AT89C51 In-Circuit Programming Application Note 8
Contents
1. ATX ASX is the filename of the compiled ASPECT script to be associated with External Protocol 1 Save the changes and exit the Setup utility Creating a Hex File The hex files which are uploaded to the programmer are created with the tools in the Intel MCS 51 Software Devel opment Package for the IBM PC In the example below the 8051 assembler source file is called TEST ASM Assemble the source file TEST ASM and create the object file TEST OBJ ASM51 TEST ASM Link and locate the object file TEST OBJ and create the absolute object file TEST ABS RL51 TEST OBJ TO TEST ABS Convert the absolute object file TEST ABS to the hex file TEST HEX OH TEST ABS TO TEST HEX The resulting file TEST HEX is ready to be uploaded Note ASM51 is version 2 3 RL51 is version 3 1 OH is version 1 1 Uploading a Hex File Run Procomm Plus and use the proper dialing directory entry to dial the remote station After the connection with the remote station is established press the PgUp key and select 1 External Protocol 1 from the menu of upload protocols This will execute the ASPECT script associated with External Protocol 1 When prompted enter the name of the file to be uploaded including the extension and path if required When the upload is complete press ALT H to hang up and ALT X to exit Procomm Plus and return to DOS 5 15 AIMEL Figure 1 AT89C51 Moving Display Application Exampl2. FTP Receive Mode 5 20 AIMEL Begin QO Send NAK U A Disable Programming A Send ACK F Erase AT89C51 Enable Programming gt Od Packet Header Y Get Packet Programming Enabled Microcontroller Verify Data N Send CAN X I Vv Abort ees CO CO I I Appendix I Intel Hex File Definition Hexadecimal object file format Intel hex is produced by most 80051 assembler products Each record in the file contains the following fields lt gt lt rec length gt lt load address gt lt rec type gt lt data gt lt check sum gt The colon is the record header The record length field consists of two hex digits and rep resents the number of entries in the data field OH outputs records containing 16 or fewer data field entries The load address field consists of four hex digits and indi cates the absolute address at which the data in the data field is to be loaded The record type field consists of two hex digits which are always zero in data records The data field contains from one to 16 pairs of hex digits The last two hex digits are a checksum on the record length load address record type and data fields The sum of the binary equivalents of these fields and the checksum itself is zero Each record in the file is terminated by a carriage return and line feed A type one record marks the end of the file The re
3. packet data Successful verifi cation indicates successful programming causing the pro grammer to send ACK to the transmitter If programming fails the programmer sends CAN to signal the transmitter to abort the file transfer The simplicity of the FTP reduces the amount of AT89C51 program memory used in the programmer The send and wait nature of the FTP allows inter packet delays due to AT89C51 program and erase times to be easily absorbed Support for program verification is transparent requiring no explicit command or result codes or additional data trans fers The files which are uploaded to the programmer are cre ated with the tools in the Intel MCS 51 Software Develop ment Package for the IBM PC Included in the package are the MCS 51 Macro Assembler MCS 51 Relocator and Linker and a useful utility OH OH converts an absolute 8051 object file to an equivalent ASCII hexadecimal object file The records in the hex file produced by the OH utility serve unchanged as the packets in the FTP described above no service fields need to be added The colon which begins each record serves as the packet signature field The load address field serves as the packet sequence number A checksum is provided as the last field in each record Since seven bit ASCII coding is utilized the eighth bit of each byte is available to be used for parity checking Because the AT89C51 in the programmer does not utilize external data memory neces
4. preventing it from executing the incomplete or invalid program which it contains It is important to note that invalid packets are NEVER pro grammed into the application controller To do so would require that the program memory in the controller be com pletely erased before the error could be corrected causing the non recoverable loss of all previous program data Upon receipt of an end of file packet the programmer returns its control outputs to the inactive power on state allowing the application controller to begin execution of the new program The programmer then resumes polling for a valid packet header subject to the thirty second reset delay If a valid packet is received prior to the expiration of the thirty second delay another programming cycle begins which can only be terminated by the reception of a valid end of file packet Microcontroller memm ees CO CO I 1 If the reset delay expires prior to the reception of a valid end of file packet the modem will drop the line and the pro grammer will return to sleep waiting for the next call In this case the application controller is left in programming mode preventing it from executing its program To return the application to normal operation another call must be received and a valid program file uploaded terminated by an end of file packet Setting Up the Hardware Local Station Connect the IBM PC to the ProModem 1200 through one of the
