sa 1 5 an ay PWM
186. es while 1 place GOTO 0x29 at main loop end if input PIN_A4 Select file bank 1 Set RA4 as input Select file bank 0 Test input RA4 and skip next block if high output C x Select file bank 0 GPRO OxFF GPRO 0 x 00 Select file bank 1 Port C output Select file bank 0 Output x Increment x Load delay value into GPR2 Jump to delay routine Jump back to start of main loop Shut down not normally executed Word 1 3F73 RC NOWDT PUT NODEBUG NOPROTECT BROWNOUT NOLVP NOCPD NOWRT Software Design Using CCS C 219 the compiler does not rely on this The format of the file registers in Bank 0 is shown in Figure B 2 The program then jumps over the delay function block The main block starts by initializing the memory bank selection and the analog inputs The variable x is then declared and the compiler allocates file register 0x21 GPR1 as its storage location The statement while 1 at the start of the main loop instructs the compiler to place a GOTO at the end of the loop with the address of the first loop instruction as its destination address 0x29 The if statement is implemented by first setting the pin RA4 as input then testing it We can see here that the pin initialization is repeated every time the statement is executed This is an example of an operation where C is clearly less efficient than assembler where the pin would normally be initia
187. est Circuit Alternatively the low resolution mode can be used if an 8 bit conversion is sufficiently precise output 0 255 This mode is selected using the directive device ADC 8 The function read_ADc then returns the input value as an unsigned integer The default input voltage range is 0 5 V which does not give an exact conversion factor In the demo program Listing 3 1 the 8 bit input value is divided by 32 to give an arbitrary voltage level from 0 to 8 This is then converted to the ASCII code by adding 0x30 and sending it to the display The operation is repeated endlessly using the statement for which means execute a for loop unconditionally Voltage Measurement The circuit shown in Figure 3 2 allows the input voltage at each analog input to be displayed An external reference voltage 2 56 V is connected to RA3 which sets the maximum of the input range This allows a more accurate and convenient scaling of the measurement The reference voltage is supplied by a zener diode and voltage divider C Peripheral Interfaces 101 Listing 3 1 Source Code for Simple Analog Input Test Program ANALIN C MPB 5 1 07 Read amp display analog input KREKKKRKEKKK KKK KEKE KEE KER EKER ER RR ERE EERE KEKE RKEEKEREREKREKREREREREKER include 16F877A h device ADC 8 8 bit conversion use delay clock 4000000 use rs232 baud 9600 xmit PIN_DO rcv PIN_D1 LCD output void main LEE EKK kk kkk KERR KKK
188. external interrupt define INT_AD 0x8C40 Identify ADC finished interrupt define INT_TBE 0x8C10 Identify RS232 transmit done interrupt define INT_RDA 0x8C20 Identify RS232 receive ready interrupt define INT_TIMER1 0x8C01 Identify Timerl overflow interrupt define INT_TIMER2 0x8C02 Identify Timer2 overflow interrupt define INT_CCP1 0x8C04 Identify Capturel or Comparel interrupt define INT_CCP2 0x8D01 Identify Capture2 or Compare2 interrupt define INT_SSP 0x8C08 Identify Synchronous Serial Port interrupt define INT_PSP 0x8C80 Identify Parallel Slave Port interrupt define INT_BUSCOL 0x8D08 Identify I2C Bus Collision interrupt define INT_EEPROM 0x8D10 Identify EEPROM write completion interrupt define INT_TIMERO 0x0B20 Identify Timer0O overflow interrupt define INT_COMP 0x8D40 Identify Analog Comparator interrupt list device PIC16F877A 86 Part 2 define PIN AO 40 The define directive causes simple text replacement in the source code and is used primarily for defining constants that is fixed values used in the program As can be seen most of the header file consists of this directive In the previous example the compiler replaces the text PIN_AO with the number 401 which specifies bit 0 of file register 5 in the PIC register set 5x8 40 We can therefore deduce that the compiler identifies each bit in the file registers by counting from zero file register 0 bit 0 through all the re
189. ferable in C programs designed for microcontrollers with limited RAM Explain how the use of functions leads to well structured C programs and the benefits of this design approach State the meaning of the source code items that are underlined int out int16 t int16 n while input PIN_DO outbyte for n 1 n lt t n return outbyte 96 Part 2 16 Outline briefly the format of the RS232 signal and how it is used to operate a serial alphanumeric LCD 17 Draw a simple flowchart to represent a function to scan the keys of a numerical keypad and return a code for a key press 18 Explain the meaning of each component of the statement printf d anum n 19 Explain the significance of the amp and operators in C 20 State the function of the compiler directives a include b define c use d device e asm Assignments 2 To undertake these assignments install Microchip MPLAB www microchip com Labcenter ISIS Lite www proteuslite com and CCS C Lite www ccsinfo com Application files may be downloaded from www picmicros org uk Run the applications in MPLAB with Proteus VSM selected as the debug tool Display the animated schematic in VSM viewer with the application COF file attached to the MCU see the appendices for details Assignment 2 1 Download the OUTBYTE DSN file and attach ENDLESS COF Check that it works correctly Modify the program so that the LED out
190. file 215 19 source code 211 12 BARI COF 221 BARI DSN 205 221 BARI LST 215 BASE basic application and system evaluation board 186 9 BCD count program 152 153 Binary coded decimal BCDx digits 152 Blank program 47 48 Block rotate 249 Break continue and goto 57 9 Breakpoint button 223 Brown out Reset BoR 10 Cc C compiler comparison 227 HiTech PIC C 227 230 3 Matrix Multimedia C 227 234 6 Microchip C18 227 228 30 Mikroelektronika C 227 234 235 for PIC 16 series M 237 C interrupts 104 5 C mechatronics applications PICDEM 137 analog sensors 162 6 board simulation 171 5 DC motor test programs 152 6 liquid crystal display 146 52 272 Index C mechatronics applications Continued mechatronics board overview 137 46 stepper motor control 156 62 temperature controller 166 71 C peripheral interfaces PIC16C 99 analog input 99 103 analog output 127 32 EEPROM interface 126 7 128 hardware timers 108 13 PC serial bus 118 21 interrupts 104 8 parallel and serial interfaces 121 5 C program structure 60 2 C programming essentials PIC16 C 35 40 assembler routines 86 94 compiler directives 77 86 data operations 47 55 data types 73 7 functions and structure 60 4 input and output 64 73 program basics 40 7 48 sequence control 56 60 61 C Programming Language The 23 C18 program 230 C18 User Guide 228 229 CALC C 69 70 3 Capture Compare and PWM CCP modules 109 Capture hardware block diagram 112 Cap
191. from assembly code where each instruction has a corresponding mnemonic form that is PIC Microcontroller Systems 23 more easily recognizable such as MOVEF05 W move the data at Port A to the working register This low level language is fine for relatively simple programs but becomes time consuming for more complex programs In addition assembly language is specific to a particular type of processor and therefore not portable Another level of abstraction is needed requiring a high level language C has become the universal language for microcontrollers It allows the MCU memory and peripherals to be controlled directly while simplifying peripheral setup calculations and other program functions All computer languages need an agreed set of programming language rules The definitive C reference is The C Programming Language by Kernighan and Ritchie second edition incorporating ANSI C standards published in 1983 A processor specific compiler converts the standard syntax into the machine code for a particular processor The compiler package may also provide a set of function libraries which implement the most commonly needed operations There is variation between compilers in the library function syntax but the general rules are the same Usually a choice of compilers is available for any given MCU family Options for the PIC at time of writing are Microchip s own C18 compiler Hi Tech PICC and CCS C CCS was selected for the
192. g 5 5 Blank RTOS Program RTOS1 C Minimal blank RTOS program TILITIIITIIIT IIA TIAA TTT TAA TAIT TAIT TITT ITI TTT TTA TAT T include lt 18F452 h gt Define MCU use delay clock 20000000 Define clock rate use rtos timer 0 minor_cycle 100ms Define RTOS timing Task functions 1 0111TITITITTTATAT AAA AAA AAA AAA AA ATT task rate 1000ms max 100ms Define first task void task1 Taskl statements task rate 500ms max 100ms Define another task void task2 Task2 statements J task rate 100ms max 100ms Define last task void task3 Task3 statements Main function 000117 01TTTTITTATA TIAA AT ATTA AAT void main rtos_run Start RTOS scheduler are supplied that allow the tasks to work together for optimum effect For example rtos_enable task1 and rtos_disable task1 allow tasks to be selectively enabled and disabled The function rtos_yield allows the task to return control to the scheduler when finished Some functions allow status information and messages to passed between tasks and the progress of the tasks to be monitored The RTOS is implemented with a total of only 13 functions and directives see the CCS C Compiler Reference Manual A good general explanation of RTOS principles and types can be found in the Salvo RTOS User Manual Chapter 2 from Pumpkin Inc www pumpkininc com PIC16 C Applicatio
193. g hardware RS232 port include 16F877A h use delay clock 8000000 Delay function needed for RS232 use rs232 UART1 Select hardware UART void main ERR kkkkkk kkk kkk kk kkk kkk kk kkk kkk kkk kk int incode setup_uart 9600 Set baud rate while 1 incode getc Read character from UART printf ASCII d incode Display it on pute 13 New line on display 116 Part 3 3 5 PIC16 C SPI Serial Bus e SPI system connections e SPI function set e SPI test system The serial peripheral interface master controller uses hardware slave selection to identify a peripheral device with which it wishes to exchange data refer to Section 1 4 for full details of the signaling protocol The available set of SPI driver functions are shown in Table 3 7 The test system has a slave transmitter that reads a binary coded decimal input from a thumbwheel switch and sends it to the master controller This resends the code to the slave receiver which outputs to a BCD display 0 9 Each of three devices needs its own test program to make the system work The test system hardware is shown in Figure 3 8 and the individual test programs as Listings 3 7 3 8 and 3 9 As seen in the schematic the slave MCUs are permanently enabled by connecting their slave select inputs to ground This is possible because there is only one sender on the master input so there is no potential contention In a system with more th
194. g just over 1 V When this voltage is exceeded the comparator output triggers the overcurrent latch which disables the bridge drivers via their control logic This latch 174 Part 4 needs to be reset via the CLR FAULT push button on power up or when an overcurrent condition has been cleared Logic functions controlling each half bridge driver have been derived from inspection of the control logic in the schematics of the mechatronics board in the PICDEM User Manual Source FET on Pg P F M N Sink FET on Ng M N F where Pg PMOSFET gate active low Ng NMOSFET gate active high N N input from MCU P P input from MCU M PWM input from MCU F FAULT input disable all outputs The operation of each bridge driver deduced from these functions is represented in Table 4 8 which shows only the significant logic conditions The full logic table confirms that the important fact that the FETs are never on at the same time which would effectively short out the drive supply F always disables the output when low power up condition from the overcurrent circuit For most input combinations the half bridge is disabled safe When the bridge control inputs are not connected the P and N inputs are pulled low 0 the M input pulled high 1 logic states shown in bold and the outputs are disabled Pg 1 Ng 0 State 2 They are also unconditionally disabled when F is low Fault mode State 1 Table 4 8 B
195. g programming and debugging for many Microchip Technology Inc MCUs Microchip Technology has always offered a free Integrated Development Environment IDE including an assembler and a simulator It has never been less expensive to get started with embedded microcontrollers than it is today While MPLAB includes the assembler for free assembly code is more cumbersome to write in the first place and also more difficult to maintain Developing code using C frees the programmer from the details of multi byte math and paging and generally improves code readability and maintainability CCS and Hi Tech both offer free student versions of the compiler to get started and even the full versions are relatively inexpensive once the savings in development time has been taken into account xii Foreword While the C language eliminates the need to learn the PIC16 assembly language and frees the user from managing all the details it is still necessary to understand the architecture Clocking options peripherals sets and pin multiplexing issues still need to be solved Martin s book guides readers step by step on the journey from this is a micro controller to here s how to complete an application Exercises use the fully featured PIC16F877A covering the architecture and device configuration This is a good starting point because other PIC 16s are similar in architecture but differ in terms of IO lines memory or peripheral sets
196. g the contents_of operator If a function needs more than one argument the constants may be combined with an OR operator 1 so that the active bits from more than one control code take effect 2 9 PIC16 C Assembler Routines e Reasons for using assembly language e Insertion of assembler sequence e Overview of assembly language C Programming Essentials 87 The default programming language of any microprocessor or microcontroller is its own assembly language The syntax used for any given processor is determined by its internal architecture and the machine code instructions that control it Assembly language is the first level abstraction from machine code where each instruction is represented by a corresponding text mnemonic Program Compilation When compiled a C program is converted into assembler then to machine code We also have seen that one C statement translates into a whole sequence of assembler instructions Since each C statement is independently translated into machine code there is often unnecessary duplication of instructions For example each time a port is accessed the required initialization is repeated As a result the assembler program derived from C source code is always considerably longer than an equivalent assembler program that performs these functions For this reason many compilers contain optimization routines that try to minimize this problem by analyzing the compiler code and eliminating redund
197. gisters In other cases a setup code for loading into a control register is defined as follows define T1 INTERNAL 0x85 In the header file the constant values are associated mainly with the chip hardware e g T O pin identification or constants used in the CCS I O functions However they can also be used to specify alternate function names and to create a MACRO This is a block of replacement code allowing a frequently used code sequence to be replaced with a macro name We use it later to simplify the LCD driver code list nolist These turn the C source code insertion within the assembler list file on and off It is turned off at the beginning of the header file to stop the source code window being filled with the header file then turned on again at the end to show the user source code which follows byte bit These are used to specify the address to be used for a particular bit or byte sized variable Comments have been added to the header file in Listing 2 19 to clarify the function of some directives For more details on the meaning of the defined constants refer to the MCU data sheet and CCS Compiler Reference Manual Generally the constants are values to be loaded into the control registers to set up a specific peripheral interface Not all the options available within the MCU control registers are available as C function options If necessary control bits in the peripheral setup registers can be written directly usin
198. gure 4 8 The first program just switches the motor on and off and the second shows how to control the speed Basic Control The minimal program Listing 4 5 shows how to run the mechatronics board under the control of SW2 The motor is connected to Drivel and Drive2 output terminals with two output bits of the MCU linked to P1 and N2 When these go high the motor current is switched on in a forward direction The output code 0x90 10010000 switches on RD4 and RD7 when the switch input RA4 goes low If desired the PIC output pins can also be monitored on the LEDs The project should be loaded and tested as described in Section 4 1 C Mechatronics Applications 153 Listing 4 4 LCD Counting Program TITTITITTTTI TIT TIAITATTI TTT TIT ITTI A TTT TA TTI TA ITI TA T A TAT A ITI TA I A I TTT LCD2 C MPB 20 4 07 LCD program to count up when SW2 on Hardware Connect SW2 to RA4 11111 1111 111 1 1 11 1 1 1 11 1 1 11 11 1 1 1 1 1 11 1 1 1 11 11 11 1 1 1 1 1 1 1 1 11 11 11 11 111 11111 include 16F917 h include lcd inc Include file with LCD data use delay clock 8000000 void main 1111111111ITITITITITTTTTTST TTT T int8 BCD1 0 BCD2 0 BCD3 0 BCD count digits setup_lcd LCD_MUX14 0 Initialize 14 pin LCD while 1 GENERATE DECIMAL COUNT if input PIN_A4 Test Switch 2 delay_ms 10 Debounce and slow BCD1 Increment ones if BCD1 10
199. he mouse pointer and the effect can be seen on screen in real time The design of the circuit obviously requires knowledge of the relevant interfacing techniques to connect up peripheral components correctly For example the resistor value in the switch pull up circuit is not critical but the maximum value is limited by the input current drawn by the PIC input a maximum of 1 MQ is appropriate At the low end of the viable range power conservation is the relevant factor To limit the current when the switch is closed a resistor value of at least 1 kQ is required 10kQ is a suitable compromise The resistance of each element in the series resistor pack controlling the LED segment currents must be calculated If the LED current required is assumed to be 10 mA and the Hardware Design Using ISIS Schematic Capture 205 Ss bart ISIS Professional Fle View Edt Library Took Desg Gach Source Debug Template System Help OSB n SA Be 4QQQag voaa SERB RPE SEFsa D CUB Se Meru Z Appendct d a aA aa Ae xttascwgaa ae ber MPLAB F Adobe Reade Maes C r2mei007 Figure A 2 ISIS Schematic Capture Screen forward volt drop of the LED is 2 V then the resistor value is given by R 5 2 10 x 107 3002 NPV 270R Refer to Interfacing PIC Microcontrollers Elsevier 2005 by the author for further information on interface design Schematic Edit ISIS is opened as a discrete package within the Proteus VSM suit
200. he ISR task in this case void isrext The interrupt name is preceded by hash to mark the start of the ISR definition and to differentiate it from a standard function block An interrupt name is defined for each interrupt source 108 Part 3 enable interrupts int ext This statement in the main program block enables the named interrupt by loading the necessary codes into the interrupt control registers These are defined in the device header file by association with the interrupt label enable interrupts global This is required in all cases allowing all interrupts to be enabled or disabled together The corresponding global disable function might be used to turn off all interrupts when a timing critical task is to be executed ext int edge H TO L The active edge of the external input can be selected as the falling H_TO_L or rising L_TO_H edge As in this example a manual switched input is usually wired as active low and the falling edge is therefore used On the other hand it may be preferable to use the rising edge since there is no switch bounce when the contacts are opening Further examples of interrupts are provided later among the peripheral interfacing demo programs 3 3 PIC16 C Hardware Timers e Counter timers e Capture and Compare e Timer interrupt The PIC 16F877 has three hardware timers built in TimerO originally called RTCC the real time counter clock Timer1 and Timer2 The principal mo
201. he PIC chip to display the component properties Figure C 1 The folder browse button allows the COF file to be opened attached to the virtual processor and the MCU clock frequency can be set at the same time The 4 MHz is a useful default clock frequency as this gives a 1 1s instruction cycle time and is the maximum frequency using a standard crystal XT mode in the chip configuration settings This clock setting must be passed to the delay routine in the program The Program Configuration Word has no significant effect at this stage but must be set as appropriate when programming real hardware Program Debugging The program can be run by pressing the Play button in the control console If the program is correct the specified output is seen The bar graph displays a binary count when 222 Appendix C i Edit Component Component Reference 1 Component Value PIC16F877 PCB Package DIL40 Progam File barl cof t lage a x Processor Clock Frequency 4MHz Let Le Let Le Progam Configuration Word Ox3F FB Advanced Properties Randomize Program Memory _x No K Other Properties gt Attach hierarchy module Edit af properties as text Figure C 1 MCU Properties Dialog for Attaching the Program the Input button on the schematic is pressed using the mouse pointer It should take 2 56 sec to cycle through all the output codes with a loop delay of 10 ms This can be chec
202. he delays in the RTOS are implemented using the standard function where the MCU clock rate has to be specified 20 MHz The directive use rtos indicates to the compiler that this program uses the RTOS structure It then expects some task definitions to follow and the main block to contain the statement rtos_run The hardware timer used to produce the timer interrupt that triggers task switching is specified as an argument of the directive Timer0 in this case The minor cycle defines the maximum time for which the task runs Each individual task execution rate must be a multiple of this time The task definitions follow Each is preceded by the directive task so that the compiler knows this is an RTOS task and not a standard function definition The rate specifies how often the task executes e g once per second for Task 1 and max is the maximum time allowed for this task The task block is then defined as a sequence of statements in the same way as a standard function but bear in mind that its execution can be suspended and restarted at intervals defined by the RTOS All that remains then is to start up the RTOS in the main block and the tasks are executed in turn with the frequency and duration specified for each The CCS implementation is classified as a cooperative multitasking RTOS This means that the tasks return control to the scheduler voluntarily to allow the next to run A set of functions 194 Part 5 Listin
