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TB025
ACCESSING MEMORY
The read and write operations are controlled by a set of Special Function Registers (SFRs). There are six SFRs required to access the FLASH program memory: * * * * * * EECON1 EECON2 EEDATA EEDATH EEADR EEADRH
Downloading HEX Files to PIC16F87X PICmicro(R) Microcontrollers
Rodger Richey Microchip Technology Inc.
INTRODUCTION
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The release of the PIC16F87X devices introduces the first mid-range family of devices from Microchip Technology that has the capability to read and write to internal program memory. This family has FLASH-based program memory, SRAM data memory and EEPROM data memory. The FLASH program memory allows for a truly reprogrammable system. Table 1 shows the features of the PIC16F87X family of devices.
The registers EEADRH:EEADR holds the 12-bit address required to access a location in the 8K words of program memory. The registers EEDATH:EEDATA are used to hold the data values. When reading program memory, the EEPGD bit (EECON1<7>) must be set to indicate to the microcontroller that the operation is going to be on program memory. If the bit is cleared, the operation will be performed on data memory at the address pointed to by EEADR. The EEDATA register will hold the data. The EECON1 register also has bits for write enable and to initiate the read or write operation. There is also a bit to indicate a write error has occurred, possibly due to a reset condition happening while a write operation is in progress. Figure 1 shows the register map for EECON1. The EECON2 register is not a physical register. Reading it will result in all '0's. This register is used exclusively in the EEPROM and FLASH write sequences. Listing 1 shows the code snippet to initiate a write operation on the PIC16F87X devices.
TABLE 1
PIC16F87X FAMILY FEATURES
Key Features PIC16F873 DC - 20 MHz POR, BOR 4K 192 128 13 Ports A,B,C 3 2 MSSP, USART -- 5 input channels PIC16F874 DC - 20 MHz POR, BOR 4K 192 128 14 Ports A,B,C,D,E 3 2 MSSP, USART PSP 8 input channels PIC16F876 DC - 20 MHz POR, BOR 8K 368 256 13 Ports A,B,C 3 2 MSSP, USART -- 5 input channels PIC16F877 DC - 20 MHz POR, BOR 8K 368 256 14 Ports A,B,C,D,E 3 2 MSSP, USART PSP 8 input channels
Operating Frequency Resets Flash Prog Memory (14-bit words) Data Memory (bytes) EEPROM Data Memory Interrupts I/O Ports Timers Capture/Compare/PWM modules Serial Communications Parallel Communications 10-bit Analog-to-Digital Module
(c) 1998 Microchip Technology Inc.
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TB025
FIGURE 1:
R/W-x U-0 EEPGD -- bit7
EECON1 REGISTER
U-0 -- U-0 -- R/W-x R/W-0 WRERR WREN R/S-0 WR R/S-0 RD bit0
R= Readable bit W= Writable bit S= Settable bit U= Unimplemented bit, read as `0' - n= Value at POR reset
bit 7:
EEPGD: Program / Data EEPROM Select bit 1 = Accesses Program memory 0 = Accesses data memory Note: This bit cannot be changed while a write operation is in progress. Unimplemented: Read as '0' WRERR: EEPROM Error Flag bit 1 = A write operation is prematurely terminated (any MCLR reset or any WDT reset during normal operation) 0 = The write operation completed WREN: EEPROM Write Enable bit 1 = Allows write cycles 0 = Inhibits write to the EEPROM WR: Write Control bit 1 = initiates a write cycle. The bit is cleared by hardware once write is complete. The WR bit can only be set (not cleared) in software. 0 = Write cycle to the EEPROM is complete RD: Read Control bit 1 = Initiates an EEPROM read (read takes one cycle) RD is cleared in hardware. The RD bit can only be set (not cleared) in software. 0 = Does not initiate an EEPROM read on the line. Divide this number by two to get the number of words per line. AAAA - is a four digit hexadecimal address representing the starting address of the data record. Format is high byte first followed by low byte. The address is doubled because this format only supports 8-bits (to find the real PICmicro address, simply divide the value AAAA by 2). TT - is a two digit record type that will be '00' for data records, '01' for end of file records and '04' for extended address record (INHX32 only). HHHH - is a four digit hexadecimal data word. Format is low byte followed by high byte. There will be BB/2 data words following TT. CC - is a two digit hexadecimal checksum that is the two's complement of the sum of all the preceding bytes in the line record.