5. AT89C51 In Circuit Programming This application note illustrates the in cir cuit programmability of the Atmel AT89C51 Flash based microcontroller Guidelines for the addition of in circuit programmability to AT89C51 applica tions are presented along with an appli cation example and the modifications to it required to support in circuit program ming A method is then shown by which the AT89C51 microcontroller in the application can be reprogrammed remotely over a commercial telephone line The circuitry described in this appli cation note supports five volt program ming only requiring the use of an AT89C51 XX 5 The standard AT89C51 requires 12 volts for programming The software for this application may be obtained by downloading from Atmel s BBS 408 436 4309 General Considerations Circuitry added to support AT89C51 in circuit programming should appear transparent to the application when pro gramming is not taking place EA VPP must be held high during pro gramming In applications which do not utilize external program memory this pin may be permanently strapped to Vcc Applications utilizing external program memory require that this pin be held low during normal operation RST must be held active during pro gramming A means must be provided for overriding the application reset cir cuit which typically asserts RST only briefly after power is applied PSEN must be held low during program ming but must n
6. RI AT89C51 vec TI En 74HCT157 N V ad 10K DL1414T R5 am 10K u5 Re 8 WW a 4 R7 AAlAlA a Bilas Holl A 10K 1 0 A11 0 5 4 P3 7 P3 6 a4 moo DL1414T P2 7 P26 Note 0 1 uF bypass caps on all ICs AIMEL su AIMEL Figure 3 AT89C51 Programmer VCC oO DATA 7 0 ca T 10 uF 4 c5 vec LJ 30 pF iz EA VPP PO O R8 y2 PO 1 8 2K XTAL1 P0 2 11 0592 MHz Bas c6 P0 4 XTAL2 PO 5 30 pF P0 6 RST PO 7 P3 0 RXD P2 0 10 K SIP P3 1 TXD P2 1 P3 2 INTO P2 2 P3 3 INT1 P2 3 P3 4 TO P2 4 P3 5 T1 P2 5 Note 0 1 uF bypass caps on all ICs P2 6 P1 0 P2 7 P1 1 P1 2 P1 3 PSEN P P1 4 ALE PROG P1 5 pe P1 6 P3 6 WR PSEN P1 7 P3 7 RD RESET AT89C51 PROG SHUTDN VCC c7 It 10 6 3 c8 a Vv 10 6 3 oO o AE cio T 10 6 3 L c9 cio IT 10 16 10 16 c2 Da TIOUT TIIN RX T2OUT T2IN DSR R1IN RIOUT R2IN R2OUT DB25 S DTE Vv MAX232 5 18 Microcontroller m Microcontroller Figure 4 FTP Transmit Mode O Get Next Record gt O Send Record Receive ACK F Receive NAK U Tx Attempts Exceeded Y N Receive N Last Record CAN AX Y lt oq End AIMEL a Figure 5
7. cord always contains the following value 00000001FF AIMEL a
8. e vec e Eci T 10 uF DL1414T rq it 30pF 31 EAIVPP Poo gt Ri m E P0 1 8 2K iiz XTAL1 P0 2 F Pos fag T 18 la rs XTAL2 P0 5 53 L 30 pF 9 PO 6 32 v RST P0 7 10 P3 0 RXD p2 0 i H P3 1 TXD P2 1 155 13 P3 2 INTO P2 2 HES 19 Ps g NTi P2 3 55 P3 4 TO P2 4 SI 1S p3 sitt p2 5 He a P2 6 1 8 11 p19 pa 28 2 ti 2 P41 3 6 3 P1 2 4 5 4 P1 3 PSEN p22 5 P1 4 ALE PROG 20 SW DIP 4 6 pis i 7 P1 6 P3 6 WR is 8 p47 P3 7 RD V AT89C51 e Note 0 1 uF bypass caps on all ICs DL1414T DL1414T 5 16 Microcontroller memm ees COC ONTO CT Figure 2 AT89C51 Moving Display Application Modified for In Circuit Programming DATA 7 0 RESET vec 21 a sl 2N2222A DL1414T c2 a2 2N2222A 2 RI or Y1 8 eek SM I T XTAL2 Nee N 30 pF p sr NH P 5 3 0 RXD x P3 1 TXD r P3 2 INTO 3 SHUTDN P3 3 INTI P3 4 TO P3 5 T1 DL1414T AO 3 4 P1 0 kd amp Al 5 7 is A 6 FSEN 8 1 8 A2 11 9 ris SEN 2 P1 4 ALE PROG Gr 2 7 10 Bis u 74HCT373 3 6 I A3 14 12 P1 6 P3 6 WR V De 4 5 a P1 7 P3 7 RD a SW DIP 4
9. e programmer verifies the connect code and begins polling for a valid packet header Incoming packets must arrive fewer than thirty seconds apart or the modem drops the line hangs up and the pro grammer returns to sleep waiting for the next call If the caller hangs up the thirty second period must expire before another call will be answered Calls incoming during the reset delay period are ignored If a valid packet header is received prior to the expiration of the reset delay period the programmer will attempt to read and validate the incoming packet At any time during packet reception an invalid character parity error or time out during character reception will cause the partial packet to be declared invalid and discarded Two packet types are defined data and end of file A data packet contains five fields in addition to the packet header one of which is a variable length data field The data field contains program data to be written into the AT89C51 con 5 14 troller in the application The load address field contains the address at which the data is to be written The end of file packet contains the same fields as the data packet except that the data field is empty This packet type has special meaning to the programmer as explained below Any packet which contains an invalid record type record length or checksum is invalid Program data accumulated during the processing of an invalid packet is discarded The prog
