PIC microcontroller EEPROM reading and writing examples and instructions

; PIC microcontroller EEPROM reading and writing examples and instructions
;************************************************************************
; This is a program to test the function of reading&writting for EEPROM.
; You can observe the value of register(30H--?) buy changing "VALU" and "WRC_".
; Notice that:it must be { ADDR+WRC_<=0ffh } !

;****************************************************************************
include "p16f877.inc"
ADDR EQU 20H ;Write address register
VALU EQU 21H ;Write value
REC_ EQU 22H ;Read count
WRC_ EQU 24H ;Write
countorg 0
goto main
main
bcf STATUS,RP1
bcf STATUS,RP0 ;bank0
movlw 10h
movwf ADDR ;Write EEPROM initial value
movlw 90h
movwf VALU ;Initial write value
movlw 30h
movwf FSR ;Indirect address, read value initial storage address
movlw 0Fh
movwf WRC_ ;Write times
movwf REC_
;incf REC_ ;Read times
wri_ ;Write subroutine
bsf STATUS,RP1
bsf STATUS,RP0 ;bank3
btfsc EECON1,WR
goto $-1
bcf STATUS,RP0
bcf STATUS,RP1 ;bank0
movf ADDR,W
bsf STATUS,RP1 ;bank2
movwf EEADR
bcf STATUS,RP1 ;bank0
movf VALU,W
bsf STATUS,RP1 ;bank2
movwf EEDATA
bsf STATUS,RP0 ;bank3
bcf EECON1,EEPGD ;to data memory
bsf EECON1,WREN
bcf INTCON,GIE
movlw 55h
movwf EECON2
movlw 0aah
movwf EECON2
bsf EECON1,WR
bcf STATUS,RP0
bcf STATUS,RP1 ;bank0
incf ADDR,1
decf VALU,1
decfsz WRC_ ;all write,to read_
goto wri_
read_ ;read subroutine
bcf STATUS,RP1
bcf STATUS,RP0 ;bank0
decf ADDR ;next value
bsf STATUS,RP1 ;bank2
movwf EEADR
bsf STATUS,RP0 ;bank3

EEw&r.asm program description:

1. This program is a demonstration program for reading and writing the EEPROM data area of ​​the PIC16F877 microcontroller;

2. wri_ is a data writing subroutine. This subroutine starts writing to the EEPROM data area from the address determined by the ADDR register (the example starts from 10H). Each write operation will increase the ADDR value by one. The initial value of the written data is given by the VALU register (the example value is 90H). Each write operation will decrease the VALU value by one. After writing the specified number of values ​​(given by the WRC_ register, the example value is 0FH), the writing is terminated and the program goes to read_.

3. read_ is a subroutine for reading data. This subroutine starts reading the EEPROM data area from the address determined by the current value of the ADDR register (current value = ADDR + WRC_ <= 0FFH). Each read operation will reduce the ADDR value by one. After reading the data, the program will store the data in a general register. The starting address is specified by the value of FSR (30H in the example). Each read operation will increase the value of FSR by one. After reading the specified number of values ​​(given by the register REC_, the example value is 0FH), the reading is completed and the program returns to main.