Hi,
here is an implementation for your convenience. Remarks:
- poly is a CRC polynomial, e.g. 0x1021
- crcval is <crcl:crch>

Maybe the implementation is not optimal, but I use it extensively, w/o any
problems.

Imre


On Mon, 30 Nov 1998, Ohtsji, Randie wrote:

> Hello,
>
> I have seen a few implementations of generating CRC values but I wanted to
> know if there is some known values which can be used to check if the CRC
> algorithm is correct, as all the routines I have come across generate
> different CRC values.
>
> For example, if the CRC is to be generated on a single byte, in this case
> the value 'FF', what should the CRC value be?
>
> Also, if the CRC is to be generated on a string of bytes, such as, 'A0',
> 'FF', '05', '02', '00', 'DE' etc. what should the end CRC value be?
>
> I am looking for a list inputs and outputs from a known good CRC-16
> generator.
>
> I think the poly for CRC-16 is X16, X15, X2, and X0.
>
> I am trying to do this on a 16C63.
>
> Any help would be appreciated.
>
> Randie
> randie.ohtsji@glenayre.com
>
>

Content-Type: TEXT/PLAIN; charset=US-ASCII; name="crc16.inc"
Content-ID: <Pine.LNX.3.96.981201081946.219B@prof.pmmf.hu>
Content-Description:

;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