Hi,

I try use this subroutine to write to data EEPROM.
In my main routine, I use this code:

FCALL   EEPROM_init

The function EEPROM_init didn't work as my LCD always show the message
indicate that failure in writing to EEPROM.

I am using F877 chip, and W0~W7 stay at 0x70, what should I call this area
of RAM? A 'shared bank RAM' ?


Subrutine listing:

EEPROM_init
;***************************************************************************
******
; Initialize EEPROM from 0x00 ~ 0xFF to value 0x00
;
; BF
;***************************************************************************
******
        clrf    W7      ; 256 bytes of Data EEPROM to be
                        ; initialize. Address to
                        ; access EEPROM.
NextAddress
        movf    W7, w
        movwf   W0      ; Address.
        movlw   0xFF    ; Data.

        call    EEPROM_write

        movwf   W6      ; For checking write result.
        movf    W6, f
        skpz
        goto    WriteNG ; NG
        incf    W7, f   ; OK, increase address.
        skpz            ; Are ROM finish?
        goto    NextAddress     ; No
        retlw   0x00    ; Yes
WriteNG FCALL   LCD_clear
        FCALL   LCD_home
        DispMsg EEPROM_WriteNG
        movlw   0xFF
        FCALL   X_DELAY500
        FCALL   LCD_clear
        retlw   0xFF

EEPROM_write
;***************************************************************************
*
; Input: Address to be write in W0
;        Data to be write in W
;
; Output: If write-verify OK, w = 0
;                         NG  W = 0xFF
;***************************************************************************
**
        BANK3
        btfsc   EECON1, WR      ; Make sure no writing
        goto    $-1     ; operation in progress.
        BANK2
        movwf   EEDATA  ; Data to be write. ??
        movf    W0, w   ;
        movwf   EEADR   ; Address to be written.
        BANK3
        bcf     EECON1, EEPGD   ; Point to data memory.
        bsf     EECON1, WREN    ; Enable WRITE.
        bcf     INTCON, GIE     ; Disable ISR.
        btfsc   INTCON, GIE     ; Confirm?
        goto    $-2
        movlw   0x55    ; 0x55 must be written to EECON2
        movwf   EECON2  ; to start write sequence
        movlw   0xAA    ; Next, write 0xAA to EECON2
        movwf   EECON2
        bsf     EECON1, WR      ; Set WR bit begin write
        bcf     EECON1, WREN    ; Disable WRITE.
EEPROM_verify   bsf     EECON1, RD
        btfsc   EECON1, RD
        goto    $-1
        BANK2
        ; Is the data in W0 same as EEDATA?
        movf    W0, w
        subwf   EEDATA, w

        BANK0
        bsf     INTCON, GIE     ; Enable interrupt.
        btfss   STATUS, Z       ; Is 0?
        retlw   0xFF    ; No, return 0xFF
        retlw   0x00    ; Yes, return 0x00


I have no clue for the result I get here. I have check through the contents
of EEPROM and there  are not updated to 0xFF.

May someone help me on this?

Thanks & regards.

WH Tan

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