203. he effect of the following statements on active high LEDs connected to Port D assuming an active low switch circuit is connected to pin RC7 output_D 255 delay_ms 1000 while input PIN_C7 output_D 15 output_D 0 C Programming Essentials 95 10 11 12 13 14 15 Calculate the highest positive number that can be represented by the following variable types a 8 bit unsigned integer b 16 bit signed integer c 32 bit floating point number Estimate the degree of precision provided by the following numerical types as a percentage to two significant figures a 8 bit integer b 32 bit FP number Work out the value of the FP number represented by the binary code 1000 0010 0011 0000 0000 0000 0000 0000 Write a C statement to convert numbers 0 to 9 to their ASCII hex code using variables n for the number and a for the ASCII code and send it to serial LCD State the result of each of these operations in decimal and 4 bit binary if n 5 and m 7 a nt b m c n amp m d n m e nam State the effect of the jump commands continue break and goto label when used within a program loop A menu is required with a choice of three options to be selected by a numerical variable x 1 2 3 Each option is implemented in a separate function funx Write a C code section to show how switch can be used to implement the menu Explain why the use of local variables is pre
204. he fault output high resetting the latch The MOSFET is switched by applying 5 V between the gate and source with the load connected to the drain The NMOSFET has its source connected to 0V and is switched on with 5V at the gate the PMOSFET has its source connected to 5V and is switched on with OV at its gate This provides symmetrical drive components in the half bridge Connect the motor between Drives 1 and 2 Enable drive at P1 from MCU RD7 and control N2 from MCU CCP2 RD2 PWM output is generated from the CCP2 module which controls the speed of the motor Answers 267 20 Output sequence at Port D 0x80 0x10 0x40 0x20 PWM inputs not connected 1 enabled Outputs high RD7 P1 N2 RD4 P4 N3 RD6 P2 N1 RDS P3 N4 Drive sequence Winding forward Drivel Drive2 Winding reverse Drive4 Drive3 Winding1 reverse Drive2 Drive1 Winding forward Drive3 Drive4 Assessment 5 1 Hysteresis means that the switching level of the input depends on the polarity of the input change This helps overcome noise on the input which would cause unreliable switching by implementing an upper and lower switching levels set_adc_channel 0 numin read_adc In the read statement the input value returned by the function has to be assigned to another variable for processing In the channel select statement the channel number is passed fo the function as the function argument See the figure 1
205. he more information is needed in the header Information about the author and program version and or date the compiler version and C Programming Essentials 47 the intended target system are all useful The program description is important as this summarizes the specification for the program Blank Program A blank program is shown in Listing 2 8 which could be used as a general template We should try to be consistent in the header comment information so a standard comment block is suggested Compiler directives are preceded by hash marks and placed before the main block Other initialization statements should precede the start of the main control loop Inclusion of the unconditional loop option while 1 assumes that the system will run continuously until reset We now have enough vocabulary to write simple C programs for the PIC microcontroller A basic set of CCS C language components is shown in Table 2 1 Don t forget the semicolon at the end of each statement 2 3 PIC16 C Data Operations e Variable types e Floating point numbers e Characters e Assignment operators A main function of any computer program is to carry out calculations and other forms of data processing Data structures are made up of different types of numerical and character variables and a range of arithmetical and logical operations are needed Microcontroller programs do not generally need to process large volumes of data but processing speed is often
206. he primary product line of Matrix Multimedia is a user friendly hardware system E blocks that allows different systems to be assembled using plug in modules The www newnespress com C Compiler Comparison 235 Listing D 4 MikroC Source Code Sample ADC Input and Display unsigned inval 16 bit integer for 10 bit input void main ADCON1 0x80 Setup ADC TRISA OXFF Analog inputs TRISB 0x3F RB6 RB7 display outputs TRISD 0 Port D display outputs do inval Read_ADC 2 Read channel 2 RA2 PORTD inval Show low 8 bits PORTB inval gt gt 2 Show high 2 bits while 1 Figure D 2 Matrix Multimedia Modular PIC System processor module incorporates sockets for a range of PIC MCUs and a number of D type connectors Peripheral modules with push buttons LEDs displays keypad relays communications interfaces and so on are added as required Figure D 2 www newnespress com 236 Appendix D Listing D 5 Matrix C Source Code Sample ADC Input and Display include lt system h gt void setupADC void trisb 0x00 Port B display trisa 0xf1 RAO input RA1 3 output EN adcon0 0x00 Set up ADC y adcon1 0x80 Set up ADC Xf ansel 0x01 Select AN0 only xy void main void setupADC Call setup function while 1 Loop always adcon0O 0x05 Start ADC while adcon0 amp 0x04 Wait until
207. hen the higher priority ISR is being executed the lower priority interrupt can be disabled or masked until it is finished In more complex programs numerical levels of priority can be assigned with higher priorities taking precedence Unfortunately the 16 series PIC is not well suited to this as it does not have a built in priority system unlike more powerful processors Further the different interrupt sources have to be identified explicitly by a user routine An operating system OS provides an alternative to interrupts as a means of providing a more predictable time response in the microcontroller system but again is typically implemented in the higher power MCU type such as the PIC18 or 24 series Nevertheless to point the way ahead the principles are outlined here PC Operating System The most well known example of an operating system is Microsoft Windows Why is this needed in PC type computers The answer is simply the complexity of the software 192 Part 5 compared with a microcontroller The operating system provides a collection of the numerous program components required to run the computer Each peripheral interface has its own driver keyboard screen disks mouse network etc plus modules for memory management and general system control Therefore the PC needs a more sophisticated task management system A lengthy process such as printing or disk access cannot be allowed exclusive use of the system resource
208. her a comparator or an ADC input The drive control logic is also modeled using generic devices for the discrete CMOS gates but with specific devices for the enable logic The driver MOSFETs themselves are generic so actual device characteristics may not be represented exactly This is not a significant issue since the motor models are also generic The PMOSFET is switched on when its gate is taken low and the NMOSFET is switched on when its gate is logic high No additional interfacing is necessary which is a great advantage of the FET over other types of current driver such as bipolar power transistors In addition the FET is voltage operated and input resistance at the gate is very high giving negligible loading on the control logic outputs The flywheel diodes in the output are added to cut off the back emf from the inductive motor load when switching off the windings a standard arrangement with inductive loads This high voltage pulse could otherwise damage the FETs The specific FETs used in the actual hardware have Schottky diodes across the outputs which perform a similar protection function A motor overcurrent is detected by a 0 1 resistor through which all driver currents flow to the ground This generates a voltage of 100 mV at 1 A and a noninverting amplifier with a gain of 10 increases this to 1 0 V This voltage is monitored by a comparator stage which has a reference voltage generated by a pair of diodes in series givin
209. hile count gt 99 Calculate hundreds count count 100 huns _ digit by subtraction while count gt 9 Calculate tens count count 10 tens digit by subtraction ones count DISPLAY BCD DIGITS 1 111111 11111111 17 1lcd_symbol DigMap ones DIG1 Display Digit 1 1lcd_symbol DigMap tens DIG2 Display Digit 2 1lcd_symbol DigMap huns DIG3 Display Digit 3 Loop always J ND 156 Part 4 Listing 4 7 Outline of Rev Counter Program MOTREVS Specify MCU 16F917 Include LCD function file Initialize display digits to zero Setup LCD Setup timer as external pulse counter Main loop Display 3 digits on LCD Wait for input switch on Reset counter and start motor Wait for input switch off Stop motor Convert timer count to 3 digit BCD The timer is set up for external input using setup_timer_1 T1_EXTERNAL and the resulting count is read using get_timer1 The binary number obtained from the timer is divided by 2 and converted to BCD by a process of successive subtraction which is simple if not elegant The calculated digits are then displayed as in previous examples using the function 1cd_symbol1 to output the display digits and the include file LCD INC for the display encoding 4 4 PICDEM Stepper Motor Control e Stepper motor operation e Stepper motor test program e Speed and direction control The main advantag
210. ides the features required for this application at minimum cost Hardware Design Using ISIS Schematic Capture Proteus VSM is an interactive electronics design package from Labcenter Electronics that allows analog digital and microprocessor circuits to be subjected to virtual testing before the creation of a PCB layout for the construction of real hardware ISIS is the schematic capture package and ARES is the layout package The circuit is entered directly onto the schematic by selecting components from a library of parts which have associated mathematical models e g V IR for a resistor When completed the wiring schematic is converted to a set of nodes connected by components represented by a set of simultaneous equations derived from the model for each component The network is solved for any given set of inputs and the outputs are displayed via active on screen components virtual instruments or charts The microcontroller is simulated on the basis of its internal architecture and the specific program being executed which must be attached to complete the model In our case the program is written in C and the COF file produced by the compiler attached to the MCU This file contains the program machine code and some additional information to help with debugging the program ISIS allows the source code and variables to be displayed so that the program operation can be studied step by step and any functional errors corrected Desig
211. ific pins The hardware features of all these are outlined so that I O programming can be more readily understood later on The application development process is described using only MPLAB IDE in this initial phase A sample C program is edited compiled downloaded and tested to demonstrate the basic process and the generated file set analyzed The debugging features of MPLAB are also outlined run single step breakpoints watch windows and so on Disassembly of the object code allows the intermediate assembly language version of the C source program to be analyzed Part 2 introduces C programming using the simplest possible programs Input and output are dealt with immediately since this is the key feature of embedded programs Variables conditional blocks IF looping WHILE FOR are quickly introduced with a complete example program Variables and sequence control are considered in a little more detail and functions introduced This leads on to library functions for operating timers and ports The keypad and alphanumeric LCD are used in a simple calculator program More data types long integers floating point numbers arrays etc follow as well as assembler directives and the purpose of the header file Finally insertion of assembler into C programs is outlined xviii Introduction Part 3 focuses on programming input and output operations using the CCS C library functions These simplify the programming process with a small
212. igure 4 10 in the actual motor coils are distributed around the whole circumference multiplying the torque produced Their terminals are 158 Part 4 connected to the four driver outputs on the board which are normally connected for full bridge operation This allows the current to be reversed in the stator windings reversing the polarity of the stator poles The stator coils are brought out to four color coded wires which are connected to the driver terminals In more expensive motors a smaller step typically 1 8 can be obtained with four sets of windings These motors usually have six wires with a common connection for each pair of windings Stepper Motor Test The stepper motor is connected to the driver outputs in clockwise order The six driver input links must be closed to enable full bridge operation since the bipolar motor requires winding current in both directions P1 P2 P3 and P4 inputs are connected to RD4 RD5 RD6 and RD7 respectively When run the program generates the required switching sequence on the coils to energize them in the right order SW2 RA1 changes the direction and SW3 RA3 and SW4 RA4 allow the step speed to be varied Source code STEPTEST C is shown in Listing 4 8 Only the control inputs P1 P2 P3 and P4 need to be connected to outputs RD7 RD4 at this stage Note that the stepper motor terminal connections are not in numerical color order As can be seen no special program setup is needed
213. imes include 16F877A h use delay clock 1000000 void main int x while input PIN_CO Wait until switch closed for x 0 x lt 5 X For loop conditions output_high PIN_DO Flash sequence delay_ms 500 output_low PIN_DO delay_ms 500 while 1 Wait for reset FOR Loop The WHILE loop repeats until some external event or internally modified value satisfies the test condition In other cases we need a loop to repeat a fixed number of times The FOR loop uses a loop control variable which is set to an initial value and modified for each iteration while a defined condition is true In the demo program FORLOOPC Listing 2 6 the loop control parameters are given within the parentheses that follow the for keyword The loop control variable x is initially set to 0 and the loop continues while it is less than 6 Value x is incremented each time round the loop The effect is to flash the output five times The FORLOOP program also includes the use of the while loop to wait for the switch to close before the flash sequence begins In addition an unconditional while loop terminates the program preventing the program execution from running into undefined locations after the end of the sequence This is advisable whenever the program does not run in a continuous loop Note that the use of the empty braces which contain no code is optional SIREN Program A program combining some of the
214. important Variable Types Variables are needed to store the data values used in the program Variable labels are attached to specific locations when they are declared at the beginning of the program so the MCU can locate the data required by each operation in the file registers 48 Part 2 Listing 2 8 Program Blank Source Code Filename ia Author Date Version Program Description Hardware simulation TITTITTTTTTITTTTT TTA TTT ATTA TTA TAA TATA TT AAA ATTA TTT include 16F877A h Specify PIC MCU use Include library routines void main Start main block int Declare global variables while 1 Start control loop Program statements End main block Table 2 1 A Basic Set of CCS C Source Code Components C Compiler Directives include source files use functions parameters Include source code or header file Include library functions C Program Block main condition statements while condition statements if condition statements for condition statements Main program block Conditional loop Conditional sequence Preset loop CCS C Library Functions delay_ms nnn delay_us nnn output_x n output_high PIN_nn output_low PIN_nn input PIN_nn Delay in milliseconds Delay in microseconds Output 8 bit code at Port X Set output bit high Set output bit low Get input C Programming Essentials 49 Table 2 2
215. inally specify the power supply Obviously power consumption is even more critical in battery powered systems Software Design There are two main options for creating the system firmware for low complexity embedded systems assembly language or C There are other user friendly programming options aimed primarily at learners such as software that allows C code to be generated from a flowchart see Appendix D A wider range of high level languages and proprietary development systems are available to support more advanced processors In general assembly language is used for simple programs and those where direct access to control registers or speed is critical Certainly using assembler requires an intimate knowledge of the MCU architecture and is an essential tool for the practicing embedded engineer If necessary assembly language blocks of code can be embedded within a C program However the premise of this book is that there are good arguments for starting with C Less detailed hardware knowledge is needed and programming is simplified It is also a universal language whereas each MCU type has its own assembly language Used in conjunction with a user friendly simulator such as Proteus useful applications for any microcontroller type can be created with a minimum of experience The availability of a comprehensive set of peripheral drivers is also very helpful as provided by CCS C However the main advantage is that C is by far the mos
216. ing character codes via a serial line was originally used in mainframe computer terminals to send keystrokes to the computer and return the output that is how long it s been around In this example the LCD receives character codes for a 2 row X 16 character display The program uses library routines to generate the RS232 output which are called up by the directive use RS232 The baud rate must be specified and the send TX and receive RX pins specified as arguments of this directive The directive must be preceded by a use delay which specifies the clock rate in the target system The LCD has its own controller which is compatible with the Hitachi 44780 MCU the standard for this interface When the system is started the LCD takes some time to initialize itself its own MCU needs time to get ready to receive data A delay of about 500 ms should be allowed in the main controller before attempting to access the LCD A basic program for driving the LCD is shown in Listing 2 15 Characters are sent using the function call putc code whose argument is the ASCII code for the character the ASCII table given previously Table 2 5 lists the available codes Note that the codes for 0 to 9 are 0x30 to 0x39 so conversion between the code and the corresponding number is simple Characters for display can be defined as A to Z and so on in single quotes in the program The character is then replaced by its code by the compi
217. inimum time required to transmit this page over a 9600 baud RS232 link and an SPI line under the control of an MCU running at 20 MHz stating any assumptions made 17 State the function of each of the C project files that have the following extension C HEX COF LST and ERR 18 State the function of the five connections in the PIC in circuit programming and debugging interface 19 Study the content of the dissembler window in Figure 1 22 and state the function of the five visible windows 20 List a minimum set of development system hardware and software components required to create a C application for the PIC microcontroller Assignments 1 Assignment 1 1 Download the data book for the PIC16F87X MCUs from www microchip com Study Figure 1 2 the PIC16F877 block diagram Describe in detail the sequence of events that occurs when the data code for 255 9 11111111 from a machine code instruction is output to Port D Refer to the role of the program memory program counter instruction register instruction decoder file register addressing internal data bus and clock What path must the data follow to get from the program memory to Port C Describe the setup required in Port C to enable the data byte to be observed on the port pins Figure 1 4 Refer if necessary to PIC Microcontrollers An Introduction to Microelectronics by the author Assignment 1 2 Research a list of SPI and I C peripherals that might be useful in constr
218. int at the top of the program Run seems to have little effect but if View Special Function Registers is selected Port D can be seen to have been written with the data FF To see the program listed in assembler select View Disassembler Listing This shows an assembler version of the program derived from the compiler output PIC Microcontroller Systems 25 Project Files Let us now look at some of files created in the project folder Some which are concerned with MPLAB project management do not need to be considered at this stage outbyte c The source code file is created in a text edit window in line with the compiler and ANSI C syntax rules For viewing outside MPLAB it can be opened with right click Notepad The syntax requirements are detailed in the C programming sections later outbyte hex The hex file the program download file is shown in Listing 1 2 as it is displayed in a text editor The fact that it is readable shows that it is stored as ASCII characters It must be converted by the program downloading utility to actual binary code for loading into program flash memory in the MCU If the hex listing is compared with the machine code column in the Disassembler listing visible in Figure 1 16 we can see that the first 4 bytes eight digits contain the start address 0000 The program code starts at the ninth digit but the bytes of the four digit instruction code are reversed Therefore the first instruction is code 30
219. ion of the simulation software may be downloaded from www proteuslite com A special offer for ISIS Lite ProSPICE Lite and the 16F877A simulator model can be found at www proteuslite com register ipmbundle htm Proteus VSM ISIS and ARES are trademarks of Labcenter Electronics Ltd Custom Computer Services Inc www ccsinfo com Custom Computer Services Inc specializes in compilers for PIC microcontrollers The main range comprises PCB compiler for 12 bit PICs PCM for 16 bit and PCH for the 18 series chips The support provided by James Merriman at CCS Inc is gratefully acknowledged The manual for the CCS compiler should be downloaded from the company Web site Version 4 was used for this book A 30 day trial version which will compile code for the 16F877A is available at the time of writing xvi Preface The Author s Web Site www picmicros org uk This book is supported by a dedicated Web site www picmicros org uk All the application examples in the book may be downloaded free of charge and tested using an evaluation version of Proteus VSM The design files are locked so that the hardware configuration cannot be changed without purchasing a suitable VSM license Similarly the attached program cannot be modified and recompiled without a suitable compiler license available from the CCS Web site Special manufacturer s offers are available via links at my site This site is hosted by www larrytech com and special thanks a
