SX Specific Cyclic Redundancy Check

16 Bit - Super Fast

By Nikolai Golovchenko

```        DEVICE  SX28L, OSCHS2, TURBO, STACKX, OPTIONX
RESET start

ORG \$08         ;global bank

temp    DS 1
crc_hi  DS 1
crc_lo  DS 1
count	DS 1

;x^16+x^15+x^2+x^0
;CRC_POLY_HIGH   EQU \$80
;CRC_POLY_LOW    EQU \$05

;X^16+X^12+X^5+1   (CCITT polynomial)
CRC_POLY_HIGH   EQU \$10
CRC_POLY_LOW    EQU \$21

;************************************************************************

start

;initialize CRC
call    crc_init        ;CRC = 0000

;calculate CRC for data example:
;01,75,8A,0B,2E,B4
mov     w, #\$01
call    crc_update      ;CRC = 1021
mov     w, #\$75
call    crc_update      ;CRC = 1D03
mov     w, #\$8A
call    crc_update      ;CRC = F05E
mov     w, #\$0B
call    crc_update      ;CRC = 0074
mov     w, #\$2E
call    crc_update      ;CRC = B1AC
mov     w, #\$B4
call    crc_update      ;CRC = FCA5
;final CRC value is FCA5

;check the following CRC - result should be zero
mov     w, #\$FC
call    crc_update      ;CRC = A500
mov     w, #\$A5
call    crc_update      ;CRC = 0000
;check passed!

jmp 	\$

;************************************************************************
;
; Initialize CRC checksum (to zero)
;
;************************************************************************
crc_init
clr 	crc_lo
clr 	crc_hi
retp

;************************************************************************
;
; Update CRC checksum with new data in W. MSb goes first.
;
;************************************************************************
crc_update
mov     temp, w         ;save data in temp
mov     w, #8           ;init counter
mov     count, w        ;
crc_loop
;XOR the carry (MSb of CRC) and the next bit of data (starting from
;MSb). If result is zero, don't invert any bits in the checksum.
;If result is one, invert the checksum bits as determined by the
;polynomial.

mov     w, temp
and	w, #\$80
xor     crc_hi, w

clc                     ;Rotate CRC one place left and
rl      crc_lo          ;move the MSb to carry
rl      crc_hi          ;

sc                      ;check the result
jmp    crc_next        ;skip inversion if result is zero

mov     w, #CRC_POLY_HIGH       ;higher byte of polynomial
xor     crc_hi, w
mov     w, #CRC_POLY_LOW        ;lower byte of polynomial
xor     crc_lo, w
crc_next
rl      temp            ;prepare next bit
decsz   count
jmp    crc_loop
ret
;************************************************************************

```

 file: /Techref/scenix/lib/io/osi2/crc16-ng.htm, 3KB, , updated: 2001/5/19 20:40, local time: 2024/9/18 22:27, TOP NEW HELP FIND:  18.205.56.209:LOG IN

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