Hi,
here is the appropriate code fragment for your convenience.
BTW the 16-bit CRCUpd below is written by me, too.

Regards,
Imre

On Thu, 11 Feb 1999, Wing Kent Kwan wrote:

> Hi.
>     have someone have CRC32 PIC source file?
> THANK
>
> > >
> > > ; What you need is to define the polynomial. E. g. for the CCITT one:
> > >
> > > poly0 equ 0x21
> > > poly1 equ 0x10
> > >
> > > ; Do not forget to initialize <crcval> = <crch:crcl> before the 1st call
> > > ; e. g. with 0xFF or with zeroes, as the particular CRC algorithm
> > > ; requires.
> > >
> > > ;This subroutine calculates a 16-bit CRC
> > > ;--------
> > > ; CrcUpd: update <crcval> using <W>
> > > ;
> > > ;
> > >         CBLOCK     crcblk
> > >            crch
> > >            crcl
> > >            saved
> > >            oldcch
> > >            i
> > >         ENDC
> > > CrcUpd  movwf   saved           ; j = W
> > >         movlw   d'8'            ; W = 8
> > >         movwf   i               ; i = W
> > > _loop   movfw   crch
> > >         movwf   oldcch          ; temporary save
> > >         clrc                    ; clear carry for rlf
> > >         rlf     crcl            ; crc << 1
> > >         rlf     crch
> > >         movfw   saved           ; the char read
> > >         xorwf   oldcch,F        ; test with old high
> > >         btfss   oldcch,7        ; if bit set, apply mask
> > >         b       _notset         ; otherwise skip
> > >         movlw   poly0
> > >         xorwf   crcl,F
> > >         movlw   poly1
> > >         xorwf   crch,F
> > > _notset clrc                    ; for rlf
> > >         rlf     saved,F         ; next bit of saved
> > >         decfsz  i,F
> > >         b       _loop
> > >         return
> > > ;
> > > ; End CrcUpd
> > >
> > > More at:
> > > http://www.piclist.com/faq
> > >
> > > James Newton
> > > mailto:jamesnewton@geocities.com
> > > 1-619-652-0593 phone
> > > http://www.piclist.com

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