Hello Folks,
I am having some difficulty with writing to the data
eeprom in a 16F877.
I coded in some data at org 2100 and can read the data
with no problem. When I try to write to one of the
address, it destroys the existing data.
I am using code from the Microchip data for 16F87X as
follows:

write_eeprom
        ; writes data into PIC EEPROM

        bsf     STATUS, RP1
        bsf     STATUS, RP0     ; bank 3

        btfsc   EECON1, WR
        goto    $-1

        bcf     status, RP0

        ; get and write the memory address
        ;call   ser_in          ; get address
        movlw   0x03            ; hard code addr for
debug
        movwf   EEADR           ; address to register

        ; get and write the data
        ;call   ser_in          ; get data
        movlw   0x41            ; hard code data for
debug
        movwf   EEDATA          ; data into memory

        bsf     STATUS, RP0
        bcf     EECON1, EEPGD   ; point to Data memory
        bsf     EECON1, WREN    ; enable write
        bcf     INTCON, GIE     ; disables INT's

        movlw   0x55
        movwf   EECON2          ; 55h must be written
to EECON2
        movlw   0xAA            ;   to start write
sequence
        movwf   EECON2          ; write AAh

        bsf     EECON1, WR      ; set WR bit, begin
write
        bsf     INTCON, GIE     ; restore ints.
        bcf     EECON1, WREN    ; disable writes
        return

I have hard coded the address and data for debug
purposes. Running the simulator does not show any
change in the EEPROM WINDOW when this runs.
Hope someone can shed some light on this as I have
spent many days experimenting to no avail.
Regards,
Sandy Phelps


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