10. mming The Programmer The programmer Figure 3 generates the addresses data and control signals necessary to program the AT89C51 embedded in the application The programmer circuitry consists of an AT89C51 and an RS 232 level translator The controller runs at 11 0592 MHz which allows the serial port to operate at a number of standard baud rates A Maxim MAX232 line driver receiver produces RS 232 levels at the serial interface while requir ing only a five volt supply Many of the signals generated by the programmer are con nected directly without buffering to the AT89C51 in the application These signals when inactive are not three stated but are pulled high The AT89C51 has internal pull ups of approximately three Kohms on ports one two and three Because port zero does not have internal pull ups external pull ups of ten Kohms have been added to permit proper operation of program verification mode The sample application operates correctly in this environment If required for compatibility with an application programmer signals may be buffered with three state buffers similar to the 74xx125 The AT89C51 in the programmer does not utilize external program or data memory which would require sacrificing needed I O pins This requires that program code and I O buffers be kept small enough to fit in on chip memory Microcontroller memm ees COC ONTO Remote Programming Over a Commercial Telephone Line The p
11. nd programmed into the AT89C51 embedded in the application When programming is complete the appli cation is allowed to begin execution of its new program and the programmer returns to monitoring the phone line for the next call The programmer powers up with its programming control outputs inactive allowing the application to run normally After configuring the modem to answer incoming calls the programmer puts itself to sleep The programmer will not disturb the application until a new program is to be down loaded The programmer controls the modem by sending ASCII command strings over the serial interface to which the modem responds with Hayes style ASCII numeric codes The software is designed for use with Hayes compatible modems which includes the Prometheus ProModem 1200 used here The serial interface through which the programmer con nects to the modem supports two handshaking signals DTR and DSR On power up the programmer asserts DTR to which the modem responds by asserting DSR If the modem should fail to respond to any command includ ing the command to hang up the programmer deasserts DTR which forces the modem to drop the line The modem monitors the phone line while the programmer sleeps waiting for an incoming call When a call is detected the modem answers and attempts to establish communication with the caller If a connection is estab lished the modem sends a code to the programmer wak ing it up Th
12. ot be driven during nor mal operation ALE PROG is pulsed low during pro gramming but must not be driven during normal operation During programming AT89C51 I O ports are used for the application of mode select addresses and data possibly requiring that the controller be isolated from the application circuitry How this is done is application dependent and will be addressed here only in general terms Port Used for Input During programming the controller must be isolated from signals sourced by the application circuitry A buffer with three state outputs might be inserted between the application circuitry and the control ler with the buffer outputs three stated when programming is enabled Alter nately a multiplexer might be used to select between signal sources with sig nals applied to the controller by either the application circuitry or the program mer circuitry Port Used for Output No circuit changes are required if the application circuitry can tolerate the state changes which occur at the port during programming If the prior state of the application circuitry must be maintained during programming a latch might be inserted between the controller and the application circuitry The latch is enabled during programming preserving the state of the application circuitry An Application Example The AT89C51 application shown in Fig ure 1 is an implementation of a moving display This application was selec
13. rammer when inactive will nei ther drive nor excessively load the application Since the application does not use external program mem ory EA VPP on the controller is connected to Vcc This meets the requirement for programming The reset circuit has been modified by the addition of two transistors which allow RST on the controller to be forced high by the programmer PSEN and ALE PROG unused in the basic application are under the direct control of the programmer Programming requires programmer access to all of the four AT89C51 I O ports as documented in the data sheet The programmer is connected directly to those controller pins which are unused by the application while access to pins used by the application requires special treatment as explained in the following paragraphs The least significant four bits of the address generated by the programmer are multiplexed onto port one of the con troller with the data from the DIP switch Note that the four resistors added at the switch are not required in the basic application since the AT89C51 provides internal pull ups on port one During the normal operation of the application controller ports zero and two provide data and control signals respectively to the displays During programming and pro gram verification the programmer asserts control of port zero and part of port two The programmer is connected to ports zero and two without buffering since when inactive it
