On Wed, 13 Aug 1997 10:22:19 PDT Shane Buckham <goweed@HOTMAIL.COM>
writes:
>I
>
>Here is a portion of the code in two parts macro and eewrite
>subroutine.
>
>
>{macro write_ee}
>
>WRITE_EE        MACRO   ADR, DAT
>
>                        movlw           ADR
>                        movwf           EEADR
>                        movf            DAT,W
>                        movwf           EEDATA
>                        call            Write_EEProm
>
>                        ENDM
>
>{Subroutine Write_EEprom}
>
>Write_EEProm:          PAGE1                    ;Macro, move to page 1
>                       bcf     EECON1-0x80,WRERR
>                       bcf     EECON1-0x80,EEIF
>                       movlw   0x55
>                       movwf   EECON2-0x80
>                       movlw   0xAA
>                       movwf   EECON2-0x80
>                       bsf     EECON1-0x80,WR
>
>Wait_EEProm:           btfss   EECON1-0x80,EEIF
>                       goto    Wait_EEProm
>                       bcf     EECON1-0x80,WREN
>                       PAGE0                    ;Macro, back to page 0
>return
>
>I would appreciate any suggestions you could offer.
>
You need to have WREN set before attempting to set WR (and before the 55,
aa stuff) in the write routine.  Hardware doesn't set or clear WREN
except to clear it on a reset.   I have had good results ignoring the
WRERR and EEIF bits and polling the WR bit.  It will stick at 1 until the
write completes.  While waiting, be sure to clear the WDT if it is set up
for a short time.  The WRERR bit is only of relevance if you want to be
able to recover from a reset while a write was in progress.

If you have an interrupt that reads the EEPROM, it must be disabled while
a write is in progress.

Once you get it working, you can save a code word everytime you reuse
WRITE_EE by moving the movwf EEDATA into the Write_EEProm subroutine.