CRC-CCITT

Sun, 12 Oct 2003 23:48:07 -0700

I'm looking for assembler source code for the CRC-16 CCITT algorithm (poly 1021h). If you have code either for a 8051 derivate or for some Motorola MCU it would be great, but any assembler will be fine.

Thanks

Re: CRC-CCITT

Fri, 24 Oct 2003 13:55:22 -0700

: I'm looking for assembler source code for the CRC-16 CCITT algorithm (poly 1021h). If you have code either for a 8051 derivate or for some Motorola MCU it would be great, but any assembler will be fine.
:
: Thanks
:

No problem. Here's a fast lookup table version for 8051. This for the least-sig-bit-first variety of X^16+X^12+X^5+1, which is normal CCITT, and you append the result to the message in LSB-MSB order. I have it in several other assembler versions as well.

; Enter with R7:R6 initial CRC, DPTR pointer to data, R2 byte count
calc_crc:
	MOV	A,@DPTR			; get next data byte
	INC	DPTR
	PUSH	DPL			; save source data pointer
	PUSH	DPH
	XRL	A,R6			; XOR data with low CRC
	MOV	R6,A			; save for later
	MOV	DPTR,#crc_tab_lo	; point to low byte table
	MOVC	A,@A+DPTR		; get low byte
	XRL	A,R7			; XOR with high CRC
	XCHG	A,R6			; becomes new low CRC
	INC	DPH			; point to high byte table
	MOVC	A,@A+DPTR		; get high byte
	MOV	R7,A			; becomes new high CRC
	POP	DPH			; recover source pointer
	POP	DPL
	DJNZ	R2,calc_crc
	RET

crc_tab_lo:
	db	000h,089h,012h,09Bh,024h,0ADh,036h,0BFh
	db	048h,0C1h,05Ah,0D3h,06Ch,0E5h,07Eh,0F7h
	db	081h,008h,093h,01Ah,0A5h,02Ch,0B7h,03EH
	db	0C9h,040h,0DBh,052h,0EDh,064h,0FFh,076h
	db	002h,08Bh,010h,099h,026h,0AFh,034h,0BDh
	db	04Ah,0C3h,058h,0D1h,06Eh,0E7h,07Ch,0F5h
	db	083h,00Ah,091h,018h,0A7h,02Eh,0B5h,03Ch
	db	0CBh,042h,0D9h,050h,0EFh,066h,0FDh,074h
	db	004h,08Dh,016h,09Fh,020h,0A9h,032h,0BBh
	db	04Ch,0C5h,05Eh,0D7h,068h,0E1h,07Ah,0F3h
	db	085h,00Ch,097h,01Eh,0A1h,028h,0B3h,03Ah
	db	0CDh,044h,0DFh,056h,0E9h,060h,0FBh,072h
	db	006h,08Fh,014h,09Dh,022h,0ABh,030h,0B9h
	db	04Eh,0C7h,05Ch,0D5h,06Ah,0E3h,078h,0F1h
	db	087h,00Eh,095h,01Ch,0A3h,02Ah,0B1h,038h
	db	0CFh,046h,0DDh,054h,0EBh,062h,0F9h,070h
	db	008h,081h,01Ah,093h,02Ch,0A5h,03Eh,0B7h
	db	040h,0C9h,052h,0DBh,064h,0EDh,076h,0FFh
	db	089h,000h,09Bh,012h,0ADh,024h,0BFh,036h
	db	0C1h,048h,0D3h,05Ah,0E5h,06Ch,0F7h,07Eh
	db	00Ah,083h,018h,091h,02Eh,0A7h,03Ch,0B5h
	db	042h,0CBh,050h,0D9h,066h,0EFh,074h,0FDh
	db	08Bh,002h,099h,010h,0AFh,026h,0BDh,034h
	db	0C3h,04Ah,0D1h,058h,0E7h,06Eh,0F5h,07Ch
	db	00Ch,085h,01Eh,097h,028h,0A1h,03Ah,0B3h
	db	044h,0CDh,056h,0DFh,060h,0E9h,072h,0FBh
	db	08Dh,004h,09Fh,016h,0A9h,020h,0BBh,032h
	db	0C5h,04Ch,0D7h,05Eh,0E1h,068h,0F3h,07Ah
	db	00Eh,087h,01Ch,095h,02Ah,0A3h,038h,0B1h
	db	046h,0CFh,054h,0DDh,062h,0EBh,070h,0F9h
	db	08Fh,006h,09Dh,014h,0ABh,022h,0B9h,030h
	db	0C7h,04Eh,0D5h,05Ch,0E3h,06Ah,0F1h,078h
; follow right on here, exactly 256 bytes after crc_tab_low
crc_tab_hi:
	db	000h,011h,023h,032h,046h,057h,065h,074h
	db	08Ch,09Dh,0AFh,0BEh,0CAh,0DBh,0E9h,0F8h	
	db	010h,001h,033h,022h,056h,047h,075h,064h	
	db	09Ch,08Dh,0BFh,0AEh,0DAh,0CBh,0F9h,0E8h
	db	021h,030h,002h,013h,067h,076h,044h,055h
	db	0ADh,0BCh,08Eh,09Fh,0EBh,0FAh,0C8h,0D9h
	db	031h,020h,012h,003h,077h,066h,054h,045h
	db	0BDh,0ACh,09Eh,08Fh,0FBh,0EAh,0D8h,0C9h
	db	042h,053h,061h,070h,004h,015h,027h,036h
	db	0CEh,0DFh,0EDh,0FCh,088h,099h,0ABh,0BAh
	db	052h,043h,071h,060h,014h,005h,037h,026h
	db	0DEh,0CFh,0FDh,0ECh,098h,089h,0BBh,0AAh
	db	063h,072h,040h,051h,025h,034h,006h,017h
	db	0EFh,0FEh,0CCh,0DDh,0A9h,0B8h,08Ah,09Bh
	db	073h,062h,050h,041h,035h,024h,016h,007h
	db	0FFh,0EEh,0DCh,0CDh,0B9h,0A8h,09Ah,08Bh
	db	084h,095h,0A7h,0B6h,0C2h,0D3h,0E1h,0F0h
	db	008h,019h,02Bh,03Ah,04Eh,05Fh,06Dh,07Ch
	db	094h,085h,0B7h,0A6h,0D2h,0C3h,0F1h,0E0h
	db	018h,009h,03Bh,02Ah,05Eh,04Fh,07Dh,06Ch
	db	0A5h,0B4h,086h,097h,0E3h,0F2h,0C0h,0D1h
	db	029h,038h,00Ah,01Bh,06Fh,07Eh,04Ch,05Dh
	db	0B5h,0A4h,096h,087h,0F3h,0E2h,0D0h,0C1h
	db	039h,028h,01Ah,00Bh,07Fh,06Eh,05Ch,04Dh
	db	0C6h,0D7h,0E5h,0F4h,080h,091h,0A3h,0B2h
	db	04Ah,05Bh,069h,078h,00Ch,01Dh,02Fh,03Eh
	db	0D6h,0C7h,0F5h,0E4h,090h,081h,0B3h,0A2h
	db	05Ah,04Bh,079h,068h,01Ch,00Dh,03Fh,02Eh
	db	0E7h,0F6h,0C4h,0D5h,0A1h,0B0h,082h,093h
	db	06Bh,07Ah,048h,059h,02Dh,03Ch,00Eh,01Fh
	db	0F7h,0E6h,0D4h,0C5h,0B1h,0A0h,092h,083h
	db	07Bh,06Ah,058h,049h,03Dh,02Ch,01Eh,00Fh
; end of table

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