You either need to use the interupt to determine when the write is complete, or add a delay to ensure the write completes.  Refer to the data sheet where it details exactly how the write sequence occurs.  


--- On Mon, 11/3/08, Hasan Khan <hasan@khansden.com> wrote:

> From: Hasan Khan <hasan@khansden.com>
> Subject: [PIC] EEPROM won't change
> To: "PIC List" <piclist@mit.edu>
> Date: Monday, November 3, 2008, 6:35 AM
> Hi,
> I have a project where I need to write some constant values
> into eeprom of a 16f84a.  I am writing the code in mplab and
> testing it on its simulator.  This code won't work
> because simulator shows no change in eeprom values or the
> registers EECON1 and EECON2.  It does show EEDATA and EEADR
> changin.  Here is the simplified code.  Thanks for any help.
> 
> #include p16f84a.inc
> 
> list p=16f84a
> 
>   org        0x00
> 
>   ;initialize EEPROM
>   banksel    EEDATA
>   movlw        0x34
>   movwf        EEDATA
>   movlw        0x01
>   movwf        EEADR
> 
>   bsf        STATUS, RP0        ; BANK 1
>   bcf        INTCON, GIE
> 
>   bsf         EECON1, WREN     ; Enable Write
>   movlw     0x55
>   movwf     EECON2             ; Write 55h
>   movlw     0xAA
>   movwf     EECON2             ; Write AAh
>   bsf         EECON1,WR         ;  Set WR bit
> 
>   bsf        INTCON, GIE
>   bcf        STATUS,RP0        ; BANK 0
> 
>   end
> 
> 
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