bit www..com6:4: bit 3:
bit 2:
bit 1:
bit 0:
HEX FILE FORMAT
The data to be programmed into program memory will be read into the microcontroller using one of its standard interface modules: SPI, I2CTM, USART, or PSP. Probably the simplest format to send the data to the microcontroller is in the standard HEX format used by the Microchip development tools. The formats supported are the Intel HEX Format (INHX8M), Intel Split HEX Format (INHX8S), and the Intel HEX 32 Format (INHX32). The most commonly used formats are the INHX8M and INHX32 and therefore are the only formats discussed in this document. Please refer to Appendix A in the MPASM User's Guide (DS33014) for more information about HEX file formats. The difference between INHX8M and INHX32 is that INHX32 supports 32-bit addresses using a linear address record. The basic format of the hex file is the same between both formats as shown below: :BBAAAATTHHHH...HHHHCC Each data record begins with a 9 character prefix and always ends with a 2 character checksum. All records begin with a ':' regardless of the format. The individual elements are described below. * BB - is a two digit hexadecimal byte count representing the number of data bytes that will appear
DS91025A-page 2
*
*
*
*
Since the PIC16F87X devices only have a maximum of 8K words, the linear address record '04' is ignored by the routine. The HEX file is composed of ASCII characters 0 thorough 9 and A to F and the end of each line has a carriage return and linefeed. The downloader code in the PICmicro microcontrollers must convert the ASCII characters to binary numbers to be used for programming.
(c) 1998 Microchip Technology Inc.
TB025
PICmicro Code
The sample downloader code does not specifically use one of the interface modules on the PIC16F87X device. Instead, a routine called GetByte retrieves a single character from the HEX file over the desired interface. It is up to the engineer to write this routine around the desired interface. Another routine GetHEX8 calls GetByte twice to form a two digit hexadecimal number. One issue that arises is how many times to reprogram a location that does not program correctly. The sample code provided simply exits the downloader routine and stores a value of 0xFF in the WREG if a program memory location does not properly program on the first attempt. The engineer may optionally add code to loop several times if this event occurs. www..com Still another issue that is not specifically addressed in the sample code is to prevent the downloader from overwriting its own program memory address locations. The designer must add an address check to prevent this situation from happening. Finally, the designer must account for situations where the download of new code into the microcontroller is interrupted by an external event such as power failure or reset. The system must be able to recover from such an event. This is not a trivial task, is very system dependent, and is therefore left up to the designer to provide the safeguards and recovery mechanisms. Another error that could happen is a line checksum error. If the calculated line checksum does not match the line checksum from the HEX file, a value of 1 is returned in WREG. The part of the routine that calls the downloader should check for the errors 0xFF (could not program a memory location) and 1. If program memory is programmed correctly and no errors have been encountered, the downloader routine returns a 0 in WREG to indicate success to the calling routine. Figure 2 shows the flowchart for the downloader routines. Listing 2 shows the complete listing for the downloader code. The routine ASCII2HEX converts the input character to a binary number. The routine does not provide any out of range error checking for incoming characters. Since the only valid characters in a HEX file are the colon (:), the numbers 0 through 9 and the letters A through F, the routine can be highly optimized. It first subtracts 48 from the character value. For the ASCII numbers 0 through 9, this results in a value from 0 to 9. If the character is A through F, the result is a number greater than 15. The routine checks to see if the upper nibble of the result is 0. If not 0, then the original value was A through F and the routine now subtracts an additional 43 from the character resulting in the binary values 10 through 15. The colon is not accounted for in this routine because the main part of the downloader code uses it as a line sync.
