Hi

This is my first PIC project - the code was written by someone else and
I'm just trying to duplicate it.  The hex code POLAR.HEX is posted on
a web page at http://www.qsl.net/ke4hor/polar.htm .  It is for a really neat
radio direction finding (RDF) system which can also be used to display the
directional pattern of a beam antenna.

I obtained the un-commented assembler code via MPLAB from the posted hex
code.  The 12c671 I m using has the wrong oscillator calibration value at
03ff.  The original program makes no provision for re-programming  the value
of OSCCAL when programming an erased  671.

The program outputs the A/D values to another program, POLAR.EXE, via RS232
(I think).  Viewing the A/D output on a scope shows the values changing as
the dc inputs are varied so it appears that the  671 program is working.
However, no communication between the two programs results, not even any
garbage characters.  I wonder if the timing is thrown off enough so that the
receiving program does not recognize the characters.  I have tried several
baud rates.

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

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