220. ions Replace label in source code with value Identify MCU type Turn on source code listing Start end of assembler block Select MCU configuration fuse settings Declare function as interrupt service routine Main program block Conditional loop Conditional loop Conditional sequence Preset loop conditions Multichoice selection Star slash enclose block comment Double slash before line comment Braces enclose program block Semicolon end of statement Function arguments parameters comma separates Array size variable ASCII function argument include filename ASCII value 240 Appendix E Basic I O Functions output_X n output_high PIN_Xn output_low PIN_Xn Output 8 bit code at Port X Set output bit high Set output bit low input PIN_Xn Get bit input n input_X Get byte input Variable Types Identifier Type Min Max Range intl 1 bit 0 1 1 2 unsigned ints 8 bits 0 255 256 28 signed int8 8 bits 127 127 255 28 1 unsigned int16 16 bits 0 65 535 65 536 2 6 signed int16 16 bits 32 767 32 767 65 535 2 6 1 unsigned int32 32 bits 0 4 294 967 295 4 294 967 296 23 signed int32 32 bits 2 147 483 647 2 147 483 647 4 294 967 295 2 1 float 32 bits 10 10138 1077 Relational Operators Operation Symbol Example Equal to if a 0 b b 5 Not equal to l if a 1 b b 4 Greater than gt if a gt 2 b b
221. irst argument of the function is an array variable that contains the seven segment code for the number 8 and the second identifies the seven display memory bits for the segments of the digit The DC motor needs position feedback to achieve a set position or speed A slotted wheel and optical sensor produce pulses as the shaft turns allowing the MCU to count the revs completed in unit time The stepper motor has multiple coils which are energized in sequence to turn the shaft so it can be turned through a set number of steps with no feedback required The stepper motor on the mechatronics board has two sets of windings two wires each which are connected to the four drive outputs Connect the motor sensor to Timer1 input and configure the timer to measure the pulse period The Capture mode of operation allows the timer count to be captured when the sensor input changes The MCU program can convert the pulse period into revs sec 1 step 7 5 1 rev 360 7 5 48 steps Time per step 1 48 20 8ms 21 ms The temperature sensor gives an output of 10mV C with an offset of 5 00mV so the temperature can be calculated at any value in that range The light sensor output cannot be quantified in the same way because it is not linear and the absolute level is therefore more difficult to calculate V sensitivity X temp offset 10 xX 25 500 750mV ADC output scaling 2048 1024 2mV bit ADC output value V scaling 750 2
222. is is adequate for most purposes The disadvantage of this format is there are always slight rounding errors so if an integer is converted to a FP number and back it no longer is exact This is illustrated in Figure 2 5 where integer variables have been assigned their maximum values in a demo program and are displayed in the watch window after running in MPSIM The integers are correct but the discrepancy due to rounding errors between the working value of the floating point number and the original can be seen to be 12 3456793 12 3456789 0 0000004 One advantage of C is that the exact method of calculation is normally concealed within the built in functions and operations However we still need to use the most appropriate numerical format because the C compiler does not tell us if the right answer is obtained from any given calculation This is where simulation is useful in real time applications we can check that the answers are correct before they are used to modify control outputs in real hardware The integer types and ranges available in CCS C are shown in Table 2 1 52 Part 2 VARS C Demo of variable types errererorrrcrrrrcorrrrerrrrrr TT Ty include 16F877A h void main m Output Bult Venion Cornel Fire intl ints int16 int32 float char h ibit 1 hibyte 255 hiword 65535 hilong 2147483647 afloate12 3456789 aletter gt gt gt Warming 202 C PIC B gt gt gt Waning 202 C
223. ission T c POLL Check to see if byte received sbit Returns 1 if byte i2c_poll waiting 248 Appendix F Table F 7 Parallel Slave Port Function Description Example Comment PSP ENABLE Enable or disable PSP setup_psp PSP_DISABLED to PSP_ENABLED switch of SET SET DIRECTION Set the PSP data direction set_tris_e 0 Forinputarg OxFF or mixed mode OUTPUT READY Checks if output byte is pspo psp_ Byte ready pspo 1 ready to go output_full To write the PSP PSP_DATA outbyte INPUT READY Checks if input byte is pspi psp_ Byte ready pspi 1 ready to read input_full To read the PSP inbyte PSP_DATA PSP OVERFLOW Checks for data overwrite pspv psp_ Check to prevent loss error overflow of data due to external mistiming Table F 8 LCD Control Requires Chip Header File Only e g 16F877A H Function Description Example Comment LCD SETUP Set up LCD internal setup_lcd Number of control control LCD_MUX12 1 lines clock prescale LCD LOAD Send display data lcd_load Pointer offset number block to LCD lcddata 0 16 of bytes LCD SYMBOL Send segment bits lcd_symbol Specify segments lcddata dig1 individually Table F 9 Register Manipulation Function Description Example Comment REGISTER BIT Set a selected bit b
224. it_set num 1 Sets bit b in integer SET num 8 16 or 32 bits REGISTER BIT Clear a selected bit bit_clear num 2 Clears bit b in integer CLEAR num 8 16 or 32 bits REGISTER BIT Test a selected bit flag Tests bit b in integer TEST bit_test num 4 num 8 16 or 32 bits REGISTER SWAP Swap nibbles ina swap abyte Result not returned by byte variable function CCS C Program Function Reference Table F 10 Block Rotate 249 Function Description Example Comment BLOCK ROTATE LEFT Rotates bits of rotate_left Address of low byte LEFT BLOCK SHIFT RIGHT bit of structure bit of structure Shift bit right into high structure left amp lobyte 6 and number of bytes BLOCK ROTATE Rotates bits of rotate_right Address of low byte RIGHT structure right amp lobyte 10 and number of bytes BLOCK SHIFT Shift bit left intolow shift_left Address of low byte amp lobyte 4 1 shift_left amp lobyte 4 1 number of bytes bit in Address of low byte number of bytes bit in Table F 11 Math Functions INCLUDE MATH H Function Description Example Comment ABSOLUTE Absolute value of abres abs x Returns unsigned VALUE integer positive value of signed integer LONG Absolute value of longres labs x Returns unsigned ABSOLUTE long integer positive value of 16 bit integer FLOAT Absolute value
225. its are then clocked in or out of the slave SPI shift register to or from the master Figure 1 13 No start and stop bits are necessary and it is much faster than RS232 The clock signal runs at the same speed as the master instruction clock that is 5 MHz when the chip is running at the maximum 20 MHz 16 series MCUs I7C Bus The interintegrated circuit I7C bus is designed for short range communication between chips in the same system using a software addressing system It requires only two signal wires and operates like a simplified local area network The basic form of the hardware and data signal are illustrated in Figures 1 14 and 1 15 The IC slave chips are attached to a two wire bus which is pulled up to logic 1 when idle Passive slave devices have their register or location addresses determined by a combination of external input address code pins and fixed internal decoding If several memory devices are connected to the bus they can be mapped into a continuous address space The master sends data in 8 bit blocks with a synchronous clock pulse alongside each bit As for SPI the clock is derived from the instruction clock up to 5 MHz at the maximum clock rate of 20 MHz To send a data byte the master first sends a control code to set up the transfer then the 8 bit or 10 bit address code and finally the data Each byte has a start and acknowledge bit and each byte must be acknowledged before the next is sent to improve reliabi
226. kB 75 X 16 bits 16 J series 3V supply C program Power range 3V supply 24FXXXX 100 16 128kB 76 X 24 bits 16 no EEPROM data RAM lt 8 kB C program available in the low pin count LPC ranges 10 12 series while the power ranges are expanding rapidly In addition are those listed in the 24HXXXX range which runs at 40 MIPS and the dsPIC digital signal processor high specification range 1 2 PIC16 MCU Configuration e Clock oscillator types e Watchdog power up brown out timers e Low voltage programming e Code protection e In circuit debug mode When programming the PIC microcontroller certain operational modes must be set prior to the main program download These are controlled by individual bits in a special PIC Microcontroller Systems 9 configuration register separated from the main memory block The main options are as follows Clock Options The 877 chip has two main clock modes CR and XT The CR mode needs a simple capacitor and resistor circuit attached to CLKIN whose time constant C X R determines the clock period R should be between 3k and 100k and C greater than 20 pF For example if R 10kQ and C 10nK the clock period will be around 2 X C X R 200 ps calculated from the CR rise fall time and the frequency about 5 kHz This option is acceptable when the program timing is not critical The XT mode is the one most commonly used since the extra component cos
227. ked using the simulation clock at the bottom of the screen If the program does not work as required it needs debugging The screenshot in Figure C 2 shows some of the debugging features The principal technique is single stepping the program sequence is checked by executing one statement at a time This requires the source code to be displayed pause the program and select the Debug menu PIC CPU Source Code The source code window appears with the current execution point highlighted If the Pause control is pressed instead of Run the program can be single stepped from the first statement This is useful if the initialization sequence needs to be checked It is not possible to operate the debugging tools and the interactive push button with the mouse at the same time Therefore in Figure C 2 the Input button is shorted out with a temporary link so that the output runs continuously Alternatively it can be replaced with a switch for simulation purposes The source code window has a selection of debug buttons Run Step Over Step Into Step Out Of the current function Step Over means execute the following function call at full speed stopping on return while Step Into means execute the function stepwise While stepping through a function Step Out Of allows you to return to the calling block at full speed This is useful for getting out of a function you have inadvertently stepped into System Testing Using Proteus VSM 223 SS bart
228. kipped A default block is executed if none of the options is taken The same effect can be achieved using if else but switch case provides a more elegant solution for implementing multichoice operations such as menus If the case options comprise more than one statement they are best implemented using a function block call as explained in the next section a Condition True Condition True Figure 2 9 Comparison of a If and b If Else 60 Part 2 Test Variable Value lt Value 1 Procedure 1 Value 2 Procedure 2 gt lt Value n Procedure n 4 Default Procedure 4 v Figure 2 10 Switch Case Branching Structure 2 5 PIC16 C Functions and Structure e Program structure e Functions arguments e Global and local variables The structure of a C program is created using functions Figure 2 11 This is a block of code written and executed as a self contained process receiving the required parameters data to be processed from the calling function and returning results to it Main is the primary function in all C programs within which the rest of the program is constructed When running on a PC main is called by the operating system and control is returned to the OS when the C program is terminated In the microcontroller main is simply used to indicate the start of the main control sequence and more care needs to be taken in termi
229. kkkxkxkxkkkkxkxkkkkkxkxkxkkkkxkkkkkkkkkkxkxk void scankey Read keypad void makenum Construct input decimal from keys MAIN PROGRAM Get numbers amp Calculate EAER Ek HiAk KE AAA AEE k ER R k void main for 7I Get MuUMbELr Se oh cee a ea i td is E A RR OR ES OREN delay_ms 500 putc 254 putc 1 delay_ms 10 Clear display numofdigs onesdig tensdig hunsdig 0 akey 0x30 do scankey Get first number putc akey if akey gt 0x30 amp amp akey lt 0x39 makenum while akey gt 0x30 amp amp akey lt 0x39 num1 onesdig tensdig 10 hunsdig 100 Calculate it opcode akey numofdigs onesdig tensdig hunsdig 0 akey 0x30 Get second number do scankey putc akey if akey gt 0x30 amp amp akey lt 0x39 makenum while akey lt 0x30 amp amp akey lt 0x39 num2 onesdig tensdig 10 hunsdig 100 Calculate it Calculate results 203440 24 oki ent ees ae ta eR ae if opcode 0x2F result numl1 num2 if opcode 0x2A result num1 num2 if opcode 0x2D result numl1 num2 if opcode 0x2B result numl num2 f Calc result VdigGtisSs ii oe ed hes Se SE EA ee ie ee aes Se hunthous result 100000 reml result hunthous 100000 tenthous rem1 10000 rem2 rem1 tenthous 10000 thous rem2 1000 rem3 rem2 thous 1000 hunds rem3 100 rem4 rem3 hunds 100 tens rem4 10 ones rem4 tens 10 I Display digi
230. l array to display alphanumeric characters Most LCDs may also be set up to display simple bit mapped graphics In simulation mode an RS232 virtual terminal provides a convenient way of generating alphanumeric input into the MCU for testing The ASCII codes are listed in Table 2 5 Master Serial Data Out SDO Serial Data In SDI Serial Clock SCK Slave 1 Slave 2 SDO SDO SDI SDI gt sck gt sck gt ISS gt ISS Slave Select SS1 Outputs SS2 SS3 gt Figure 1 12 SPI Connections soosi XX 7X 6X5 X 4X3 X21 X O X DataBits SCK Clock Figure 1 13 SPI Signals PIC Microcontroller Systems 21 SPI Bus The serial peripheral interface SPI bus provides high speed synchronous data exchange over relatively short distances typically within a set of connected boards using a master slave system with hardware slave selection Figure 1 12 One processor must act as a master generating the clock Others act as slaves using the master clock for timing the data send and receive The slaves can be other microcontrollers or peripherals with an SPI interface The SPI signals are e Serial Clock SCK e Serial Data In SDD e Serial Data Out SDO e Slave Select SS To transfer data the master selects a slave device to talk to by taking its SS line low Eight data b
231. l more convenient for displaying a fixed string Table 2 10 shows the contents of the RAM file registers after the program ARRAYS has executed It can be seen that the numerical array data has been allocated to locations 0x21 to 0x2A inclusive in the GPRs with the character data in locations 0x2D to 0x32 inclusive The characters are displayed in the right column converted from ASCII The single integers are seen in the locations 0x2B and 0x2C final value Ox0A The data bytes can be accessed directly in these locations using indirect addressing operators Indirect Addressing Operators C provides various ways of manipulating data in memory Since there always seems to be several ways to get the same result this can be confusing for the beginner If a variable Table 2 10 MPLAB Display of Array Data in File Register Address 00 01 02 03 04 05 06 07 08 09 OA OB OC OD OE OF ASCII 000 00 38 1C 00 00 00 00 01 00 00 00 00 00 00 00 Pie Oars de ase EN ett 010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 Le ee eee 020 00 00 01 02 03 04 05 06 07 08 09 OA OA 48 65 6C_ Lee Hel 030 6C 6F 21 00 00 00 00 00 00 00 00 00 00 32 00 18 MOVs sy ecensy koss Des 040 20 20 20 39 14 OA 00 00 00 00 00 00 00 00 00 00 ie EEA AEE AEEA 76 Part 2 5 points MPLAB DE v7 50 Pie Ct View Project Cebugger Programmer Tocs Configure Window Heb Oe mM CAMS Ree SRO 24 cuehePrere CL Wpoints e 5 a POINTS C inc
232. ler The display also needs control codes for example to clear the display and reset the cursor to the start position after characters have been printed These are quoted as an integer decimal and sent as binary Each control code must be preceded by the code 254 1111 1110 to distinguish it from data The code to start the second line of the display is 192 The display reverts automatically to data mode after any control code A basic set of control codes is identified in Table 2 8 In the example program LCD C the sample character acap is upper case A ASCII code 1000001 65 If a string of fixed characters are to be displayed the form printf sample text can be used The meaning of the function name is print formatted We often need to insert a variable value within fixed text in this case a format code is placed within the display text and the compiler replaces it with the value of the variable which is quoted at the end of the printf statement The code d means display the variable value as an integer decimal number c means display the ASCII character corresponding to the number Multiple values can be inserted in order as seen in program LCD C A summary of formatting codes is shown in Table 2 9 C Programming Essentials 67 Listing 2 15 Serial LCD Operation LCD C Serial LCD test send character using putc and printf TIITITITTATI TIAA TTA TAA TTA I TAA TTA AIT AAAI TAT AAAI TTL inclu
233. lity 22 Part 1 5V Master Slave 1 Slave 2 etc gt SDA CH gt SCL Figure 1 14 I C Connections Start Acknowledge Address Data Bits gt SDA DODODODOA X SCL Figure 1 15 I C Signals The sequence to read a single byte requires a total of 5 bytes to complete the process 3 to set the address and 2 to return the data Thus a substantial software overhead is involved To alleviate this problem data can be transferred in continuous blocks memory page read write which speeds up the transmission 1 5 PIC16 MPLAB Projects e MPLAB C Project e Project Files The PIC microcontroller program comprises a list of machine code instructions decoded and executed in sequence resulting in data movement between registers and arithmetic and logic operations MCU reset starts execution at address zero and the instructions are executed in address order until a program branch is decoded at which point a new target address is derived from the instruction A decision is made to take the branch or continue in sequence based on the result of a bit condition test This process is described in detail in PIC Microcontrollers by the author The program could be written in raw binary code but this would require manual interpretation of the instruction set Therefore the machine code is generated
234. lized once only The same problem occurs in the next block when the value of x is output the initialization is repeated each time the statement is executed The delay period 10 is stored in the next available location 0x22 when the delay is called The program then jumps back to the delay code block starting address 0x04 A counting sequence follows which gives a delay of 1 ms This is repeated ten times and the program jumps back to the main block and the main loop repeats Note that assembler instructions CALL and RETURN are not used because this would limit the number of nested routines to eight the limit of the PIC stack depth By using GOTO instead this limitation is avoided by the CCS complier System Testing Using Proteus VSM A hardware design schematic BAR1 DSN has been devised Appendix A and an application program BAR1 C developed Appendix B from the specification These can now be brought together for testing in simulation mode Attaching the Program The application program is output by the C compiler as a file called BAR1 COF which should be stored in the project directory BAR1 It contains the machine code plus some debugging information required by the simulator to display the program source code Several other files are created by the compiler at the same time and all these should be stored in the same project folder containing the ISIS design file BARI DSN On the schematic right click then left click on t
235. llustrated in Figure 1 6 Comparator The comparator Figure 1 7 is an alternative type of analog input found in some microcontrollers such as the 16F917 used in the mechatronics board described later 16 Part 1 Ve Comparator Status Bit Ve gt Vc Ve Figure 1 7 Comparator Operation Chip Select Interrupt Read Write Parallel Slave EXTERNAL Port INTERNAL Data x 8 Data x 8 Figure 1 8 Parallel Slave Port Operation It compares the voltage at a pair of inputs and a status bit is set if the C pin is higher than C The comparator status bit may also be monitored at an output pin The 917 has two such comparator modules they are enabled using a system function to set the operating mode The 877 has no comparators so the ADC must be used instead Parallel Slave Port The parallel slave port on the 877 chip is designed to allow parallel communications with an external 8 bit system data bus or peripheral Figure 1 8 Port D provides the eight I O data pins and Port E three control lines Read Write and Chip Select If data are to be input to the port the pin data direction is set accordingly and data presented to Port D The chip select input must be set low and the data latched into the port data register by taking the write line low Conversely data can be read from the port using the read line Either operation can initiate an interrupt Interrupts Interrupts can be generated by various inte
236. lude 16F877A h main int8 numl 123 point num2 pointi numi um2 y gram Fles CCS PIC Complen PIOC pointa CIFIC BOOKSIPIC Programming b CIFIC BOOKSIPIC Programming b j while 1 ROM 0 RAM rang Loaded CFIC BOOKSIPIC Progr book DUILO SUCCEEDED The Mar 22 20 34 00 2007 lt efx Address 00 01 02 03 04 05 06 07 08 09 0A 08 0C 0D 08 0 SSS 010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 O yabo nans 020 00 7B 21 7B 00 00 00 00 00 00 00 00 00 00 00 00 030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 lt gt Aad Smed COUT Value pointi 0x21 num 0x7B nual Ox7B Watch 1 wistch 2 Watch 3 Watch amp Figure 2 13 Program POINTS C Demonstrating Address_of and Contents_of Operators is declared in C the next available RAM location or locations is reserved for it by the compiler As we have seen CCS C can assign 1 bit 1 byte integer or character 2 bytes integer or 4 bytes integer or float If we initially concentrate on byte storage we can see that it consists of two associated values the address of the location and the contents of the location When a variable is declared its label is assigned to the file RAM address by the compiler When the variable is used this address is used to access the variable value Often it is useful to be able to do this explicitly and some functions require it Therefore the operators address_of amp ampersand and conten
237. mbers 0 5 valid as fitted TIMER CCP SETUP Select PWM Capture or Compare mode setup_ccpl ccp_pwm See CCS manual for CCP options TIMER PWM DUTY Set PWM duty cycle set_pwml_duty 512 512 mark count 50 246 Appendix F Table F 4 RS232 Serial Port Requires USE RS232 USE DELAYS Clock nnnnnnnn Function Description Example Comment SET BAUD RATE Set hardware RS232 port baud rate setup_uart 19200 Applies to hardware serial port only serial port SEND BYTE Write a character to the putc 65 Writes ASCII data or default port control code to serial output SEND SELECT Write a character to s fputc A 01 As preceding but selected port stream identifier given PRINT SERIAL Write a mixed message printf Answer Write fixed strings and 4 3d n formatted variable values PRINT SELECT Write string to selected fprintf As preceding but 01 Message stream identifier given error message PRINT STRING Print a string and write sprintf Print and copy output it to array astr Ans d n to character array RECEIVE BYTE Read a character toan n getc Waits for ASCII code integer from serial input RECEIVE Read an input string to gets spoint Reads characters into STRING character array an array at address RECEIVE SELECT Read an input stringto astring As preceding but character array
