On Tue, 25 Feb 1997, Riccardo Bianchi wrote:

> I'm looking for a way for implementing CRC calculation on C84.
> I'm crazy? May be!

I do not think that you are crazy at all. Bellow you will find a routine
that I wrote in X86 assembler that does One Pass per Byte and accumulate
the CRC16 of a message (routine CRC16) and a routine that checks a buffer
to see if a recieved CRC16 is valid (routine ck_crc16). My only request is
that after you modify it to PIC assembler you share it with the list.

Chaipi

PS. Do not ask me how it works, it DOES.

;*****************************************************************************
;*                                                                           *
;* ROUTINE      : ck_crc16                                                   *
;*                                                                           *
;* PROGRAMMER   : CHAIPI WIJNBERGEN                                          *
;* LAST REVISED : 26.01.1986                                                 *
;*                                                                           *
;* INPUT        : data in a buffer pointed by a pointer in stack             *
;* OUTPUT       : crc16 calculated & returned AX                             *
;*                                                                           *
;* DESTROYS     : none                                                       *
;*                                                                           *
;* CALLED BY    : c program                                                  *
;* CALLING      : crc16                                                      *
;*                                                                           *
;*****************************************************************************

_ck_crc16 proc   far

        save    bp
        mov     bp,sp
        save    ax,bx,cx,si,es   ; macro push registers

        mov     si,ss:[bp+6]                    ;get pointer offset from stack
        mov     ax,ss:[bp+8]                    ;get pointer segment
        mov     es,ax                           ;use es

        sub     ax,ax
        sub     bx,bx
        sub     cx,cx

        mov     cl,es:byte ptr [si+len]         ;length of data filed
        add     cx,head_crc                     ;add header+type+len
char1:
        cmp     cx,0                            ;end of buffer count?
        jz      buf_end1                        ;yes get out

        mov     ah,es:byte ptr [si]             ;get data byte from buf
        inc     si                              ;point to next char in buffer

        call    _crc16                          ;calculate crc16
        dec     cx                              ;decrement counter
        jmp     char1

buf_end1:
        mov     es:byte ptr [si-2],0

        mov     _crc,bx                         ;save last crc16


        restore bp,ax,bx,cx,si,es  ; macro pop resgisters

        ret
_ck_crc16 endp


;*****************************************************************************
;*                                                                           *
;* ROUTINE      : crc16                                                      *
;*                                                                           *
;* PROGRAMMER   : CHAIPI WIJNBERGEN                                          *
;* LAST REVISED : 15.01.1986                                                 *
;*                                                                           *
;* INPUT        : AL = next char from buffer                                 *
;* OUTPUT       : BX = crc16 calculated & updated                            *
;*                                                                           *
;* DESTROYS     : none                                                       *
;*                                                                           *
;* CALLED BY    : make buf                                                   *
;* CALLING      : none                                                       *
;*                                                                           *
;*****************************************************************************

_crc16    proc   near

        xor     bh,ah

        mov     ah,bh

        shl     ah,1

        mov     al,0

        rcl     al,1

        xor     ah,bh

        rcl     ah,1

        rcl     al,1

        xor     al,bl

        test    bh,bh

        jpe     odd

        xor     ax,0380h

odd:    mov     bh,al
        mov     bl,ah
        ret

_crc16   endp
crc16_TEXT      ends

        END



                               \\\|///
                             \\  ~ ~  //
                              (  @ @  )
----------------------------oOOo-(_)-oOOo--------------------------------------
!                                                                             !
! Chaipi Wijnbergen                                                           !
! Electronics/Computer Eng. M.Sc.  Tel    : +972-8-9343079                    !
! Optical Imaging Laboratory       Fax    : +972-8-9344129                    !
! Brain Research Center            Email  : chaipi@tohu0.weizmann.ac.il       !
! Weizmann Institute of Science    URL    : http://www.weizmann.ac.il/~chaipi !
! Rehovot 76100 ISRAEL             IPhone : chaipi                            !
!                                                                             !
------------------------------------Oooo.--------------------------------------
                          .oooO     (   )
                          (   )      ) /
                           \ (      (_/
                            \_)