14. rammer sends a NAK to the transmitter to signal reception of an invalid packet and resumes polling for a valid packet header Receipt of the first valid data packet causes the program mer to interrupt the application controller The controller responds to the interrupt by abandoning execution of its usual program and displaying a message indicating that programming is taking place If this is the first valid data packet since power was applied or an end of file packet was received the programmer asserts the control signals necessary to erase the program memory in the application controller The programmer then places the controller in programming mode The first and subsequent valid data packets are dissected as they are received and the data which they contain is pro grammed into the application controller at the address indi cated in the packet load address field After programming the data is read back from the controller and verified against the received packet data Successful verification indicates that programming was successful causing the programmer to send ACK to the transmitter The program mer then resumes polling for a valid packet header subject to the thirty second reset delay If programming fails the programmer sends CAN to signal the transmitter to abort the file transfer The modem drops the line and the programmer returns to sleep waiting for the next call The application controller is left in program ming mode
15. rogrammer and display application described previ ously are connected to a phone line via a modem ata remote site Using a personal computer with amodem a user can upload a new program containing a new mes sage which is programmed into the AT89C51 embedded in the application When programming is complete the appli cation executes the new program which displays the new message Local Station The local station in the test configuration consists of an IBM PC AT class computer connected to a Hayes compatible Prometheus 1200 baud modem The modem was selected because it was inexpensive and available A faster modem may be used if desired although once the file transmission time is reduced below one minute further reductions in transmission time do not further reduce connect time charges A possible advantage to higher transmission speeds is the automatic error detection and correction available in some high speed modems Procomm Plus version 2 01 a commercial data communi cations package is used to configure the modem set up communications parameters and establish a link with the remote modem Procomm Plus includes a macro language called ASPECT which allows the user to write and compile scripts which implement custom file transfer protocols A simple ASPECT script was written to read the contents of a program file and upload it to the remote programmer The file transfer protocol FTP implemented is a simple send and wait packe
16. s presence does not affect the normal operation of the application 5 12 A transparent latch has been added between port two of the controller and the display control inputs The latch holds the display control signals inactive during programming which eliminates erratic operation of the displays due to programmer activity on ports zero and two No isolation of the display data inputs is required since data applied to the inputs is ignored when the control signals are inactive The AT89C51 reset circuit input multiplexer and output latch are controlled by a single signal generated by the pro grammer During programming reset is asserted the multi plexer switches inputs and the latch freezes the display control lines To ensure that the display control lines are in a known state before they are latched an AT89C51 external interrupt is used to allow the programmer to signal the application before asserting reset The application firmware responds to the interrupt by displaying a message and deactivating the display control lines After programming when reset is deasserted the controller ports are high as the latch becomes transparent Since the display control inputs are inactive high the display contents are not disturbed until the new program writes the display Although not essential to this application it might be imper ative in some applications that the state of the peripheral circuitry not be disturbed during progra
