----- Original Message -----
From: Jess Hancock <jhancock@CWV.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, February 28, 2001 12:26 AM
Subject: How2 erase/modify/reprogram 12c671


> Hi
>
> This is my first PIC project - the code was written by someone else and
> I'm just trying to duplicate it.

<snip>

> Therefore, I need to modify the hex or asm code to include a routine to
> program the correct calibration value into the OSCCAL register.  The
initial
> code for the program begins at 0000h and is listed below - I hope its
> readable.  (The MPLAB disassembler prefixes memory locations with "ad".
>
>             ;
>              ORG 0000h
>             ;
>              MOVLW  0x00   ;original code
>              MOVWF  PCLATH
>              GOTO  ad007F
>             ;
>
> The program code ends with the following:
>
> ad00CE       CLRF   0x24
>              BSF   STATUS,RP0
>              BCF   GPIO,3               ; ??? RAM Page TRISIO,3
>              BCF   STATUS,RP0
>              BCF   GPIO,3               ; ??? RAM Page TRISIO,3
>             ;
> ad00D3 GOTO  ad0094
>             ;
>              SLEEP    ; (This is apparently never called)
>             ;
>             ORG   03FFh
>             ;
>              RETLW  0x88               ; (This is not the correct value
for
> my  671)
>
> Will the following patch work or is there a better way?
> Thanks in advance.  Jess
>
> 0000  GOTO 00D6
>   .
>   .
>   .
> 00D6  CLRF  GPIO   ;not sure if this is required
>           CALL  0X3FF  ; RETLW with OSCCAL at 0x03FF
>           BSF  STATUS,RP0 ;BANK 1
>           MOVWF OSCCAL
>           BCF  STATUS,RP0 ;BANK 0
> ;
>           MOVLW 0x00   ;relocated original code from 0000h starts here
>           MOVWF PCLATH
>           GOTO  007Fh   ;Go continue with remainder of program
> ;
>           ORG  03FFh
>           RETLW 0x40   ;The correct calibration value

Jess, you have the right idea, but you should be sure that PCLATH is clear
before
you do anything else.

I'd use:

    org    0x0
    movlw    0
    movwf    PCLATH
    goto        0xD6

    org    0xD6
    call    0X3FF        ; get osccal value
    bsf     STATUS,RP0
    movwf OSCCAL
    bcf    STATUS,RP0

    movlw    0
    goto        0x7F

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

    ORG    0x02
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
>

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.