238. mmended for engineering projects may need to be applied in the professional design environment Here some basic methods are outlined as a starting point these allow new applications to be developed with some degree of consistency and help communicate project concepts and design details clearly in reports and presentations Hardware Design The block diagram is an effective way to show the general form of a microcontroller application design and examples are seen throughout this book Some simple rules are used to represent system blocks and their input and output signals e The direction of signal flow is represented by an arrowhead e The TTL level digital signal is the default default arrow style e Other switching levels e g RS232 line are indicated by labels e The analog voltage range is indicated by a label and arrow style e Parallel data are represented by a block arrow e Analog signals are represented as a simple waveform 180 Part 5 Analo Pi Text Box with Parallel Data Output Functional 0 Vm Description gt Single TTL Output Figure 5 1 Block Diagram Conventions The block diagram Figure 5 1 is easily constructed using only the drawing tools in a standard word processor The example in Figure 5 1 might represent an analog to digital converter chip with an end of conversion output Once a block diagram has been created defining the inputs and outputs of each block a circuit sch
239. n setup_lcd LCD_MUX14 0 for n 0 n lt 11 n 2 1 ab Both bits 1 1 Decimal point 1 Decimal point 2 1 lcd _ symbol DigMap n DIG1 delay_ms 300 for n 0 n lt 11 n lcd _ symbol DigMap n DIG2 delay_ms 300 for n 0 n lt 11 n lcd _ symbol DigMap n DIG3 delay_ms 300 lcd_symbol1 0X80 1 delay_ms 1000 lcd_symbol1 0X00 1 lcd_symbol 0XFF 1 delay_ms 500 lcd_symbol1 0X00 1 lcd_symbol 0XFF 1 delay_ms 500 1lcd_symbol 0X00 1 lcd_symbol 0XFF 1 delay_ms 500 DIG4 DIG4 DP1 DP1 DP2 DP2 DP3 lcd_symbol1 0X00 1 while 1 DP3 Decimal point 3 Initialize 14 pin LCD no clock divide Display numerals 0 9 at digit 1 Send digit bits to segment addresses Display numerals 0 9 at digit 2 Send digit bits to segment addresses Display numerals 0 9 at digit 3 Send digit bits to segment addresses Switch on MSD digit 4 Switch off MSD digit 4 Switch on decimal point 1 Switch off decimal point 1 Switch on decimal point 2 Switch off decimal point 2 Switch on decimal point 3 Switch off decimal point 3 Done C Mechatronics Applications 151 Table 4 6 Bit Maps for LCD Numerals Numeral Segment A B C D E F G LSB Code Bit 7 6 5 4 3 2
240. n and setup_adc_ports allows the mix of analog and digital inputs to be defined using the combinations provided in the header file C Peripheral Interfaces 103 Listing 3 2 Test Program for Voltage Measurement VOLTS C MPB 25 3 07 Read amp display 10 bit input voltage KREKKEREKEKKER REE KR EKR EEE REE ERE RRR KEE EKER ERE REE ER ERR EER ERE REREREERERREEEE include 16F877A h device ADC 10 10 bit operation use delay clock 4000000 use rs232 baud 9600 xmit PIN_DO rcv PIN_D1 void main RRR EERE RE ERE RR EKER ERE REE RR RER ER kkk kkk kk ERE int chan float analin 8 disvolts 8 Array variables setup_adc ADC_CLOCK_INTERNAL ADC Clock source setup_adc_ports ANO_AN1_AN2_AN4_AN5_AN6_AN7_VSS_VREF ADC inputs while 1 Loop always for chan 0 chan lt 8 chan Read 8 inputs delay_ms 1000 Wait 1sec set_adc_channel chan Select channel analin chan read_adc Get input disvolts chan analin chan 400 Scale input putc 254 putc 1 delay_ms 10 Clear display print t Sd 4 3g chan disvolts chan Display volts J Table 3 1 CCS C Analog Input Functions Action Description Example ADC SETUP Initialize ADC setup_adc ADC_CLOCK_INTERNAL ADC PINS SETUP Initialize ADC pins setup_adc_ports RAO_ANALOG ADC CHANNEL SELECT Select ADC input set_adc_channel 0 ADC READ Read analog input inval re
241. n Specification The starting point for an electronics design is a specification which should state clearly the system performance requirements Our example project is called BAR1 Figure A 1 204 Appendix A Run MCU x8 Button Bar Graph 4MHz Figure A 1 BAR1 System Block Diagram This is used as the project folder name and the file name for the project files The specification is as follows When a button is pressed the system generates an 8 bit binary count starting at 0 on a bar graph display The output frequency at the least significant bit is 50 Hz giving an overall cycle time of 2 56 sec This specification could be elaborated by for example requiring a battery supply In that case an LCD display would be preferred for its low power consumption over the LED display used in the prototype A block diagram is useful for clarifying the hardware design The function of each main circuit block should be identified as well as the signals in and out In digital circuits the polarity of the signal can be indicated Run active low input and a parallel output represented with a block arrow x8 8 bits The standard word processor has all the drawing tools needed to create simple block diagrams Schematic Circuit The circuit in Figure A 2 shows a PIC 16F877A with crystal clock push button input and 8 bit bar graph display The output increments when the button is pressed using t
242. n arithmetic or logic operation is not zero bit 1 DC Digit carry borrow bit ADDWF ADDLW SUBLW SUBWF instructions for borrow the polarity is reversed 1 Acarry out from the 4th low order bit of the result occurred o No carry out from the 4th low order bit of the result bit O C Carry borrow bit ADDWF ADDLW SUBLW SUBWF instructions 1 Acarry out from the Most Significant bit of the result occurred o No carry out from the Most Significant bit of the result occurred Note For borrow the polarity is reversed A subtraction is executed by adding the two s complement of the second operand For rotate RRF RLF instructions this bit is loaded with either the high or low order bit of the source register Figure B 4 PIC 16F877 Status Register Bit Functions by permission of Microchip Technology Inc BAR1 List File The list file BAR1 LST in Listing B 3 shows the assembly language version of the program produced by the compiler This book does not assume knowledge of assembler programming but for those readers who have followed the usual progression from assembler the list file gives a useful insight into how the compiler works Comments italics have been added to the original file to explain its operation The original source code is highlighted in bold The compiler initially sets the memory page to 0 by loading the PCLATH program counter latch high register 0A with 0 This is the reset default setting anyway
243. n to escape from an endless loop caused by a program bug or run time condition not anticipated by the 10 Part 1 software designer To maintain normal operation the WDT must be disabled or reset within the program loop before the set time out period has expired It is therefore important to set the MCU configuration bits to disable the WDT if it is not intended to use this feature Otherwise the program is liable to misbehave due to random resetting of the MCU Power up Timer The power up timer PuT provides a nominal 72 ms delay between the power supply voltage reaching the operating value and the start of program execution This ensures that the supply voltage is stable before the clock starts up It is recommended that it be enabled as a precaution as there is no adverse effect on normal program execution Oscillator Start up Timer After the power up timer has expired a further delay allows the clock to stabilize before program execution begins When one of the crystal clock modes is selected the CPU waits 1024 cycles before the CPU is enabled Brown out Reset BoR It is possible for a transitory supply voltage drop or brown out to disrupt the MCU program execution When enabled the brown out detection circuit holds the MCU in reset while the supply voltage is below a given threshold and releases it when the supply has recovered In CCS C a low voltage detect function triggers an interrupt that allows the program to be re
244. nating the program Normally the program runs in a continuous loop but if not the final statement should be while 1 which causes the program to wait and prevents the program running into undefined locations following the application code C Programming Essentials 61 Listing 2 11 Comparison of Switch and If Else Control SWITCH C Switch and if else sequence control Same result from both sequences 11 11 1 1 1 1 1 1 11 11 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1111 1111 include 16F877A h void main int8 inbits while 1 inbits input_D Read input byte switch inbits Test input byte case 1 output_C 1 Input 0x01 output 0x01 break Quit block case 2 output_C 3 Input 0x02 output 0x03 break Quit block case 3 output_C 7 Input 0x03 output 0x07 break Quit block default output_C 0 If none output 0x00 if input PIN_DO output_C 1 This block has same effect if input PIN_D1 output_C 2 if input PIN_DO amp amp input PIN_D1 output_C 7 else output_C 0 We have already seen built in functions such as input PIN_DO and output_C 255 which read and write the ports Function arguments given in the parentheses allow function parameters to be passed to the function block in this case specifying the port or pin to be accessed Another example is delay_ms 100
245. nce of characters is significant to the compiler However in practice the program source code should be arranged to make it as easy to understand as possible Spaces or tabs can be used to indent each block program level and the open and close braces should be lined up in the same column so that the brace pairs can be matched up when www newnespress com 40 Part 2 checking the program This makes subsequent source code debugging and modification easier The benefits of good layout become more obvious later when more complex programs are developed By tradition C source code is written mainly in lower case with upper case used for certain key words 2 2 PIC16 C Program Basics e Variables e Looping e Decisions The purpose of an embedded program is to read in data or control inputs process them and operate the outputs as required Input from parallel serial and analog ports are held in the file registers for temporary storage and processing and the results are output later on as data or a signal The program for processing the data usually contains repetitive loops and conditional branching which depends on an input or calculated value Variables Most programs need to process data in some way and named variables are needed to hold their values A variable name is a label attached to the memory location where the variable value is stored When working in assembly language a register label acts as the variable name and has
246. nd further details are provided in Appendices A B and C Briefly the program project is created as follows 1 Assuming that MPLAB and CCS C compiler are installed create a folder for the project files and an MPLAB project called OUTNUM Copy the MCU header file 16F877 h from the CCS header file folder to the project folder 2 Write the program OUTNUM C in the source code edit window of MPLAB referring to the compiler manual for the correct syntax and save it in the project folder Assign the source code and header file in the project window 3 Build the project compile and link all files to create OUTNUM COF Correct any syntax and linker errors 4 Run the program in MPSIM simulation mode Use the source code debugging window to trace the program execution and the watch window to track the CPU variables Correct any logical errors 5 Optionally the program can be tested in Proteus VSM which once installed can be selected from the debugger menu C Programming Essentials 37 satire DB Pretenstonal OIE ye Eee VYOEReowrofuni Pr in he oa D amp A a Figure 2 1 ISIS Dialog to Attach the Program Program Testing The program could be tested by downloading to a suitable hardware target system but it is preferable to debug it first in simulation mode either in MPLAB or preferably in Proteus VSM In the VSM schematic capture and cosimulation module ISIS the
247. ng the PC screen on a projector teachers note the text can be enlarged for better visibility PIC CPU variables are displayed from the Debug menu Right click on the window and deselect the Globals option leaving just the program variables visible The display numerical format can then be changed by right clicking on the variable in the window for example to display the variables as unsigned integers if only positive whole numbers are used The CPU registers may be displayed if required as well as the CPU data memory that is the file registers Some of these have special or system functions the rest are available for variable storage Remember that some variable types use more than one location www newnespress com 224 Appendix C for example a 16 bit integer uses two The variable locations are highlighted when they change during single stepping If you need to slow down the program execution go to the System Animation options The Frames per Second and Timestep per Frame settings control the simulation speed The default settings are 20 f s and 50 ms f giving 20 X 50 1000 ms sec or real time If the Timestep per Frame is reduced to say 5 ms the simulation slows down by a factor of 10 This allows the system operation to be observed at a more leisurely pace in Run mode In complex applications the simulation may slow down automatically to allow the processor to complete the circuit solution for each simulation step in
248. ns and Systems 195 5 5 PIC16 C System Design e Hardware selection e Software design e System Integration We have seen how to get started with building PIC microcontroller systems programmed in C Simple examples have been used to illustrate the basic principles so we now need to look at some issues relating to more complex microcontroller based systems Numerous texts are available written by experienced and knowledgeable engineers that discuss the finer points of real time system design so the intention here is to introduce the some basic concepts to help the reader to move toward a further understanding of real industrial applications Another objective of this section is to review some relevant factors in the selection of the best combination of hardware programming language and development tools for any given microcontroller product design Hardware Selection There is a range of related devices around which embedded systems may be designed including a e Microcontroller MCU e Microprocessor CPU e System on a chip SoC The conventional microprocessor system embodies the traditional approach where a central processing unit memory and peripherals can be put together to meet the requirements of a particular application as precisely as possible Designing a custom made CPU system is a relatively expensive option and such an extensive range of other options are available that the conventional CPU based system may be neede
249. nt is 999 1998 pulses which takes about 20 sec to reach assuming the motor is running at about 3000 rpm The program source code is given in Listing 4 6 and is outlined in Listing 4 7 C Mechatronics Applications 155 Listing 4 6 Program to Display Motor Revs TITISTITTITI TTI TT TTI TTI TTT TIT TATI TT I ATTA T TT I ATA TI TT I ATTA TI A IT TT T MOTREVS C Program to count motor revs PICDEM hardware Connect SW2 RA4 RD4 N2 RD7 P1 TITITTITTITITTTTT TTI TIA TATT ATTA TTT TTI include 16F917 h include lcd inc Include file with LCD data use delay clock 8000000 void main 1 1 11111TTIITTTITTTTTTSATTAT TATA TTT TTA AAA TTT int8 BCD1 0 BCD2 0 BCD3 0 Initialize 3 digits int8 huns 0 tens 0 ones 0 and digit values int16 count 0 Receives timer count setup_lcd LCD_MUX14 0 Initialize 14 pin LCD setup_timer_1 T1_EXTERNAL Initialize rev counter while 1 Main loop start while input PIN_A4 Wait for switch 2 on delay_ms 10 Debounce switch COUNT MOTOR REVSX2 1111 11 11 1 11111111 71 set_timer1 0 Reset counter output_D 0x90 Start motor while input PIN_A4 Wait while switch on delay_ms 10 Debounce switch output_D 0x00 Motor off count get_timer1 Read counter count count 2 2 pulses per rev CONVERT COUNT TO BCD 1 11 1 1 11111111 7 huns tens ones 0 Reset digit values w
250. nter file registers and working register State the function of the following registers in the PIC16F877 02h 03h 09h 89h 20h Explain the significance of the following abbreviations in relation to the configuration of the PIC microcontroller RC XT WDT PUT NOWRT Explain the function of the following elements of the PIC I O circuit tristate gate current driver data direction latch input data latch output data latch A 16 bit PIC hardware timer is driven from the internal clock signal and the MCU is operating with a 20 MHz crystal Calculate the preload value required to produce an interrupt every 10 ms If an analog to digital converter has a positive input reference voltage of 2 048 V and is set up as for 8 bit conversion calculate the resolution of the ADC in millivolts per bit and the output code if the input voltage is 1 000V Refer to Figure 1 9 and briefly explain the timer interrupt process and why it is useful Sketch the RS232 signal that transmits the character X ASCII code 01011000 on a line operating at 12V Indicate the stop and start bits as S and P Explain the difference between an asynchronous and synchronous data transmission by reference to RS232 and SPI Explain the difference between hardware and software addressing as used by SPI and PC 32 Part 1 15 Explain briefly why SPI is generally faster than IC 16 A page of plain text contains about 1000 ASCII characters Estimate the m
251. odes for the LCD are preceded by the code 254 See the figure o Select Next Row Yes Read Columns N e Key pressed gt Make key code e a RETURN The function prints formatted output This means that any variable output has an associated formatting code such as d which determines how the value is interpreted The main options are signed integer floating point decimal or ASCII character The variable anum in this case is an array variable the element being output is numbered n Ampersand amp is the address_of operator which causes the memory address of the named variable to be returned The pointer is the contents of operator which returns the value of the contents of the location corresponding to the variable value 262 Answers 20 include means copy another source code file into the user source code define instructs the compiler to replace the given text with the given value use means include a library function device defines the target MCU and optionally an operating mode asm indicates the start of an assembly language sequence Assessment 3 1 setup_adc_ports AN0 Reference 5V resolution 5 1024 4 88 mV bit Resolution 4 096 1024 4 00 mV bit conversion factor 0 004 a float volts input b volts input 0 004 enable_interrupts int_AD enable_interrupts global int_AD void isrADC Using the ADC
252. ogram memory areas 258 Answers 10 11 12 13 14 15 Tristate gate data switching circuit allows data through only when enabled otherwise output is high impedance Current driver provides extra current on a loaded data line Data direction latch stores the bit that sets the port bit as input or output Input data latch stores the incoming bit when the port line is set to input Output data latch stores the outgoing bit when the port line is set to output 20 MHz clock 5 MHz instruction clock 200 ns period 10ms 10 000 000 ns Timer count required 10 000 000 200 50 000 instruction clock cycles Maximum count of 16 bit timer 65 536 Preload value 65 536 50 000 15 536 Resolution 2048 256 8mV per bit Output 1000 2048 xX 256 125 0 64 32 16 8 4 0 1 0111 1101 The timer interrupt is set up at the beginning of the program The timer is started at some point in the program and runs concurrently with program execution When a time out occurs the program is suspended and the interrupt service routine carried out The program is then resumed at the original point Interrupts allow the timer to independently generate an accurate interval between the timer start and interrupt request See the figure Ide S 0 0 0 1 140 0 P Idle fav RS232 is asynchronous in that it has no separate clock signal Instead the reception is re
253. on and push button frequency adjustment The DAC0808 produces a current output that needs an external amplifier to convert it to a voltage and provide the output drive The amplifier stage also allows the output amplitude and offset to be adjusted 128 Part 3 Listing 3 12 EEPROM Test Program EEPROM C Internal data EEPROM test design file EEPROM DSN include 16F877A h use delay clock 4000000 void main 1IISIISTSTSTTTTTTTTTTTTTTTTTAT TTT ATTA AAA TTT int writebyte readbyte int maxadd address port_b_pullups 1 Enable Port B internal pull ups if input PIN_C1 Write memory sequence address 0 First address do while input PIN_CO Wait for button writebyte input_B Get switch bank data write_eeprom address writebyte Write data to EEPROM readbyte read_eeprom address Read it back output_D readbyte Display data on bar graph while input PIN_CO Wait for button release address Next EEPROM address while writebyte 0 Continue until data 00 else Read memory sequence address 0 First address do while input PIN_CO Wait for button readbyte read_eeprom address Read data output_D readbyte Display it on bar graph while input PIN_CO Wait for button release address Next address while readbyte
254. on the MCU registers All the hardware information needed for programming in assembler is given in the data sheet for each PIC MCU including the instruction set register details and setup requirements A simplified version of the instruction set is shown in Table 2 11 It is organized by function that is instructions with similar functions are grouped together As explained in Part 1 the operation of the MCU revolves around the numbered file register set and the working register designated W in the instructions Register OC 124 the first general purpose register is used to represent the file registers in the examples The special function registers at the low addresses which control the MCU setup and program execution are accessed in exactly the same way as the data registers The Move instructions are the most commonly used these allow a data byte to be moved from the working register to a file register and back or to load immediate data into W Note that data cannot be moved directly between file registers in the 16FX XX instruction set this is one of the casualties of the minimal instruction set RISC chip design philosophy The register instructions operate on a single file register allowing it to be cleared incremented decremented rotated shifted and so on Individual bits may also be set and cleared The Arithmetic and Logic instructions operate on pairs of registers in binary adding subtracting and carrying out logical