LISTING 1:
bsfSTATUS,RP1 bcfSTATUS,RP0 movfAddrH,W movwfEEADRH movfAddrL,W movwfEEADR bsfSTATUS,RP0 bsfEECON1,EEPGD bsfEECON1,RD bcfSTATUS,RP0 nop movfEEDATA,W ... movfEEDATH,W ...
FLASH WRITE SEQUENCE
; Bank2 ; Load address into ; EEADRH:EEADR
; ; ; ;
Bank3 Set for Prog Mem read operation Bank2 ; Data is read ; user can now ; access memory
(c) 1998 Microchip Technology Inc.
DS91025A-page 3
TB025
LISTING 2: HEX DOWNLOAD CODE WRITTEN FOR MPASM
list p=16f877 #include "c:\progra~1\mplab\p16f877.inc"
DownloadCode banksel DCStart call movlw subwf btfss goto call movwf movwf bcf rrf call movwf addwf call movwf addwf call movwf addwf DataRec movf btfss goto DRLoop movf btfsc goto call movwf addwf call movwf addwf WriteDataSequence banksel movf movwf movf movwf movf movwf movf movwf banksel bsf bsf bcf movlw movwf movlw movwf bsf nop
;Uses USART to receive data from PC RCREG GetByte ':' RCREG,W STATUS,Z DCStart GetHex8 ByteCount LineChecksum STATUS,C ByteCount,F GetHex8 AddrH LineChecksum,F GetHex8 AddrL LineChecksum,F GetHex8 RecType LineChecksum,F
;Wait for colon
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;Read byte count ;Store in register ;Store in line checksum ;Divide byte counter by 2 to get words ;Read high byte of 16-bit address ;Add high byte to line checksum ;Read low byte of 16-bit address ;Add low byte to line checksum ;Read record type ;Add to line checksum ;Data reception ;Check for data record (0h) ;Otherwise check for EOF ;Check for bytecount = 0 ;If zero, goto checksum validation ;Read lower byte of data (2 characters) ;Add received data to checksum ;Read upper byte of data (2 characters) ;Add received data to checksum
RecType,F STATUS,Z EndOfFileRec ByteCount,F STATUS,Z DRCkChecksum GetHex8 HexDataL LineChecksum,F GetHex8 HexDataH LineChecksum,F
;Write sequence to internal prog. mem FLASH EEADRH AddrH,W EEADRH AddrL,W EEADR HexDataH,W EEDATH HexDataL,W EEDATA EECON1 EECON1,EEPGD EECON1,WREN INTCON,GIE 0x55 EECON2 0xaa EECON2 EECON1,WR ;Write address to EEADRH:EEADR registers
;Write data to EEDATH:EEDATA registers
;Write sequence ;Set EEPGD to indicate program memory ;Enable writes to memory ;Make sure interrupts are disabled ;Required write sequence
;Start internal write cycle
DS91025A-page 4
(c) 1998 Microchip Technology Inc.
TB025
nop bcf banksel bsf bsf bcf nop movf subwf btfss retlw movf subwf btfss retlw www..com incf btfsc incf decf goto EECON1,WREN EECON1 EECON1,EEPGD EECON1,RD STATUS,RP0 EEDATH,W HexDataH,W STATUS,Z 0xff EEDATA,W HexDataL,W STATUS,Z 0xff AddrL,F STATUS,Z AddrH,F ByteCount,F DRLoop ;Disable writes ;Read sequence ;Set EEPGD to indicate program memory ;Enable reads from memory
;Compare memory value to HexDataH:HexDataL
;If upper byte not equal, return FFh ; to indicate programming failure
;If lower byte not equal, return FFh ; to indicate programming failure ;Increment address for next iteration
;Decrement byte count ;Go back to check for ByteCount = 0 ;Checksum verification ;Read in checksum ;Add to calculated checksum ;Result should be 0 ; If not return 1 to indicate checksum fail ;Do it again ;End of File record (01h) ;If EOF record, decrement should = 0 ;Not valid record type, wait for next : ;Read in checksum ;Add to calculated checksum ;Result should be 0 ; If not return 1 to indicate checksum fail ;Otherwise return 0 to indicate success
DRCkChecksum call addwf btfss retlw goto EndOfFileRec decf btfss goto call addwf btfss retlw retlw
GetHex8 LineChecksum,W STATUS,Z 1 DCStart
RecType,W STATUS,Z DCStart GetHex8 LineChecksum,W STATUS,Z 1 0
GetByte ; Insert your code here to retrieve a byte of data from ; the desired interface. In this case it is the USART on F877. ;clear CTS ; banksel PIR1 ;GH4Waitbtfss PIR1,RCIF ; goto GH4Wait ;set CTS nop banksel RCREG movf RCREG,W return GetHex8 call call movwf swapf call call iorwf movf return GetByte ASCII2Hex Temp Temp,F GetByte ASCII2Hex Temp,F Temp,W ;This function uses the USART ;Read a character from the USART ;Convert the character to binary ;Store result in high nibble
;Read a character from the USART ;Convert the character to binary ;Store result in low nibble ;Move result into WREG
(c) 1998 Microchip Technology Inc.