17. sary packet buffering must be done using internal RAM Limited memory precludes the use of conventional FTPs which utilize packets of 128 bytes and larger The hex packet format used in this appli cation limits packet data fields to 16 or fewer entries requir ing little memory for buffering The ready availability of a utility for creating the packetized program file combined with small packet size and ade quate error checking makes the hex packet format a near ideal solution for this application A disadvantage is the use of ASCII which requires each program data byte to be expressed as two hex characters This demands that nearly twice as many bytes be transferred as might other wise be required This is not a severe limitation however since typical file transfer times are less than one minute Overall the simplicity of the custom FTP hex packet format implementation outweighs the drawbacks Remote Station The remote station in the test configuration consists of the display application and programmer circuits described pre viously connected to a Hayes compatible Prometheus 5 13 AIMEL 1200 baud modem During normal operation the applica tion executes its internal program while the modem and programmer monitor the phone line for incoming calls After a call has been detected and a connection estab lished the programmer forces the application to suspend execution of its program The new program is then down loaded a
18. system COM ports Connect the modem to an analog telephone line and set the modem switches as indicated below Switch settings ON ON OFF ON OFF ON OFF OFF OFF OFF OAN OAR ON oO Remote Station Connect the display application programmer to the second ProModem 1200 through the programmer serial port Con nect tne modem to an analog telephone line and set the modem switches as indicated below Turn the modem on and apply power to the display applica tion programmer The application will begin executing its program if it contains one The programmer will initialize the modem as shown by the activity on the modem status indicators Switch settings ON ON ON OFF ON ON ON OFF OFF OFF oonoD Va A ON oO AIMEL Installing and Configuring Procomm Plus Version 2 01 Install Procomm Plus as instructed in the User Manual When prompted to specify the modem in use select Prometheus ProModem 1200 from the list Run Procomm Plus and create a dialing directory entry for the remote station The baud rate must be set to 1200 par ity to EVEN number of data bits to 7 number of stop bits to 1 plex to HALF Enter the Setup utility ALT S Select PROTOCOL OPTIONS then EXTERNAL PROTOCOL OPTIONS from the menus and modify the entry for EXTERNAL PROTO COL 1 as indicated below EXTERNAL PROTOCOL 1 A NAME lt any name gt B TYPE ASPECT C UPLOAD COMMAND ATX ASX Note
19. t oriented protocol The transmit and receive modes of the FTP are illustrated by the flowcharts in figures 4 and 5 respectively The transmitter sends each packet without flow control and waits for a response The programmer the receiver reads and dissects the packet while calculating a checksum If the calculated checksum is valid the programmer acknowledges the packet by send ing an ACK If the checksum is in error the programmer negatively acknowledges the packet by sending a NAK Upon receipt of an ACK the transmitter sends the next packet If the transmitter receives a NAK it resends the same packet Transmission proceeds in this manner until the entire file has been transferred The programmer might respond to a packet by sending a CAN which indicates that a non recoverable error has occurred and that the transmitter should immediately abort the file transfer If the programmer fails to respond to a packet within a limited period of time the transmitter will resend the same packet The transmitter will continue to resend the same packet until a valid response is received or until the allowed number of attempts is exceeded at which time the file transfer is aborted AIMEL After each packet is received and validated by the pro grammer the data contained in the packet is programmed into the AT89C51 controller in the application After pro gramming the data is read back from the controller and verified against the received
20. ted for its simplicity and ability to show graphi cally the results of in circuit reprogram ming The text to be displayed is pro grammed into the controller as part of its firmware and cannot be changed with out reprogramming the device AIMEL 8 Bit Microcontroller with Flash Application Note 0287D B 9 97 5 11 AIMEL The displayed text is presented in one of two modes selected by the four position DIP switch In the first mode one character at a time enters the display from the right and moves quickly to the left through each element of the display to its final position in the assembled message In the second mode the message moves through the display from right to left with the display acting as a window onto the message This mode is familiar as the method often used in displays of stock prices The output consists of four DL1414T four digit 17 seg ment alphanumeric displays with integral decoders and drivers This yields 16 total display elements each capable of displaying digits 0 9 the upper case alphabet and some punctuation characters The displayable character codes are ASCII 20H 5FH A power on reset circuit and a 6 MHz crystal oscillator complete the application Neither external program memory nor external data memory is used Modifications to the Application to Support In Circuit Programming Figure 2 shows the application modified for in circuit programming It is assumed that the prog
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