255. ontrol statement for This unconditional for statement is equivalent to while 1 the unconditional while loop The main loop processes the input and calculates the resulting digits 2 7 PIC16 C More Data Types e Arrays and strings e Pointers and indirect addressing e Enumeration 74 Part 2 The data in a C program may be most conveniently handled as sets of associated variables These occur more frequently as the program data becomes more complex but only the basics are mentioned here Arrays Arrays are sets of variable values having the same type and meaning For example each word in a text file is stored as a character array a sequence of ASCII codes This is also referred to as a string A numerical array might be a sequence of voltage readings from an analog input in a test system or controller The program ARRAYS C Listing 2 18 shows how they can be created and displayed The arrays are declared using a collective name Listing 2 18 Numerical and Character Arrays ARRAYS C Demo of numerical and string arrays Attach ARRAYS COF to LCD DSN to display TITTITITTIAI TTT AAT AAT TTA ATTA AAT AAT AAA TTT include 16F877A h use delay clock 4000000 use rs232 baud 9600 xmit PIN_DO rcv PIN_D1 main int8 aval 0 n Declare single variables int8 anum 10 Declare integer array char astring 16 Declare character array I Start UCD e 4te sooo i ek el os oh ee oe eee BY del
256. p afloat sint is a signed integer random sequence RAISE TO Raise float toa powres Returns a float raised POWER power pow afloat apower to a power SQUARE ROOT Calculate the square sqrres Returns positive root root of a float sqrt afloat RANDOM Generates a anyl rand Returns a random NUMBER pseudorandom integer from sequence number RANDOM SEED Start value for the srand seed seed Is a new start point in the sequence Table F 12 Trigonometric Functions IN CCS C Program Function Reference 251 CLUDE MATH H Function Description Example Comment SIN Sine function numl sin a Returns sine of angle a given in radians cos Cosine function num2 cos a Returns cosine of angle a given in radians TAN Tangent function num3 tan a Returns tangent of angle a given in radians ASIN Arc sine function angl asin n Returns the angle in radians whose sine Is float n ACOS Arc cosine function ang2 acos n Returns the angle in radians whose cosine is float n ATAN Arc tangent function ang3 atan n Returns the angle in radians whose tangent is float n SINH Hyperbolic sine function hyp1 sinh x Returns hyperbolic sine of float x COSH Hyperbolic cosine hyp2 cosh x Returns hyperbolic cosine of function float x TANH Hyperbolic tangent hyp3 tanh x Returns hyper
257. pare succeeds Generate an interrupt when compare succeds Reset timer to zero when compare succeeds Enable Pulse Width Modulation mode Addresses of CCP1 registers Addresses of CCP2 registers TITTITTTTTTITTTTTT TATA TT AAT TTT TT ATT TATA TTT TATA I TT I TTT TTI TTT PSP PSP Functions SETUP_PSP PSP Variables PSP_OVERFLOW PSP_DATA Constants used in SETUP_PSP are PSP_ENABLED define PSP DISABLED define byte PSP_DATA 0x10 0 8 PSP_INPUT_FULL PSP_OUTPUT_FULL INPUT_D OUTPUT_D Enable Parallel Slave Port Disable Parallel Slave Port Address of PSP data register C Programming Essentials 83 ee SPI Functions SETUP_SPI SPI_WRITE SPI_READ SPI_DATA_IN Constants used in SETUP_SSP are define SPI_MASTER 0x20 Select SPI master mode define SPI_SLAVE 0x24 Select SPI slave mode define SPI_L_TO_H 0 Strobe data on rising edge of clock define SPI_H_TO_L 0x10 Strobe data on falling edge of clock define SPI_DIV_4 0 Master mode clock divided by 4 define SPI_CLK_DIV_16 1 Master mode clock divided by 16 define SPI_CLK_DIV_64 2 Master mode clock divided by 64 define SPI_CLK_T2 3 Master mode clock source Timer2 2 fine SPI_SS_ DISABLED 1 Slave select input disabled define SPI_SAMPLE AT END 0x8000 define SPI_XMIT_L_TO_H 0x4000 TITTITTTTTTITTTTTT TATA TT AAT TATA TT
258. play needs only 25 bits and ten of the available segment outputs SEGO 1 2 3 6 11 16 21 22 and 23 These outputs are encoded to allow individual bit control within the program LCD Test Program Listing 4 3 shows a test program LCD1 which displays the numerals 0 to 9 on each digit in turn then flashes on the MSD and three decimal points so that correct operation of each can be checked Listing 4 3 Test Program for Mechatronics Board LCD LCD1 C MPB 20 4 07 Test program for mechatronics board LCD Displays count 0 to 9 on Digits1 2 3 and 1 on Digit4 include 16F917 h use delay clock 8000000 LCD DISPLAY DATA 3 numerals 7 segments MSD 1 segment 3 decimal points Bit map for numerals 0 9 and blank ee eee Numeral 0 1 2 3 4 5 6 7 8 9 blank byte const DigMap 11 0xFD 0x60 0xDB 0xF3 0x66 0xB7 O0xBF 0xE0 0xFF 0xE7 0x00 Bit addressess in LCD RAM locations LCDDATAO to LCDDATA11 12 8 bits Numbered 0 95 with offsets COM0 0 COM1 24 COM2 48 COM3 72 Segment A B Cc D E F G define DIG1 COM0 22 COM0 23 COM2 23 COM3 22 COM2 22 COM1 22 COM1 23 Bit addresses define DIG2 COM0 6 COM0 21 COM2 21 COM3 6 COM2 6 COM1 6 COM1 21 Bit addresses define DIG3 COM0 3 COM0 11 COM2 11 COM3 3 COM2 3 COM1 3 COM1 11 Bit addresses 150 Part 4 define DIG4 COM2 define DP1 COM3 2 define DP2 COM3 1 define DP3 COM3 2 void main int8
259. ple Move Move data from F to W MOVF OC W Move data from W to F MOVWF OC Move literal into W MOVLW Register Clear W reset all bits and value to 0 CLRW Clear F reset all bits and value to 0 CLRF Oc Decrement F reduce by 1 DECF oc Increment F increase by 1 INCF oc Swap the upper and lower four bits in F SWAPF oC Complement F value invert all bits COMF oc Rotate bits Left through Carry Flag RLF oc Rotate bits Right through Carry Flag RRF Oc Clear reset to 0 the bit specified e g bit 3 BCF 0c 3 Set to 1 the bit specified e g bit 3 BSF 0c 3 Arithmetic Add W to F ADDWF oc Add F to W ADDWF OC W Add Lto W ADDLWOF9 Subtract W from F SUBWF oc Subtract W from F placing result in W SUBWF OC W Subtract W from L placing result in W SUBLWOF9 Logic AND the bits of W and F result in F ANDWF OC AND the bits of W and F result in W ANDWF OC W AND the bits of L and W result in W ANDLWOF9 C Programming Essentials 91 Table 2 11 Continued Operation Example OR the bits of W and F result in F IORWF oc OR the bits of W and F result in W TORWF 0c W OR the bits of Land W result in W IORLWOF9 Exclusive OR the bits of W and F result in F XORWF OC Exclusive OR the bits of W and F result in W XORWF 0c W Exclusive OR the bits of Land W XORLWOF9 Test and Skip Test a bit in F and Skip next instruction if it is Clear 0 BTFSC 0c 3 Test a bit in F and Skip nex
260. present only a limited range of numbers with a precision of 0 5 Therefore the floating point FP type should be used for many calculations particularly those with a fractional result The 32 bit FP format can represent decimal numbers from about 107 to 10 38 with a precision of about 10 7 0 0000001 The number is stored in exponential format as used in a standard calculator Twenty three bits are used for the significant digits called the mantissa Eight bits are used for the exponent part and one 50 Part 2 for the sign The IEEE standard form has the sign bit as the MSB but Microchip and CCS use a slightly more logical form where the sign bit is the MSB of the third byte leaving the exponent to be represented by the complete high byte Table 2 3 The significant figures of the floating point number mantissa are represented by a positive fractional binary number whose value is between 0 and 1 As in any binary number the weighting of the 23 bits is a power of 2 series but fractional that is 1 2 4 Ys Yo Y32 V64 2 The final fraction represents the resolution of the format that is the smallest step in the number sequence 1 273 1 8388608 0 0000001 107 Hence 32 bit floating point numbers are precise to about seven decimal places The final result can therefore be quoted to six decimal places assuming that rounding errors are not significant An example of a floating point number is given in Table
261. pt int_timer0O defined in device header file INTERRUPT Enables peripheral enable_interrpts Interrupt labels ENABLE interrupt int_timer0 defined in device header file INTERRUPT Clears peripheral clear_interrupt Interrupt labels CLEAR interrupt int_timer0O defined in device header file INTERRUPT Checks if interrupt flag interrupt_active Interrupt labels ACTIVE is set int_timer0O defined in device header file INTERRUPT Selects interrupt trigger ext_int_edge Rising L_TO_H or EDGE edge H_TO_L falling H_TO_L edge INTERRUPT Jump to address of ISR jump_to_isr Use to service multiple JUMP isr_loc interrupts Table F 19 Memory Read and Write Function Description Example Comment READ RAM Read a RAM abyte Alternative variable BANK location directly read_bank 3 0x20 access WRITE RAM Write a byte into write_bank Write to bank 3 BANK user RAM 3 0x20 0xFF address 0x20 data OxFF AD DATA Read an EEPROM abyte Get byte at given location read_eeprom 0x00 address R E WRITE DATA EEPROM Write a byte into EEPROM write_eeprom 0Ox1F 0x9A Write to nonvolatile memory address data READ PROGRAM ROM Read code from program ROM read_program_ memory 0x100 copy 4 Get block from program address copy in RAM CCS C Program Function Reference 255 T
262. put LSB flashes at 4 Hz Predict the frequency of the MSB and measure it using the simulation clock Assignment 2 2 Download the SIREN project files and check that the SIREN program in Listing 2 7 works correctly Modify the program to produce a default output at 1 kHz Further modify the program so that the output frequency is halved each time the input button is pressed C Programming Essentials 97 Assignment 2 3 Download the CALC project files and check that the CALC program works correctly Modify the program such that the ON C key must the pressed to start the program and pressing it again disables the program Investigate the use of the string processing functions to provide a more elegant implementation of the conversion of an input string of numbers to decimal during the input phase Outline how the program could be developed to handle floating point numbers to provide a more practical calculator C Peripheral Interfaces 3 1 PIC16 C Analog Input e Analog input display e Voltage measurement e ADC setup codes A microcontroller analog input allows an external voltage to be converted to digital form stored and processed This type of input occurs in data loggers control systems digital audio and signal processors to mention just a few The dsPIC range is designed specifically for high speed analog signal processing Analog Setup A basic setup to demonstrate analog input is shown in Figure 3 1 The PIC16F877 has eight
263. put and displayed as a decimal 65 because the formatting code is d The putc function outputs the ASCII code and displays the character A The UART data transfer takes about 1 ms during which time the MCU could be working on another task MCU utilization can be increased by using interrupts which can be set up to fire when the serial port has finished sending int_tbe or receiving int_rda a byte The interrupt service routines contain the code to write the next byte or read the next byte On return from interrupt a foreground task continues which is interrupted again only when the UART is ready for the next byte transfer Each slave sender needs a slave select line connected to the master MCU not to ground The master program contains bit switching statements to enable the select line of a slave MCU programmed to transmit i2c_start 12c_write 0xA0 i2c_write 0x01 i2c_write 0xFF i2c_write OxAA 1i2c_stop See the figure 5V PIC1 PIC2 SDA SDA Set up the PSP interrupt in the slave PIC Select the slave PIC by taking CS low 264 Answers 16 17 18 19 20 Present the data to the Port D data pins Take WR low to latch in the data Interrupt INT_PSP generated to read the port data The minimum number of wires is used by I C but the rate of transfer is reduced compared with SPI because control and address bytes have to be sent before the d
264. r file referred to in this case provides the information needed by the complier to create a program for a specific PIC chip use delay clock 4000000 The use directive allows library files to be included As can be seen additional operating parameters may be needed so that the library function works correctly The clock frequency given here needs to be specified so that both software and hardware timing loops can be correctly calculated use rs232 baud 9600 xmit PIN DO rcv PIN D1 In this directive the parameters set the RS232 data baud rate and the MCU pins to be used to transmit and receive the signal This software serial driver allows any available pin to be used Header File A selection of the more commonly used directives are seen in the processor header file which must be included in every program The file 16F877A H is reproduced in full in Listing 2 19 The device directive selects the target processor and can be followed by various options One that we use later is ADC 8 which sets the resolution of the analog input conversion C Programming Essentials 79 Listing 2 19 Header File 16F877A H Standard Header file for the PIC16F877A device device PIC16F877A 367 Stack 8 2000 WDT NOPUT PUT PROTECT DI TECT NOBROWNOUT BROWNOUT LVP NOLVP CPD NOCPD WRT_50 EBUG NOD EBUG TITIITTTTTTITTTTTT TAT T TTT TATA TTT TT TAIT TTT TT
265. r use as data RAM Note that the number of registers used for each C variable depends on the variable type and can range from 1 to 32 bits 1 4 GPRs Other PIC Chips In any embedded design the features of the MCU need to be matched to the application requirements The manufacturer needs to make sure that as applications become more demanding a more powerful device of a familiar type is available We can see this process at work where Microchip started out producing basic chips such as the 16C84 then developed the product range to meet the growing market PIC microcontrollers are currently available in distinct groups designated the 10 12 16 18 and 24 series Their general characteristics are outlined in Table 1 2 The original 16 series CMOS devices were designated as 16CXX When flash memory was introduced they became 16FXXX Currently a limited number of devices are 8 Part 1 Table 1 2 PIC Microcontroller Types MCU Pins Data Program Typical Speed Description Word Memory Instruction MIPS bits bytes Set Low pin count small form factor cheap no 10FXXX 6 8 512 33 X 12 bits lt 2 EEPROM no low power assembler program Low pin count small form 12Fxxx 8 8 lt 2 kB 12 14bits 0 5 factor cheap EEPROM 10 bit ADC some low power assembler Mid range UART 12C 16FXXX lt 64 8 lt 14 kB 35 X 14 bits 5 SPI many low power C or assembler program High range CAN USB 18FXXXX 100 8 128
266. re due to Gabe Hudson of Larrytech Internet Services for friendly maintenance and support I can be contacted at the e mail address martin picmicros org uk with any queries or comments related to the PIC book series Finally thanks to Julia for doing the boring domestic stuff so I can do the interesting technical stuff About the Author Martin P Bates is the author of PIC Microcontrollers Second Edition He is currently lecturing on electronics and electrical engineering at Hastings College UK His interests include microcontroller applications and embedded system design Introduction The book is organized in five parts Part 1 includes an overview of the PIC microcontroller internal architecture describing the features of the 16F877A specifically This chip is often used as representative of the 16 series MCUs because it has a full range of peripheral interfaces All 16 series chips have a common program execution core with variation mainly in the size of program and data memory During programming certain operational features are configurable type of clock circuit watchdog timer enable reset mechanisms and so on Internal features include the file register system which contains the control registers and RAM block and a nonvolatile EEPROM block The parallel ports provide the default I O for the MCU but most pins have more than one function Eight analog inputs and serial interfaces UART SPI and I C are brought out to spec
267. recisely this purpose to write operating systems for computers C interrupts are considered further in Section 3 2 and RTOS principles are outlined in Section 5 4 1 4 PIC16 Serial Interfaces e USART asynchronous link e SPI synchronous bus e 2C synchronous bus Serial data connections are useful because only one or two signal wires are needed compared with at least eight data lines for a parallel bus plus control signals The typical PIC Microcontroller Systems 19 PIC MCU HOST PC p Line J TX1 Transmit Driver g 12V RX2 RX1 Receive TX2 COM PORT Interface Ground L Ground Figure 1 10 USART Operation Bit Period ASETI Idle Start Bit Bit Bit Bit Bit Bit Bit Bit Stop Bit 0 1 2 3 4 5 6 7 Bit Figure 1 11 USART RS232 Signal PIC microcontroller offers a choice of serial interfaces The best one for any given communication channel depends on the distance between nodes the speed and the number of hardware connections required USART The universal synchronous asynchronous receive transmit USART device is typically used in asynchronous mode to implement off board one to one connections The term asynchronous means no separate clock signal is needed to time the data reception so only a data send data receive and ground wires are needed It is quick and simple to implement if a limited data bandwidth is acceptable A common application is connecting the PIC chip to
268. return outbyte Return output when loop stops main 11 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 111 11 1111111111 count 50000 out count Pass count value to function output_C outbyte Display returned value while 1 If an electronic gadget has a small alphanumeric LCD the chances are that it is a microcontroller application Smart card terminals mobile phones audio systems coffee machines and many other small systems use this display The LCD we use here has a standard serial interface and only one signal connection is needed The signal format is RS232 a simple low speed protocol that allows 1 byte or character code to be sent at a time The data sequence also includes start and stop bits and simple error checking can be applied if required The PIC 16F877 in common with many microcontrollers has a hardware RS232 port built in Further details of RS232 are found elsewhere in this book Serial LCD CCS C provides an RS232 driver routine that works with any I O pin that is the hardware port need not be used This is possible because the process for generating the RS232 data frame is not too complex and can be completed fast enough to generate 66 Part 2 the signal in real time At the standard rate of 9600 baud each bit is about 100 ps long giving an overall frame time of about 1 ms The data can be an 8 bit integer or more often a 7 bit ASCII character code This method of transferr
269. ridge Driver Control Logic States Inputs Outputs Result Drive State P mM N F Pg Ng X X X 0 1 0 Bridge disabled both off OFF 1 0 X 0 1 1 0 Bridge disabled default input OFF 2 1 1 0 1 0 0 Source on Sink off SOURCE 3 Xx 1 1 1 1 1 Source off Sink on SINK 4 1 0 X 1 0 0 Source on Sink off SOURCE 5 0 0 X 1 1 0 Bridge disabled both off OFF 6 Note Default input open circuit links is shown in bold C Mechatronics Applications 175 Assuming we start with all inputs open circuit and both FETs off the bridge is switched to the Source mode when the P input is taken high State 3 and to the Sink mode when N is taken high State 4 The Sink mode can be used to switch a load connected to the positive supply on and off or to provide single ended PWM drive For full bridge operation P1 and N2 P2 and N1 and M1 and M2 are linked via the six input links Drive 3 and 4 inputs are linked in the same way In this mode load current is bidirectional and can be reversed by toggling M with P and N high States 4 and 5 States 4 5 and 6 allow the bridge to be switched between Sink Source and Off Demo Applications The mechatronics board simulation represents fixed connections around the MCU by labeled terminals Additional connections can be made to uncommitted pins using the normal wiring tools in ISIS allowing the demo applications to be tested Note however that only the f
270. river that generates the required interface purely in software This means dedicated analog ports may not be necessary giving greater flexibility in the choice of MCU On the other hand the sensor is likely to be more expensive Program memory capacity requirements are not easy to anticipate before the software has been finalized C programs generally need more memory than assembler so the choice of language is important This factor is considered further later but for now suffice it to say that memory requirements expand rapidly with program complexity As regards RAM PIC16 C Applications and Systems 199 requirements the PIC is strictly limited as the only onboard RAM consists of spare file registers External data memory may well be necessary as in our data logger An alternative type of MCU could even be necessary for data intensive applications The PIC scores well on operating speed however The 16 series devices can generally run at 20 MHz with the 18 and 24 series running at 40 MHz The clock speed does affect the power consumption as the current consumed is proportional to the switching rate in CMOS devices Low power MCUs are an important ongoing development in microprocessor technology Reduced operating voltages e g 3 3 V supply are also increasingly used to reduce power dissipation Power consumption is not one of the operating parameters normally predicted by simulation so a real hardware prototype may be needed to f
271. rnal or external hardware events They are studied in more detail later in relation to programming peripheral operations However at this stage it is useful to have some idea about the interrupt options provided within the MCU Table 1 3 lists the devices that can be set up to generate an interrupt PIC Microcontroller Systems Table 1 3 Interrupts Sources in the PIC16F877 Interrupt Source Interrupt Trigger Event Interrupt Label 17 Timers TimerO TimerO register overflow INT_TIMERO Timer Timer1 register overflow INT_TIMER1 CCP1 Timer1 capture or compare detected INT_CCP1 Timer2 Timer2 register overflow INT_TIMER2 CCP2 Timer2 capture or compare detected INT_CCP2 Ports RBO INT pin Change on single pin RBO INT_EXT Port B pins Change on any of four pins RB4 RB7 INT_RB Parallel Slave Port Data received at PSP write input active INT_PSP Analog Converter A D conversion completed INT_AD Analog Comparator Voltage compare true INT_COMP Serial UART Serial Port Received data available INT_RDA UART Serial Port Transmit data buffer empty INT_TBE SPI Serial Port Data transfer completed read or write INT_SSP I C Serial Port Interface activity detected INT_SSP 12C Serial Port Bus collision detected INT_BUSCOL Memory EEPROM Nonvolatile data memory write complete INT_EEPROM The most effective way of integrating timer operations into an application program is by using a timer interr
272. rog Prog Prog Prog 002h count 082h count 102h count 182h count low low low low 003h Status reg 083h Status reg 103h Status reg 183h Status reg 004h File select 084h File select 104h File select 184h File select 005h ROTHA 085h ROITA 105h 185h data direction 006h Port B 086h Port B 106h Port B 186h Port B data direction data direction 007h Pere C 087h ponis 107h z 187h data direction 008h nea 088h ROD 108h 188h data direction 009h porni 089h poe 109h 189h data direction Prog Prog Prog Prog 00Ah count 08Ah count 10Ah count 18Ah count high high high high OOBh Interrupt 08Bh Interrupt 10Bh Interrupt 18Bh Interrupt control control control control 4 4 10Ch peripheral 18Ch peripheral 20 20 10Fh control 18Fh control 00Ch peripheral O8Ch peripheral registers registers 01Fh control O9Fh control registers registers 110h 16 general 190h 16 general eet purpose ou purpose registers registers Aonhe spate RTA P jhe pees Taone ET osFh PUP ogrh PHP 16Fh 1EFh PHP registers registers registers registers 16 ozon common oron Messe azon Mceses apon Ace 07Fh OFFh a 17Fh 3 1FFh 7 ae 07Fh 07Fh 07Fh s PIC Microcontroller Systems 7 RAM File Registers The main RAM block Table 1 1 is a set of 368 8 bit file registers including the special function registers SFRs which have a dedicated function and the general purpose registers GPRs When variables are creat