DS91025A-page 5
TB025
ASCII2Hex movwf movlw subwf movlw andwf btfsc goto movlw subwf ASCIIOut movf return end www..com Temp1 '0' Temp1,F 0xf0 Temp1,W STATUS,Z ASCIIOut 'A'-'0'-0x0a Temp1,F Temp1,W ;Convert value to binary ;Subtract ASCII 0 from number
;If number is 0-9 result, upper nibble ; should be zero
;Otherwise, number is A - F, so ;subtract off additional amount ;Value should be 0 - 15
DS91025A-page 6
(c) 1998 Microchip Technology Inc.
TB025
FIGURE 2: FLOWCHART
Download Code
2
No RecType = 1?
3
Move AddrH:AddrL into EEADRH:EEADR
1
Get a single byte GetByte Yes Read Checksum and add to LineChecksum No Character = :?
1
Move HexDataH:HexDataL into EEDATH:EEDATA
Set EEPGD and WREN bits Result = 0? Yes No Write 55h to EECON2
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Yes Read ByteCount and store in LineChecksum
Return with W = 0 Divide by 2 to get # of words
Return with W = 1 Write AAh to EECON2
Set WR bit Read AddrH and add to LineChecksum Wait for EE Write complete Read AddrL and add to LineChecksum Set RD bit Read RecType and add to LineChecksum Return with W = FFh No Record type = 0? RecType = 0? Yes
No EEDATH = HexDataH? Yes No Return with W = FFh Yes EEDATA = HexDataL? Yes Continue with program
2
ByteCount = 0? No Read DataH and add to LineChecksum
Read Checksum and add to LineChecksum
Read DataL and add to LineChecksum
Result = 0? No
Yes
1
3
Return with W = 1 Decrement ByteCount
(c) 1998 Microchip Technology Inc.
DS91025A-page 7
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WORLDWIDE SALES AND SERVICE
AMERICAS
Corporate Office
Microchip Technology Inc. 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 602-786-7200 Fax: 602-786-7277 Technical Support: 602 786-7627 www..com Web: http://www.microchip.com
AMERICAS (continued)
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ASIA/PACIFIC (continued)
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Microchip received ISO 9001 Quality System certification for its worldwide headquarters, design, and wafer fabrication facilities in January, 1997. Our field-programmable PICmicro(R) 8-bit MCUs, Serial EEPROMs, related specialty memory products and development systems conform to the stringent quality standards of the International Standard Organization (ISO).
All rights reserved. (c) 1998 Microchip Technology Incorporated. Printed in the USA. 10/98
Printed on recycled paper.
Information contained in this publication regarding device applications and the like is intended for suggestion only and may be superseded by updates. No representation or warranty is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Use of Microchip's products as critical components in life support systems is not authorized except with express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property rights. The Microchip logo and name are registered trademarks of Microchip Technology Inc. in the U.S.A. and other countries. All rights reserved. All other trademarks mentioned herein are the property of their respective companies.
DS91025A-page 8
(c) 1998 Microchip Technology Inc.

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