273. rogram Disassembler list file shows the assembler code generated from the C source code Output message shows the compiler status and errors Watch variable values monitored during program execution Host PC MPLAB development system C compiler programming module connectors target system with PIC MCU Assessment 2 1 Include header file using directive Main program statement block enclosed in braces TO functions sec within main Create MPLAB project Edit program using correct syntax Build program and correct syntax errors Test program in simulator and debug Optional test in cosimulation mode output_C 64 output_high PIN_C6 260 Answers 10 11 12 13 14 The WHILE loop tests the control condition before the loop statements are executed The DO WHILE tests after they have been executed at least once The FOR loop executes a loop a fixed number of times Port D bits initially go on for 1 sec If the switch is active the high 4 bits then go off and the program waits until the switch goes inactive at which point all the outputs go off If the switch is inactive all the LEDs go off after 1 sec a 255 b 32 767 c 2 1 273 x 2 8 6 8 x 10 a 8 bit precision 1 28 x 100 0 39 b 32 bit FP precision 1 277 x 100 0 000012 Mantissa 011 gt 0 25 0 125 0 375 1 375 Exponent 1000 0010 130 130 127 3 2
274. rom the right The most significant half digit 4 has only segments B and C displaying only 1 Four common connections COM1 COM4 enable groups of segments such that each has a unique address Note that this is a standard DMM display so additional symbols are available that are not needed in the mechatronics board applications The data for the display segments are stored in dedicated set of 12 registers in the PIC 16F917 Table 4 5 called LCDDATAx 148 Part 4 Table 4 5 PIC 16F917 LCD RAM Data Register Bits Address COMO Address COM1 00 06 03 24 Se buss s 03 ana LCDDATAO xx 2A xx XX 3A xx xx XX LCDDATA3 XX 2F xx xx 3F XX XX XX 08 ss a ss sa Tl ss se as 32 s gt G5 s J1 s LCDDATA1 XX XX XX XX 3B XX XX XX LCDDATA4 XX XX XX XX 3G XX XX XX 016 23 22 21 40 23 22 20 a aS eS LCDDATA2 1B 1A 2B XX XX XX XX XX LCDDATA5 1G 1F 2G xx xx xx XX XX Address COM2 Address COM3 48 06 03 02 72 06 lt 03 02 s LCDDATA6 xx 2E xx xx 3E 4x xx xx LCDDATA9 xx 2D xx xx 3D P3 xx xx 56 as Se Se Se Le Se eo 0e 35 5A Go SS 11 Ss Sen LCDDATA7 xx XX XX xx 3C xx xx xx LCDDATA10 xx xx xx xx P2 XX XX XX 64 23 22 21 gt BBF 22 21 eS S Soo Se LCDDATA8 1C 1E 2C xx xx xx xx xx LCDDATA11 xx 1D P1 xx xx xx xx xx where
275. s Alternative functions for the same operation putc putchar getc getch getchar output_bit PIN_XX 1 output_high PIN_XxX output_bit PIN_XX 0 output_low PIN_XX get_timer0 get_rtcc set_timer0 nnn set_rtcc nnn pow pwr 244 Appendix F Table F 1 Port Input and Output Requires Chip Header File Only e g 16F877A H Function Description Example Comment WRITE BYTE Write all bits with 8 bit output_A 255 A replaced by B C D integer orE SET BIT Write output bit high output_high AO replaced by A1 using pin label PIN_AO A2 A7 B0 B7 etc CLEAR BIT Write output bit low output_low AO replaced by A1 using pin label PIN_AO A2 A7 BO B7 etc READ BYTE Read input as 8 bit abyte A replaced by B C integer input_A D or E READ BIT Read input bit using abit AO replaced by A1 pin label input PIN_AO A2 A7 BO B7 etc READ DIRECTION Check port data ddra Any parallel port ddr direction register get_tris_a code can be checked CHECK BIT Read input bit abit Gets I O bit value input_state PIN_DO BIT TOGGLE Toggle output bit output_toggle Invert the logic level at PIN_DO the specified pin BIT OUTPUT Change port bit to output output_drive PIN_DO Does not change the existing bit value FLOAT OUTPUT Set output pin
276. s If the processor ignores the keyboard completely while downloading a large file from the Internet the user cannot access the system to do something more urgent In addition the OS has to be multitasking that is it must allow several operations to appear to be running simultaneously such as allowing you to keep writing while printing We also want to switch quickly between tasks by keeping more than one window open at a time which means keeping multiple tasks loaded in memory For example while running the examples in this book we need to have MPLAB and Proteus open at the same time plus maybe a data PDF and the word processor Multitasking is essentially achieved by time slicing Each apparently concurrent task is allowed to run for a given time interval say 100 ms then execution switches to another Priority can be assigned so that for example one Internet data packet is picked up and stored in memory before the next arrives and overwrites it in the network data buffer Therefore the OS is designed so that multiple tasks appear to run smoothly together and with the right priorities The PC is essentially a batch processing system that is the timing of the major tasks is not critical If a word processing task is delayed for a few milliseconds it is not apparent to the user and not significant in terms of overall system effectiveness On the other hand the timing of events in so called real time systems must generally be highly predi
277. s int_timer0 DISABLE INTERRUPT Enables peripheral interrupt enable_interrupts int_timer0 ENABLE INTERRUPT Checks if interrupt flag set interrupt_active int_timer0 ACTIVE INTERRUPT EDGE Selects interrupt trigger edge ext_int_edge H_TO_L INTERRUPT JUMP Jump to address of ISR jump_to_isr isr_loc C Peripheral Interfaces 105 and 3 4 These predefined labels must be used when enabling individual interrupts and declaring the ISR block They are defined in the header file along with the initialization codes for the interrupt control registers Table 3 3 16F877 Primary Interrupts Interrupt Label Interrupt Source GLOBAL Use to enable all interrupt sources INT_EXT External interrupt detect on RBO INT_RB Change on Port B detect INT_RTCC Timer 0 overflow same as TIMERO INT_TIMERO Timer 0 overflow same as RTCC Table 3 4 16F877 Peripheral Interrupts Interrupt Label Interrupt Source Ports INT_TBE USART transmit data done INT_RDA USART receive data ready INT_SSP Serial data received at SPI or I2C INT_BUSCOL 12C collision detected INT_PSP Data ready at parallel serial port Timers INT_TIMER1 Timer 1 overflow INT_CCP1 Timer 1 capture or compare detect INT_TIMER2 Timer 2 overflow INT _CCP2 Timer 2 capture or compare detect Others INT_AD Analog to digital converter complete INT_COMP Comparator outp
278. s or jump address The mid range PIC has a limited number of instructions 35 and is therefore classified as a RISC reduced instruction set computer processor Looking at the internal architecture we can identify the blocks involved in program execution The program memory ROM contains the machine code in locations numbered from 0000h to 1FFFh 8k The program counter holds the address of the current instruction and is incremented or modified after each step On reset or power up it is reset to zero and the first instruction at address 0000 is loaded into the instruction register decoded and executed The program then proceeds in sequence operating on the contents of the file registers 000 1FFh executing data movement instructions to transfer data between ports and file registers or arithmetic and logic instructions to process it The CPU has one main working register W through which all the data must pass If a branch instruction conditional jump is decoded a bit test is carried out and if the result is true the destination address included in the instruction is loaded into the program counter to force the jump If the result is false the execution sequence continues unchanged In assembly language when CALL and RETURN are used to implement PIC Microcontroller Systems Flash K ROM Program Counter 13 bits Program enon Address 8192 Xx 14 bits Stack RAM 13 bits File s x8 Registers In
279. s p Po 5 32 768Khz cerca MA eee Be a ORWE 2 wen BS 2 xz SWI MCLR La 29 Ps Ras u c16 O R2 l N oogt vzs nee gs onl eee 9 DOL ir od swe a connect tor eee acs i 4 Full Bridge R25 O ome gik ame ike ee ape WW orroa erur opg ua Pate SWS ae i RAS CLKING oe see RASCLKOUT OO eck ewe O A sacn e e mk ROS COPI PIA current sense R20 RC4 C20UT PIB R17 nal eee RCB ANT PIC A a mih reem css ara Cet me re O RC7 ANS SD0 CII ee Te r 2m umee S BE o rm Sear carat MOJO kiimas Figure 4 3 Mechatronics Board Layout by permission of Microchip Inc stages are connected as shown Pairs of FETs are switched on to allow the current to flow diagonally through FET1 and FET4 or FET3 and FET2 reversing the current in the load An additional control input allows PWM control of the drives This involves switching the current on and off over a set period and varying the average current by changing the mark space ratio The PIC has two CCP modules that use the internal hardware timers to provide the required output at CCP1 and CCP2 see Part 3 The DC motor needs some form of feedback if it is to be controlled accurately It therefore has a slotted wheel attached to its output shaft which passes between an LED and opto sensor The sensor produces a pulse for each slot two per revolution which allows the motor position and speed to be measured by the
280. s board has its main signals brought to in line connectors as shown in the board layout Figure 4 3 The components can be connected up for different applications using link wires The connector pin functions are listed for reference in Tables 4 1 through 4 4 Motor Drives The motors are driven from a set of four half bridge driver stages which can handle up to 1 A each These can be connected to the 5 V regulated or the 9 12 V unregulated supply for higher power output Note that the main plug supply may be rated at less than 1 A so a separate supply is advisable if the full drive current is needed Each driver has a pair of MOSFETs which allow the stage to source or sink current depending on which transistor is switched on Figure 4 4 Control logic prevents both coming on at the same time and shuts down all the drives if an overcurrent fault is detected This is activated on power up for fail safe operation and must be cleared manually before testing a motor If the DC motor needs to be driven in both directions the half bridge C Mechatronics Applications 139 POT1 gt 0 5V E ies emp POT2 gt J4 pins 3 4 Sensor gt 500mV J4 pin 1 Push Active Low Light 0 5V Switch gt J4 pins Sensor J4 pin 2 234 gt 678 PIC 16F917 MCU 32 768 kHZ 8 MHz XTAL Clock Reset SW1 IMCLR OSCI OSC2 S
281. se basic features is shown in SIREN C Listing 2 7 This program outputs to a sounder rather than an LED operating at a higher frequency 46 Part 2 Listing 2 7 SIREN Program Source code file SIREN C Author date version MPB 11 7 07 V1 0 Program function Outputs a siren sound Simulation circuit INBIT DSN Compiler CCS C Version 4 KRKKKKRKEK EKER EKER RRR KEK ERE EK KERR RHEE KEKE ER ERK ERE RE KR RE KKERERERKRKE REE K include 16F877A h use delay clock 1000000 void main int step while 1 Keep checking switch i while input PIN_CO Siren while switch ON for step 0 step lt 255 steptt Loop control output_high PIN_DO Sound sequence delay_us step output_low PIN_DO delay_us step The delay is therefore in microseconds The output is generated when the switch is closed input CO low The delay picks up the incrementing value of step giving a longer pulse each time the for loop is executed This causes a burst of 255 pulses of increasing length reducing frequency repeating while the input is on Note that 255 is the maximum value allowed for step as it is an 8 bit variable When run in VSM the output can be heard via the simulation host PC sound card Note the inversion of the input test condition using not true The header information is now more extensive as would be the case in a real application Generally the more complex a program t
282. set of numbers that are continuous as in ARRAYS C a convenient way is to use the enumeration variable type Figure 2 14 In its simplest form it assigns incrementing values to a set of labels Optionally the value can be set explicitly at any point in the list and the values increment from there Note that the label values are not initialized in the file registers just created in the complier memory In the example ENUMER C illustrated the value of label mar 03 only appears in memory at address 0x21 when assigned to the integer variable month 2 8 PIC16 C Compiler Directives e Include and use directives e Header file listing and directives www newnespress com 78 Part 2 Compiler directives are typically used at the top of the program to set up compiler options control project components define constant labels and so on before the main program is created They are preceded by the hash symbol to distinguish them from other types of statements and do not have a semicolon to end the line Program Directives Examples using the directives encountered thus far follow tefer to the compiler reference manual for the full range of options include 16F877A h The include directive allows source code files to be included as though they had been typed in by the user In fact any block of source code can be included in this way and the directive can thus be used to incorporate previously written reusable functions The heade
283. source up to 25 mA at 5 V or whatever the supply voltage is 2 6 V A data 0 allows the pin to sink a similar current at OV PIC Microcontroller Systems 13 Write TRIS bit gt Data a Tristate Output Enable CPU Data Bus Output 5 Current Write Data bit Driver Read Data bit Analog Input q Multiplexer Figure 1 4 I O Pin Operation The 16F877 has the following digital I O ports available Port A RAO RA5 6 bits Port B RBO RB7 8 bits Port C RCO RC7 8 bits Port D RDO RD7 8 bits Port E REO RE2 3 bits Total digital I O available 33 pins Most of the pins have alternate functions which are described later Timers Most microcontrollers provide hardware binary counters that allow a time interval measurement or count to be carried out separately from program execution For example a fixed period output pulse train can be generated while the program continues with another task The features of the timers found in the typical PIC chip are represented in Figure 1 5 but none of those in the 877 has all the features shown The count register most commonly is operated by driving it from the internal instruction clock to form a timer This signal runs at one quarter of the clock frequency that is one instruction takes four cycles to execute Therefore with a 4 MHz clock the timer counts in microseconds 1 MHz instruction clock The number of bits in the timer 8 or 16 14 Part
284. started in an orderly way Code Protection CP The chip can be configured during programming to prevent the machine code being read back from the chip to protect commercially valuable or secure code Optionally only selected portions of the program code may be write protected see WRT_X later In Circuit Programming and Debugging Most PIC chips now support in circuit programming and debugging ICPD which allows the program code to be downloaded and tested in the target hardware under the control of the host system This provides a final test stage after software simulation has been used to eliminate most of the program bugs MPLAB allows the same interface to be PIC Microcontroller Systems 11 used for debugging in both the simulation and in circuit modes The slight disadvantage of this option is that care must be taken that any application circuit connected to the programming ICPD pins does not interfere with the operation of these features It is preferable to leave these pins for the exclusive use of the ICPD system In addition a small section of program memory is required to run the debugging code Low Voltage Programming Mode The low voltage programming mode can be selected during programming so that the customary high 12V programming voltage is not needed and the chip can be programmed at V 4a 5 V The downside is that the programming pin cannot then be used for digital I O In any case it is recommended here that the
285. structions Levels 368 X 8 bits Instruction Register File Address Program Address SaaS a SS ES SS ee E A SS Se Se ee eee eS Working W File Select Literal Register Register i Arithmetic amp Logic Unit Status J bani 7 Status Flag ie Register Data Bus 8 bits v AA EEPROM Instruction gt MCU 256 bytes Decode amp m control CPU control gt lines Ports Timers A ADC Serial I O Timing control Zara Clock Reset N Y subroutines a similar process occurs The stack is used to store return addresses so that the program can return automatically to the original program position However this mechanism is not used by the CCS C compiler as it limits the number of levels of subroutine or C functions to eight which is the depth of the stack Instead a simple Port A B C D Figure 1 3 PIC16F877 MCU Block Diagram 5 GOTO instruction is used for function calls and returns with the return address computed by the compiler 6 Part 1 Table 1 1 PIC16F877 Simplified File Register Map Bank 0 000 07F Bank 1 080 OFF Bank 2 100 180 Bank 3 180 1FF Address Register Address Register Address Register Address Register 000h Indirect 080h Indirect 100h Indirect 180h Indirect 001h TimerO 08ih Option 101h TimerO 18ih Option P
286. synchronized by each start bit and reception is timed by a local clock SPI has a separate clock used to strobe each bit into the receiver generated from the master MCU clock and is therefore classed as a synchronous system SPI needs a hardware chip select signal connected to each slave which the master takes low to enable one slave receiver at a time I7C transmits the target address on the data line the slave must check all transmissions and pick up the data that follow its own address PC has to send addressing and control information as well as the data on the data line while SPI has hardware slave selection 16 17 18 19 20 Answers 259 RS232 9600 baud 10 k bits sec 1k bytes sec 1000 characters sec Page time 1 sec SPI 5 MHz clock 0 2 us bit 2 s character some loading delay Page time 2 ms C source code entered via a text editor HEX hexadecimal code machine code program COF downloading file that contains the hex code plus debugging information LST list file a text file containing source code hex code comments etc ERR error file that lists the error messages generated by the compiler Vs OV Vaa 5V supply connections Vpp programming voltage 14V MCLR Master Clear resets MCU PGD program data download PGC programming clock signal Project file shows the files used to make the project Source code edits window for entering p
287. t for n 1 n lt count n Use global value for count main 1 1 1 _ Main block count 2000 Set variable value out Call function while 1 Wait for reset J variables are used The function out runs a binary count which is stopped when a switch on pin DO is closed This value is then returned to the main program and displayed Variable n is local to function out and is declared within the function Variable t is also local but receives its value from the variable count in the calling routine The value is transferred between the argument in the function call count and the argument of the function declaration int16 t Note that the local integer type must be declared in the function declaration The function also returns a value outbyte to the main block This is displayed at Port C in the main routine 2 6 PIC16 C Input and Output e RS232 serial data e Serial LCD e Calculator and keypad C Programming Essentials 65 Listing 2 14 Using Local Variables in Functions FUNC3 C Uses local variables 1 111 11 11 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 11 1 1 1 1111 1111111 include 16F877A H int8 outbyte 1 Declare global variables int16 count int out int16 t Declare argument types int16 n Declare local variable while input PIN_DO Run at speed t outbyte for n 1 n lt t n
288. t including PWM SPI PC UART USART string manipulation and math libraries e Full user level control over data and code memory allocation It must be assumed that the integration of C18 into the MPLAB IDE will be reasonably seamless giving it a built in advantage over competing compilers Source level debugging in particular can reveal limitations in the effectiveness of the integration into the IDE of a third party product C Compiler Comparison 229 Relocatable object modules allow the user to build up a library of reusable routines This is obviously useful when producing a series of similar application programs If particular hardware peripherals are used repeatedly in different designs the same driver routines perhaps with minor variations can be used However these routines must be designed to receive and return variable values in a consistent manner to maximize the benefits of this approach Library routines are provided for the main peripheral interfaces and a comprehensive selection is found in the C 8 Compiler Libraries manual Software drivers allow peripherals to be connected to any pin not just those associated with the internal hardware interface This provides more flexibility in the use of the chip pins and may mean that a cheaper device can be used for a particular application If we look at some source code examples provided in the C78 User Guide we may be able to identify some of the features where C18 an
289. t numl A a aa from integer 0 Complement Invert all result num1 0101 0010 0 bits of 01 integer Arithmetic operation Add Integer or result numl num2 0000 1010 0001 float 0000 01 000 Subtract Integer or result numl num2 0000 1010 0000 float 0000 00 0 Multiply Integer or result num1 num2 0000 1010 0001 float 0000 00 1110 Divide Integer or result num1 num2 0000 1100 0000 float 0000 00 0100 Logical operation Logical AND amp Integer result numl amp num 2 1001 0011 000 bitwise amp 0 000 000 LogicalOR Integer result num1 num2 1001 0011 bitwise o 000 00 Exclusive OR Integer result num1 num2 1001 0011 0 bitwise 0 000 0010 Conditional Operations Where a logical condition is tested in a while if or for statement relational operators are used One variable is compared with a set value or another variable and the block is executed if the condition is true The conditional operators are shown in Table 2 7 Note that double equals is used in the relational test to distinguish it from the assignment operator C Programming Essentials 55 S opers MPLAB DE v7 50 Pie ESR View Projet Cebugger Programmer Tock Copre Window Hep Ose B GAM nesei s UGO F enot PteE int8 bytel 123 byte2 45 int8 addbyte sub
290. t contains a for loop to provide a delay so that the output count is visible This is a simple alternative to the built in delay functions seen in previous examples and is used here to avoid the inclusion of such functions while we study user defined functions It simply counts up to a preset value to waste time The delay time is controlled by this set value For those readers familiar with assembly language the disassembly listing for this program is instructive It will be seen that Call and Return are not used to implement the function call Instead Goto is used throughout this is to avoid the limited stack depth eight levels in the PIC architecture so that it is possible to have more that eight levels of function calls in the program C Programming Essentials 63 Listing 2 12 Basic Function Call FUNC1 C Function call and program structure 11 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 11 1111 include 16F877A H int8 outbyte 1 Declare global variables int16 n void out 1 1 1 1 _Start of function block while outbyte 0 Start loop quit when output 0 output_C outbyte Output code 1 OxFF outbyte Increment output for n 1 n lt 500 n Delay so output is visible H main 1 1 1 _ Start of main block out Function call while 1 Wait until reset Global
291. t instruction if it is Set 1 BTFSS 0c 3 Decrement F and Skip next Instruction if it is now 0 DECFSZ oc Increment F and Skip next Instruction if it is now 0 INCFSZ oc Jump Go To a Labeled Line in the Program GOTO start Jump to the Label at the start of a Subroutine CALLdelay Return at the end of a Subroutine to the next instruction RETURN Return at the end of a Subroutine with L in W RETLW OF9 Return from Interrupt Service Routine to next instruction RETFIE Control No Operation delay for 1 cycle NOP Go into Standby Mode to save power SLEEP Clear Watchdog Timer to prevent automatic reset CLRWDT Load Port Data Direction Register from W TRISO6 Load Option Control Register from W OPTION Notes The result of operations can generally be stored in W instead of the file register by adding W to the instruction General Purpose Register 1 address OC represents all file registers 00 4F Literal value OF9 represents all values 00 FF Bit 3 is used to represent File Register Bits 0 7 For MOVE instructions data are copied to the destination but retained in the source register F Any file register specified by number or label example is OC W Working register L Literal value follows instruction example is OF9 Use of these instructions not now recommended by manufacturer 92 Part 2 Listing 2 23 Assembler Block Disassembled 29 Assembler block outputs high speed pulse wave
292. t is small compared with the cost of the chip itself and accurate timing is often a necessity An external crystal and two capacitors are fitted to CLKIN and CLKOUT pins The crystal frequency in this mode can be from 200kHz to 4 MHz and is typically accurate to better than 50ppm parts per million or 0 005 A convenient value is 4 Mz as this is the maximum frequency possible with a standard crystal and gives an instruction execution time of 1 000 us 1 million instructions per second or 1 Mip A low speed crystal can be used to reduce power consumption which is proportional to clock speed in CMOS devices The LP low power mode supports the clock frequency range 32 200 kHz To achieve the maximum clock speed of 20 MHz a high speed HS crystal is needed with a corresponding increase in power consumption The MCU configuration fuses must be set to the required clock mode when the chip is programmed Many PIC chips now have an internal oscillator which needs no external components It is more accurate than the RC clock but less accurate than a crystal It typically runs at 8 MHz and can be calibrated in the chip configuration phase to provide a more accurate timing source Configuration Options Apart from the clock options several other hardware options must be selected Watchdog Timer When enabled the watchdog timer WDT automatically resets the processor after a given period default 18 ms This allows for example an applicatio
293. t it is More expensive as it contains its own microcontroller LCD Connections The parallel LCD is operated by specific combinations of inputs that enable the segments as required Figure 4 7 The segments are designated A to G for each seven segment www newnespress com C Mechatronics Applications 147 a b A RC RH DH S9 PH i 7 7 7 F B G mVA7 EF Q lt He MK Q E l C ERELT CaMV E m OID i PIN1 PIN14 c d LCD1 PIN COM1 COM2 COM3 COM4 1 COMI COM z COMI 2 loomne e e COM1 3 COM2 3 z COM3 COM2 7 COM3 4 TERAS COMA 5 R BATT MINU A COMS 5 COM 6 DH RH 4B C DP3 SEG1 6 RC BATT AC 7 3A 3F 3E 3D SEG2 DH RH B C 4DP 8 3B 3G 3C DP2 SEG3 s 3A 3F 3E 3D 3 ae oe 5E ae SEG11 g 2B 3G 3C 3DP T ik iE iE ID SEG6 10 2A 2F 2E 2D 12 1B 1G 1C SEG21 qq 28 2G 2C 2DP 13 Si S2 m M SEG22 yzl AIRED 14 A V K S3 SEG23 13 BGC SEG16 ag S1 S2 mM SEGO A V K omega Figure 4 7 a LCD Segment Connections courtesy of Varitronix Ltd b Segment Labels c MCU to LCD Connection d LCD Connection Map digit with digits numbered 1 to 4 f
294. t widely used high level language for embedded systems and can be applied by all embedded engineers from beginner to expert The overall structure of the embedded firmware is determined by the complexity and to some extent the hardware features of the host MCU A simple program can use polled 200 Part 5 T O in assembler program If the chip has an interrupt structure that allows task priority and timing to be adequately managed then interrupts can be used in assembler or C The RTOS approach may well be the best solution for more advanced applications this is the next stage in microcontroller system design to which I hope the reader will be able to progress because of the system design concepts outlined in this book There is never a perfect solution to the embedded design challenge but we can try for the best one that lies within our own limits of experience and enjoy the challenge it presents Assessment 5 5 points each unless otherwise stated total 100 1 2 10 Explain why hysteresis is useful in processing switched inputs Write two C statements that select analog input AN1 and read it and explain briefly why the variable comes first in the read statement but is given as the function argument in the select statement Draw a block diagram of a simple temperature control system consisting of a temperature sensor heater fan start and stop buttons and status indicators for running and temperature OK
295. t_D 100 amp n delay_us time incrementing and decrementing count The sine output is the most interesting as it is calculated using the sine function from the math h library These values are assigned to the amp n array for output after being calculated since to calculate each and output it on the fly would be too slow 132 Part 3 Figure 3 13 Sine Wave DAC Output The waveform is selected at the start of the program by polling the selection switch bank If the waveform selection is changed the loop must be restarted using the push button On the other hand the frequency may be modified while the output is running The main consideration here is the timing of the output waveform each step must take the same time The minimum step time is also important as this determines the highest frequency Therefore input polling is avoided Instead the Port B change interrupt is used to detect the push buttons and the period modification and waveform control operations are placed in the interrupt routine void change Here the delay between each output step is incremented or decremented or the loop stopped and restarted The sine waveform obtained is illustrated in Figure 3 13 Assessment 3 5 points each total 100 1 Write a C statement that sets up the PIC ADC so that only RAO is used as an analog input Deduce the resolution per bit for a 10 bit conversion assuming a 5V supply 2 Ifa single 4 096V reference
296. target PIC is selected from the component library and placed on the schematic The application file OUTNUM COF previously created by the compiler is attached to it Figure 2 1 and the schematic saved in the project folder When the simulation is run the state of the outputs is indicated by red and blue indicators Although not absolutely necessary for program testing in simulation mode a set of LEDs with their load resistors are attached to Port D since these are required in the actual hardware to display the outputs Figure 2 2 No other circuit components or connections are required at this stage since the simulation runs correctly without a clock circuit In the real hardware the clock circuit must be added and MCLR input tied to Vaa 5 V Here the clock frequency is set in the MCU properties dialog when the program is attached To take advantage of the full debugging facilities of MPLAB Proteus VSM can be run from within MPLAB by installing it in the debug tool menu For this a plug in needs to be downloaded from www labcenter co uk When selected the simulator runs in a VSM viewer window Figure 2 3 38 Part 2 U1 BH OSC1 CLKIN RBO INT ss MCLR VeP THV RB2 35 2 RB3 PGM 37 3 RAO ANO RB4 38 77 RA1 AN1 RB5 39 5 RA2 AN2VREF RB6 PGC 40 RAS ANS VREF RB7 PGD
297. te r resene Wied Saeed ed Ghee ate tad Sua PLE ae ae ee ESL start 0 if hunthous 0 putc hunthous 0x30 start 1 72 Part 2 if tenthous 0 start 1 putc tenthous 0x30 start 1 if thous 0 start 1 putc thous 0x30 start 1 if hunds 0 start 1 putc hunds 0x30 start 1 if tens 0 start 1 putc tens 0x30 start 1 if ones 0 start 1 putc ones 0x30 start 1 while akey 0xFF scankey PROCEDURE Derive input digits KREKEKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK void makenum keynum akey 0x30 numofdigs if numofdigs 3 hunsdig tensdig tensdig onesdig onesdig keynum if numofdigs 2 tensdig onesdig onesdig keynum if numofdigs 1 onesdig keynum PROCEDURE Scans keypad attached to Port D xKKKKKK KKK KKK KK void scankey akey 0 while akey 0 output_b 255 output_low PIN_B1 if input PIN_D1 akey 0x37 delay_ms 50 while input PIN_D1 if input PIN_D2 akey 0x38 delay_ms 50 while input PIN_D2 f input PIN_D3 akey 0x39 delay_ms 50 while input PIN_D3 if input PIN_D4 akey 0x2F delay_ms 50 while input PIN_D4 H output_b 255 output_low PIN_B2 f input PIN_D1 akey 0x34 delay_ms 50 while input PIN_D1 if input PIN_D2 akey 0x35 delay_ms 50 while input PIN_
298. temp tens ones setup_lcd LCD_MUX14 0 setup_adc ADC_CLOCK_INTERNAL setup_adc_ports sANO set_adc_channel 0 while 1 intemp read_adc temp intemp 0 488 50 distemp temp tens temp 10 ones distemp 10 tens 1led_symbol DigMap ones DIG1 lced_symbol DigMap tens DIG2 MCU header file Select 10 bit ADC UCD segment map file Start main block Input temp from ADC result Decimal result of scaling Display temp and BCD digits Initialize 14 pin LCD Select internal ADC clock Configure for ANO input Select ANO Main loop always Read analog input Convert to degC Truncate to integer Calculate BCD ones digit Display low digit Display high digit 166 Part 4 The program needs to convert the input to degrees C by multiplying the input bit count by the temperature resolution 0 488 C per bit Since the temperature range effectively starts at 0 C 500 mV we must subtract this offset from the calculated temperature For example at room temperature of 20 C the sensor output is 500 20 X 10 700 mV This converts to a value of 700 4 88 143 nearest integer We check that we see the correct display 143 X 0 488 50 19 8 C Due to rounding down in the program this displays as 19 C and changes to 20 C only when this input has been exceeded so the display shows the correct temperature accurate to 1 C and O C A corr
299. terfacing PIC Microcontrollers by the author and the MCU data books When programming in C only a limited knowledge of timer operation is necessary as the C functions generally take care of the details A D Converter Certain PIC pins can be set up as inputs to an analog to digital converter ADC The 877 has eight analog inputs which are connected to Port A and Port E When used in this mode they are referred to as ADO AD7 The necessary control registers are initialized in CCS C using a set of functions that allow the ADC operating mode and inputs to be selected An additional device directive at the top of the program sets the ADC resolution An analog voltage presented at the input is then converted to binary and the value assigned to an integer variable when the function to read the ADC is invoked The default input range is set by the supply nominally 0 5 V If a battery supply is used which drops over time or additional accuracy is needed a separate reference voltage can be fed in at AN2 V ef and optionally AN3 V er If only Vefis used the lower limit remains OV while the upper is set by the reference voltage This is typically supplied using a zener diode and voltage divider The 2 56 V derived from a 2V7 zener gives a conversion factor of 10mV per bit for an 8 bit conversion For a 10 bit input a reference of 4 096 V might be convenient giving a resolution of 4mV per bit The essentials of ADC operation are i
300. terrupt The ISR includes code to save and restore the MCU registers so that the main task can be resumed unaffected by the interrupt Only local variables should be used in the ISR to protect the integrity of the rest of the program C Peripheral Interfaces 107 U1 Ci amHz 1 A is OSC1 CLKIN RBO INT 3 oer 77 OSC2 CLKOUT RB1 35 R1 X15 MCLR Vpp THV RB2 3g 10k C2 2 RB3 PGM 37 3 RAO ANO RB4 33 15pF z RA1 AN1 RB5 39 5 RAZ AN2 VREF RB6 PGC 3o RA3 AN3 VREF RB7 PGD RA4 TOCKI_ dis RAS AN4 SS RCO T1OSO T1CKI PX B RC1 T10SI CCP2 5 Q g RE0 AN5 RD RC2 CCP1 L Jo RE1 AN6 WR RC3 SCK SCL 53 RE2 AN7 CS RC4 SDI SDA 53 RC5 SDO 55 RC6 TX CK 5 gt RC7 RX DT gt U2 Pi RDo PSPo 12 1 20 9 20 2 19 8 RD1 PSP1 213 18 7 RD2 PSP2 5 oe RD3 PSP3 5E e RD4 PSP4 C 23 6 15 4 RD5 PSP5 29 7 14 3 RD6 PSP6 S5 os RD7 PSP7 S E PIC16F877 10 t 1 l 220R Figure 3 3 External Interrupt Test Hardware Interrupt Statements The program statements associated with interrupt operation are as follows int_ext This directive tells the compiler that the code immediately following is the service routine for this particular interrupt The routine is the form in a standard function with a function name appropriate to t
301. the animated schematic allows the application to be comprehensively debugged before downloading to hardware This not only saves time for the professional engineer but provides an excellent learning tool for the student or hobbyist Preface xv Links Resources and Acknowledgments Microchip Technology Inc www microchip com Microchip Technology Inc is a manufacturer of PIC microcontrollers and associated products I gratefully acknowledge the support and assistance of Microchip Inc in the development of this book and the use of the company trademarks and intellectual property Special thanks are due to John Roberts of Microchip UK for his assistance and advice The company Web site contains details of all Microchip hardware software and development systems MPLAB IDE integrated development system must be downloaded and installed to develop new applications using the tools described in this book The data sheet for the PIC 16F877A microcontroller should also be downloaded as a reference source PIC PICmicro MPLAB MPASM PICkit dsPIC and PICDEM are trademarks of Microchip Technology Inc Labcenter Electronics www labcenter co uk Labcenter Electronics is the developer of Proteus VSM virtual system modeling the most advanced cosimulation system for embedded applications I gratefully acknowledge the assistance of the Labcenter team especially John Jameson in the development of this series of books A student evaluation vers
302. tialization Control Loop Figure B 1 Real Time Application Flowchart 210 Appendix B The initialization phase typically contains statements that include the MCU specific header and library files specific to the target device The main program is contained in a function main Variables and data structures defined at this point are global in scope recognized and unique throughout the whole program The endless loop can be started with while 1 or for both of which mean to run an endless loop unconditionally The main loop contains various conditional sequences and loops comprising data operations and function calls These functions may be built into the compiler included as additional libraries with the use directive or written by the user They process input or stored data and return results to be used by later functions for example as system output A general outline of a C program is shown in Listing B 1 Listing B 1 C Program General Outline Header comment block Include resource files Other preprocessor commands Function blocks Function name plus received parameters Local variable amp data structure declarations Unconditional sequences Conditional sequences Loop sequences Function calls Return to calling block with results Main block Variable declarations Data structure definitions Loop Unconditional Sequences Conditional Sequences Loop Sequences Function Calls Endlessly
303. ts_of star are provided These are illustrated in Figure 2 13 a screenshot of demo program POINTS C An 8 bit integer labeled num1 is declared and initialized to the value 123 Ox7B Pointer point1 is then assigned the address of num1 File RAM address 0x21 and num2 is assigned the contents of the address pointed to by point1 0x7B These values can be seen in the watch window and file register window The pointer contents_of operator can be used for accessing a sequence of data words in memory by incrementing decrementing or modifying the pointer variable The address_of operator can be used to obtain the address of the first item in the array www newnespress com C Programming Essentials 77 include 16F877A h main intg month enum none jan feb mar apr may jun enum jul 7 aug sep oct nov dec month mar while 1 17 18 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 F gt Figure 2 14 Enumeration MPLAB Screenshot These operators are useful for accessing data arrays and structures Structures are sets of data that contain different variable types mixed together but as they are used more extensively in data processing applications than real time applications they will not be covered here Enumeration Individual variables can be assigned an initial value when declared If we wish to declare a
304. ture controller 166 T O allocation 168 implementation 168 71 specification 166 7 Pick Devices button 205 PICkit2 exe file 28 POINTS C 76 Polled I O 189 90 Power up timer PuT 10 printf 75 114 Processor controls 253 Program analysis 38 40 Program blocks 239 Program compilation 87 8 Program Configuration Word 221 Program creation 36 Program debugging 221 4 Program directives 78 Program execution 3 5 Program simulation screenshot 223 PIC16F84 2 PIC16F877A 3 PICCLite 232 PICDEM analog sensors 162 Program Target Device 145 Program testing 37 8 39 Programming instruction set for 90 1 93 4 Project files 25 6 PROJNAME C 23 24 PROJNAME HEX 23 Proteus VSM 182 203 205 system testing errors 224 6 program attaching 221 program debugging 221 4 Pulse Width Modulation PWM mode 14 109 11 Punctuation syntax 239 putc 13 function 114 putc code 66 R RAM file registers 6 7 read_ADC function 100 Real time application flowchart 209 Real time counter clock RTCC see TimerO Real time operating system RTOS 18 192 4 Register OC 1219 93 Register manipulation 248 Relational operators 240 Release From Reset buttons 30 Rev counter 154 6 RISC reduced instruction set computer processor 4 ROM read only memory 1 2 RS232 20 peripheral simulation 115 serial data 64 65 serial port 246 functions 114 rtos_disable task1 194 rtos_enable task1 194 rtos_run statement 193 rtos_yield function 194
305. ture mode 111 13 CCP_1 112 CCS C 16F877 header file 11 analog input functions 103 compiler 35 interrupt functions 104 program function reference 243 analog inputs 245 block rotate 249 character test 252 C serial port 247 integers 251 interrupts 254 LCD control 248 math functions 249 50 memory allocation 255 memory read and write 254 parallel slave port 248 port input and output 244 processor controls 253 register manipulation 248 RS232 serial port 246 search and sort 253 special setup 255 SPI serial port 247 timers 245 trigonometric functions 251 type conversions 252 programming syntax 239 arithmetic and logic operators 241 compiler directives 239 formatting codes 241 T O functions 240 program blocks 239 punctuation syntax 239 relational operators 240 variable types 240 software design BARI list file 215 19 BARI source code 211 12 PIC registers 212 15 source code components 48 CCS timer function 109 Character test 252 Character variable 52 53 Clock options 9 Code protection CP 10 Communication links comparison of 123 5 Comparator 15 16 Compare mode 111 Compiler directives 239 Component button 205 Conditional operations 54 5 Conventions block diagram of 180 Counter timer operation 108 9 CR mode 9 D DC motor connections 142 Debugging 145 6 and testing application program 180 2 Decision making 42 43 delay_ms 44 Digital controller elements of 2 Digital input and output I O 12 13 Digital
306. tures However a compiler for any given microcontroller uses its own variations for processor specific operations particularly input and output processes These are fundamental to MCU programs and so will be introduced from the start Simple Program Microcontroller programs contain three main features e Sequences of instructions e Conditional repetition of sequences e Selection of alternative sequences The following basic programs show how these processes are implemented in CCS C The program in Listing 2 1 is a minimal program that simply sets the bits of an 8 bit port in the 16F877 to any required combination 36 Part 2 Listing 2 1 A Program to Output a Binary Code OUTNUM C Outputs an 8 bit code at Port D in the 16F877 MCU include 16F877A h MCU header file void main Main block start output_D 255 Switch on outputs The essential source code components can be identified The include statement tells the compiler to incorporate the header file for a particular MCU It provides information about the chip hardware features that the compiler needs to tailor the program The keywords void main indicate the start of the main program block and the associated braces curly brackets enclose the program statements This program only contains one statement the function call output_D nnn that sends a binary code to Port D Program Creation The development process was introduced in Part 1 a
307. tures to consider are e The number of I O pins e The interface types e The program memory capacity e The RAM capacity e The operating speed e The power consumption We assume that adequate development system support and driver libraries are available A logical approach to design is to select a chip that has spare capacity in relation to the draft specification The application can be prototyped in simulation mode without penalty using an overspecified device When the I O memory and peripheral requirements finally are established a chip can be selected for hardware implementation that meets the specification at minimum cost The anticipated scale of production is also a factor The cost of each individual unit produced becomes more critical as the scale of production increases On the other hand the firmware can be reproduced at effectively no cost unless variants are required If we assume a fixed cost a for design development hardware and software and each board costs b to produce the cost per unit is given by y alx b where x is the number of units produced The fixed costs are divided by the number of boards produced So if the development costs are say 1000 units of currency a 1000 and the production cost 100 per board b 100 a curve showing the cost per board as the volume of production is increased is obtained as seen in Figure 5 8 We can see that the cost per board is initially high falling away and lev
308. ucting PIC applications Identify typical memory interfacing and sensor chips that use these interfaces and summarize the range of devices available for each interface PIC Microcontroller Systems 33 Assignment 1 3 Download and install MPLAB development system from www microchip com and the demo C complier for the PIC16F877 from www ccsinfo com Create the project OUTBYTE as described in Section 1 5 Enter the source code and save in the project folder Copy the header file into the same folder Compile the program and view the files created in the folder Check that the hex 1st and cof files have been created Test the program in simulation mode arrange the MPLAB windows as seen in Figure 1 6 and check that Port C is loaded with the output byte FFh Study the assembler version of the program note the number of instructions required to implement the C output statement Reset and step through the program noting the two phases initialization and loop Change the output number in the source code from 255 to 8549 recompile and run What is the Port D output now in binary and hex C Programming Essentials 2 1 PIC16 C Getting Started e Simple program and test circuit e Variables looping and decisions e SIREN program Programming PIC microcontrollers in C is introduced here using the simplest possible programs assuming that the reader has no previous experience of the language The CCS compiler uses ANSI standard syntax and struc
309. uit the application In the code shown Listings 5 2 and 5 3 the upper switching level is 20 steps above the lower 184 Part 5 Listing 5 2 Temperature Control Program Outline TEMCON Initialize MCU 16F877A ADC 8 bits Inputs RAO RA1 RS232 Output RDO Loop Delay 500ms for display Read Set Pot 0 255 Read Temp 0 255 Scale Temp for display Display Temp on LCD line 1 If Temp below lower limit Switch ON Heater Switch OFF Fan If Heater is ON Display on LCD line 2 If Temp above upper limit Switch OFF Heater Switch ON Fan If Fan is ON Display on LCD line 2 Always In a real system the interfacing needs to be further developed The temperature sensor is likely to need an amplifier perhaps with voltage level shifting The heater and fan need a relay or contactor to operate the final load with the relay requiring a transistor interface or current driver Details of interface design can be found in Interfacing PIC Microcontrollers by the author 5 3 PIC16 C Data Logger System e BASE board hardware e Application design e Program outline Since this book is concerned mainly with software development off the shelf hardware such as the PICDEM mechatronics board featured in Part 4 is very useful This is PIC16 C Applications and Systems 185 Listing 5 3 Temperature Controller Source Code TEMCON C MPB 27 3 07 Temperature controller demo Target simulation system TEMCON DSN RHE K
310. ull version of ISIS is guaranteed to allow complete control of the simulation Therefore different versions of the mechatronics board schematic configured for testing particular applications are provided on the support Web site Assessment 4 5 points each total 100 1 Sketch a full bridge driver circuit using PFETs and NFETs connected to a motor indicating the current flow for forward motion and the logic state of the FET inputs 2 Calculate the speed of the stepper motor on the mechatronics board in rev min if it is driven at a rate of six steps per second 3 Derive a formula for the output of the temperature sensor on the mechatronics board in the form V f t 4 Suggest three disadvantages of using the 3 5 digit parallel LCD compared with the serial alphanumeric display described in Part 2 5 Write a statement to display the number 8 on digit 1 on the mechatronics board LCD and explain the meaning of each element of the statement 6 Describe briefly the hardware used to control the speed of a DC motor connected to a microcontroller 7 Outline how the position of the stepper motor on the mechatronics board is controlled and the connections required 176 Part 4 10 11 12 13 14 15 16 17 18 19 20 Outline a method for controlling the speed of the DC motor in the mechatronics board using Timer in the MCU to measure the sensor pulse period Calculate the delay required
311. un alongside MPLAB so that the full set of ISIS schematic edit tools and component models are available VSM still accesses the same COF file so both software and hardware changes can be tested More details on interactive debugging are given in Appendices A B and C 5 2 PIC16 C Temperature Controller e Basic system e Software design e Implementation In this section the software design principles just outlined are applied to a typical application a temperature control system The schematic of the demo hardware is shown in Figure 5 2 The TEMP pot represents a temperature sensor that outputs a voltage of 0 5 V If a scaling of 100mV C is assumed the range is O 50 C with 2 5 V representing 25 C System Operation The sensor is connected to AN1 the ADC channel 1 A SET pot provides the reference temperature for the system If the measured temperature is below the set level a heater PIC16 C Applications and Systems 183 TEMPERATURE CONTROLLER temcon dsn A SET TEMP BH OSC1 CLKIN RBO INT 32 44 OSC2 CLKOUT RB1 S MCLP Vpp THV RB2 2 5 RB3 PGM pS K 3 RAO ANO RB4 S 7 E z RA1 AN1 RB5 35 oa 5 RA2 AN2 VREF RB6 PGC 7 3 6V RAS ANS VREF RB7 PGD 22 6 Ras TOCKI 10k A Z RA5 AN4 55 RCO TIOSo T1cKI X RCITIOSI CCP2 E 3 REo AN5 RD RC2 CCP1 mre A Fo REVANG WR RC3 SCK SCL 18 10 _ RE2 AN7 CS RC4 SDI
312. up to 9 BCD1 0 Reset ones BCD2 Increment tens if BCD2 10 up to 90 BCD2 0 Reset tens BCD3 Increment hundreds if BCD3 10 up to 900 BCD3 0 All reset to zero DISPLAY BCD DIGITS 1lcd_symbol DigMap BCD1 DIG1 Display Digit 1 1lced_symbol DigMap BCD2 DIG2 Display Digit 2 1lcd_symbol DigMap BCD3 DIG3 Display Digit 3 Loop always SATII IITTTTTT ITT TATA TTT ATT TTT TAA ATT TIAA TTT TAT TTT TT 1 SEND 154 Part 4 Run Switch PIC 16F917 LCD Drive 1 Current Source Opto Sensor Drive 2 Current Sink Figure 4 8 Block Diagram of Motor Test System Listing 4 5 Motor Test Program MOTOR1 C MPB 17 4 07 Control motor from switch Connect SW2 RA4 include 16F917 h void main while 1 if input PIN_A4 output_D 0x90 else output_D 0x00 PICDEM board test program RD7 P1 Test switch Switch on motor Switch off motor RD4 N2 Rev Counter The system is now developed to measure the number of revolutions completed during a short run The motor is still attached to Drivel and Drive2 outputs but in addition the output from the opto sensor OPTO which produces two pulses per rev is connected to the Timer1 input on the MCU RC5 T1CLKI The motor is switched on by pressing SW2 and the number of revs is displayed when it is released The maximum rev cou
313. upt Figure 1 9 shows a program sequence where a timer is run to generate an output pulse interval An interrupt routine ISR has been written and assigned to the timer interrupt The timer is set up during program initialization and started by preloading or clearing it The main program and timer count then proceed concurrently until a time out occurs and the interrupt is generated The main program is suspended and the ISR executed When finished the main program is resumed at the original point If the ISR contains a statement to toggle an output bit a square wave could be obtained with a period of twice the timer delay When interrupts are used in assembly language programs it is easier to predict the effect as the programmer has more direct control over the exact sequence of the ISR 18 Part 1 Program Execution 1 Lp 2 Start Counter Run Statement Counter until Program Execution Overflow 3 Time out Interrupt 4 4 Jump to ISR 7 Continue p 5 Time out Process Interrupt Service 6 Routine Return from Interrupt Figure 1 9 Timer Interrupt Process A C program is generated automatically by the compiler so the precise timing that results from an interrupt is less obvious For this reason the use of a real time operating system RTOS is sometimes preferred in the C environment especially when programs become more complex In fact C was originally developed for p
314. upts 104 C interrupts 104 5 example 106 7 interrupt statements 107 8 operating systems 189 interrupts 190 1 PC operating system 191 2 polled I O 189 90 RTOS 192 4 parallel and serial interfaces 121 communication links comparison of 123 5 parallel slave port 121 3 124 program analysis 38 40 program basics 40 blank program 47 48 decision making 42 43 FOR loop 45 loop control 42 44 looping 41 2 SIREN program 45 7 variables 40 1 program creation 36 program testing 37 8 39 sequence control 56 break continue and goto 57 9 if else and switch case 59 60 61 while loops 56 7 serial bus 116 18 119 simple program 35 6 system design 195 hardware design 197 9 hardware selection 195 6 microcontrollers 196 7 198 software design 199 200 temperature controller 182 software design and implementation 183 4 185 system operation 182 3 UART serial link 113 15 light sensor 162 3 164 temperature measurement 163 6 board simulation 171 172 circuit description 173 5 DC motor test programs 152 154 control 152 154 Rev counter 154 6 hardware 137 8 139 140 141 142 143 liquid crystal display 146 BCD count program 152 153 LCD connections 146 9 LCD test program 149 52 mechatronics board overview 137 138 debugging 145 6 motor drives 138 139 142 143 PICDEM hardware 137 8 139 140 141 142 143 test program 143 5 stepper motor control 156 construction 157 8 direction control 158 62 stepper motor test 158 159 160 tempera
315. ut change 106 Part 3 Listing 3 3 External Interrupt Test Program Source Code INTEXT C MPB 10 4 07 Demo external interrupt RBO low interrupts foreground output count include 16F877A h use delay clock 4000000 int_ext Interrupt name void isrext Interrupt service routine output_D 255 ISR action delay_ms 1000 void main LEEA KK kk k kkk kkk kk kkk kk k k k k k k ERE kk k k k k k k k k k k k k int x enable_interrupts int_ext Enable named interrupt enable_interrupts global Enable all interrupts ext_int_edge H_TO_L Interrupt signal polarity while 1 Foreground loop output_D x x delay_ms 100 Interrupt Example Program INTEXT C Listing 3 3 demonstrates the basic interrupt setup An output count represents the primary task This is interrupted by the switch input at RBO going low forcing the execution of the interrupt service routine which causes all the output LEDs to come on for 1 second The original task is then automatically resumed at the point where it was interrupted It is designed to run on the hardware shown in schematic Figure 3 3 When the RBO interrupt is detected during the main loop the context current register contents is saved before the ISR executed If the program execution is studied carefully it can be seen that the original count prior to the interrupt is restored to the port output after the in
316. veform with a 50 duty cycle should be observed on the display Now rewrite the program to produce the same output using compare mode in Timer1 The timer needs to run for 2ms for each half cycle assuming a 4 MHz MCU clock and a 1 MHz timer clock a compare value of 2000 is needed Assignment 3 3 Download the project DACWAVE and test it for correct operation Measure the minimum and maximum frequencies available Modify the arbitrary waveform data to produce a step waveform that has amplitude 0 for five steps of the output 5 for the next five steps 10 for the next five steps and so on until the amplitude reaches 90 over the last five steps then reduces to 0 again It should then produce the same over the negative half cycle of the waveform before repeating C Mechatronics Applications 4 1 PICDEM Mechatronics Board Overview e Mechatronics board hardware e Mechatronics board connections e Mechatronics board motor drives The PICDEM mechatronics demonstration board Figure 4 1 supplied by Microchip Inc is a very useful target system for C control applications A user manual which can be downloaded from www microchip com contains the schematics and general guidance on using the board It can be programmed using the ICD2 In Circuit Debugger module which allows a final stage of fault finding when testing an application in the target hardware Alternatively the low cost PicKit2 programmer can be used Since our applications here have b
317. void low_interrupt void _asm GOTO timer_isr _endasm pragma code pragma interruptlow timer_isr void timer_isr void static unsigned char led_display 0 INTCONbits TMROIF 0 s_count s_count NUMBER_OF_LEDS 1 led_display 1 lt lt s_count 1 PORTB led_display void main void TRISB 0 PORTB 0 OpenTimer0 TIMER_INT_ON amp TO_SOURCE_INT amp TO_16BIT INTCONbits GIE 1 J while 1 e Support for 24 bit and 32 bit IEEE floating point and 32 bit long data types included e Mixed C and assembler programming e Unlimited number of source files 232 Appendix D e Listings showing generated assembler e Compatible integrates into the MPLAB IDE MPLAB ICD and most third party development tools e Runs on multiple platforms Windows Linux UNIX Mac OS X Solaris Optimization involves reducing the final code size by removing redundant code and modifying the assembler version to reduce the number of instructions to the minimum achievable The most obvious disadvantage of this compiler is that only the standard library functions for data conversion memory management mathematical operations and basic I O are provided It is assumed that the user will develop the peripheral drivers as required to suit the particular range of applications and hardware to be supported or that the peripheral control registers will be accessed directly On the
318. voltage is connected to V and 10 bit conversion completed write a C statement a to declare suitable variables and b to convert the input value to the actual voltage for display 10 11 12 13 14 C Peripheral Interfaces 133 List the statements required to set up an ADC interrupt and outline the related ISR initialization if it is called isrADC Explain the advantages of using an interrupt to read the data from an analog input conversion compared with simply checking it on a regular basis polling within the program loop A 16 bit timer is preloaded with a value of 15 536 The MCU clock runs at 8 MHz with a prescaler set to divide by 16 Calculate the timer output interval obtained Explain briefly the difference between the Capture and Compare modes of operation Draw a labeled diagram to show a PWM waveform indicating how the overall period and duty cycle are set by the arguments of functions setup_ timer_2 a b c and set_PWMx_duty d The MCU instruction clock period is T Calculate modified parameters for the setup functions in program PWM that produce an output at 1 kHz with a duty cycle of 10 0 1 ms pulse The instruction clock is 1 MHz Explain why the UART is a suitable interface for transmission of characters to a serial LCD display especially if the LCD is separated from the MCU board Explain the effect of the statements printf d incode and putc incode on an LCD display connect
319. witch Conditional branching operations are a basic feature of any program These must be properly organized so that the program structure is maintained and confusion avoided The program then is easy to understand and more readily modified and upgraded While Loops The basic while condition provides a logical test at the start of a loop and the statement block is executed only if the condition is true It may however be desirable that the loop block be executed at least once particularly if the test condition is affected within the loop This option is provided by the do while condition syntax The difference between these alternatives is illustrated in Figure 2 7 The WHILE test occurs before the block and the DO WHILE after The program DOWHILE shown in Listing 2 9 includes the same block of statements contained within both types of loop The WHILE block is not executed because the loop control variable has been set to 0 and is never modified By contrast count is incremented within the DO WHILE loop before being tested and the loop therefore is executed C Programming Essentials 57 Listing 2 9 DOWHILE C Contains Both Types of While Loop DOWHILE C Comparison of WHILE and DO WHILE loops include 16F877A H main int outbytel 0 int outbyte2 0 int count This loop is not executed count 0 while count 0 output_C outbytel outbytel t count
320. x4 D s6F8770 n wor void main a E output D 255 inciude 16F877A h void maini CLEE Ox4 BCE 0x3 0x7 MOVLW Oxit amur 0x3 F F A BSE 0x3 Ox E Special Function Registers BSE Oxit 0 WREG BSF Oxlf Ox2 BCE Oxi 0x3 0 0000000 MOVLW Ox 0 0000000 MOVE Oxi 4 0000100 amen 28 0011100 0000000 Oi ope 0 0000000 MOVE Oxe 0 0000000 SLEEP 0 0000000 255 1111111 0 0000000 0 0000000 0 0000000 Figure 1 16 Screenshot of MPLAB Project outbyte err The error file provides debugging messages which are displayed in the Output Build window after compilation outbyte sym The symbol map shows the register locations in which the program variables are stored outbyte mcp This is the MPLAB project information file outbyte mcw This is the MPLAB workspace information file outbyte pjt This is the CCS compiler project information file 1 6 PIC16 Program and Debug e Programming the chip e In circuit debugging e Design package www newnespress com PIC Microcontroller Systems 27 Figure 1 17 PICkit2 Demo System Hardware reproduced by permission of Microchip Inc Once the compiler has produced the hex file it can be downloaded to the target application board However it is generally preferable to test it first by software simulation This means running the program in a virtual MCU to test its logical function This can be done within MPLAB tabular output or using a third party
321. y chip hardware address is 000 The system reads a test code set manually on Port B inputs which is copied to the serial memory Pull ups must be fitted to the serial clock and data lines and a virtual PC analyzer is also attached to the bus The test program writes the test byte 3F in the 120 Part 3 D 12CMEM MPLAB IDE v7 52 Fie Edt View Project Debugger Programmer Tools Configure Window Help OSH sh SAV Reese VSSD iH cura E Ce Output O X C M2CMEM C Buld Version Consol Find in Fies Proteus VSM void main int sendbyte lowadd lowadd 0 port_b_pullups 1 sendbyte input_B while 1 i2e_start i2c_write 0xA0 i2c_write 0x00 i2c_write lowadd i2c_write sendbyte i2e_stop delay_ms 5 lowadd Z I E SADA COA AFA BFAP 2 152 sS ADA OO A SOA BPAP 2 157 eS ADA OO ASLABFAP IF IF IF SFI 3F OF OF nps 3F 3F SFF OF OF OF A 3F 3F 3F 3F 3F 3F 3F 3F 3F 36 3F 3F 3F 3F 3F 3F KERRE A TRUA A T IF IF 3F IF IF IF 3F 3F 3F IF IF IF IF IF DF OF 2 169 s SADA OOASIAJI AP 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 2 175 s S AO A 00 A S4A3PAP 0040 3F 3F 3F 3F 3F 3F 3F IF 3F 3F 3F 3F 3F IF IF IF 0050 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 0060 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F 3F g Figure 3 9 I C Test System example shown to the address lowadd which increments from 0 after each write The i2c_start function initiates the data transfer sequence
322. y into qsort Sort array al ofn ascending order al n w sort1 elements of width w using function sortit Table F 17 Processor Controls Requires Chip Header File Only e g 16F877A H Function Description Example Comment GET Gets information chip Peripheral hardware ENVIRONMENT about the MCU getenv device memory configuration etc GOTO ADDRESS Jump to program memory location goto_ address Ox1FFO Jump in ROM use with caution LABEL ADDRESS Check address of labloc Labels should be used program label label_address only in exceptional cases start RESET CPU Restarts the reset_cpu No return program from 0 RESTART CAUSE Returns cause of last message Messages defined in reset restart_cause MCU header file RESTART Clear watchdog restart_wdt Periodical operation to WATCHDOG timer prevent MCU watchdog reset SETUP Select internal clock setup_ MCUs with internal OSCILLATOR mode oscillator clock SLEEP Stops program and sleep Wake up on specific waits for reset events 254 Appendix F Table F 18 Interrupts Requires Chip Header File e g 16F877A H amp INT_XXXX Function Description Example Comment INTERRUPT Disables peripheral disable_interrupts Interrupt labels DISABLE interru
323. y particular circuit must be as closely matched as possible to the actual needs of the application Some of the main features to consider are e Number of inputs and outputs e Program memory size e Data RAM size e Nonvolatile data memory e Maximum clock speed e Range of interfaces e Development system support e Cost and availability The PIC16F877A is useful as a reference device because it has a minimal instruction set but a full range of peripheral features The general approach to microcontroller application design followed here is to develop a design using a chip that has spare capacity then later select a related device that has the set of features most closely matching the application requirements If necessary we can drop down to a lower range PIC10 12 series or if it becomes clear that more power is needed we can move up to a higher specification chip PIC18 24 series This is possible as all devices have the same core architecture and compatible instructions sets The most significant variation among PIC chips is the instruction size which can be 12 14 or 16 bits The A suffix indicates that the chip has a maximum clock speed of 20 MHz the main upgrade from the original 16F877 device These chips can otherwise be regarded as identical the suffix being optional for most purposes The 16F877A pin out is seen in Figure 1 2 and the internal architecture in Figure 1 3 The latter is a somewhat simplified version of
324. yte to slave port output_high PIN_E1 Reset write enable C Peripheral Interfaces 123 Listing 3 11 PSP Slave Test Program PSPSLAVE C Test system slave controller program design file PSP DSN U2 include 16F877A h void main LEE EKEk kk kkk kkk kkk kkk kkk kk kk kk k k k k k kk k kk k k int recbyte setup_psp PSP_ENABLED Enable PSP slave port while 1 if psp_input_full If data have been received recbyte input_D Copy in test data output_C recbyte Display data on bar graph chip select on Port E and the data are latched in when E1 wR not write is pulsed low by the master In simulation mode the write pulse frequency was measured at 40 kHz MCU clock 4MHz The slave program Listing 3 11 monitors the receive flag associated with the port and picks up the data when the port indicates that data have been loaded into the PSP data register The data then are transferred to Port C for display on the bar graph A parallel external bus can thus be created that connects microcontrollers extra memory and other 8 bit devices to form a system similar to a conventional microprocessor system On the PSP bus the master must select the peripheral device to be accessed using the chip select mechanism If necessary an address decoding system can be added to expand the hardware without using extra master pins For example a 3 bit decoder
325. ytes 16Fh 80 Bytes 1EFh accesses 170h accesses 1FOh 7Oh 7Fh 47Fh 70h 7Fh _ 4Feh Bank 2 Bank 3 Figure B 2 PIC 16F877 File Registers by permission of Microchip Technology Inc 213 214 Appendix B Address Name Bit7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bito Value on Details POR BOR on page Bank 0 00h INDF Addressing this location uses contents of FSR to address data memory not a physical register 0000 0000 31 150 Oth TMRO TimerO Module Register xxxx xxxx 55 150 o2h PCL Program Counter PC Least Significant Byte 0000 0000 30 150 03h STATUS IRP RP1 RPO TO PD Z DC Cc 0001 1xxx 22 150 04h FSR Indirect Data memory Address Pointer xxxx xxxx 31 150 05h PORTA PORTA Data Latch when written PORTA pins when read 0x 0000 43 150 06h PORTB PORTB Data Latch when written PORTB pins when read XXXX XXXX 45 150 07h PORTC PORTC Data Latch when written PORTC pins when read xxxx xxxx 47 150 osh PORTD PORTD Data Latch when written PORTD pins when read xxxx xxxx 48 150 ogh PORTE RE2 RE1 REO xxx 49 150 oAn 3 PCLATH Write Buffer for the upper 5 bits of the Program Counter 0 0000 30 150 oBh INTCON GIE PEIE TMROIE INTE RBIE TMROIF INTF RBIF 0000 000x 24 150 OCh PIRI PSPIF A

Programming 8-bit PIC Microcontrollers in C 2008

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