006
23.10.2010, 18:36 Uhr
volkerp
Default Group and Edit
|
Im originalen Brenn-Programm von robotron wird CRC-CCITT / CRC-16 (x16 + x12 + x5 + 1) genutzt. Der Startwert ist 0xFFFF.
| Quellcode: | ; CRC berechnen
crc: ld hl, 0FFFFh
crc1: ld a, (de)
xor h
ld h, a
rrca
rrca
rrca
rrca
and 0Fh
xor h
ld h, a
rrca
rrca
rrca
push af
and 1Fh
xor l
ld l, a
pop af
push af
rrca
and 0F0h
xor l
ld l, a
pop af
and 0E0h
xor h
ld h, l
ld l, a
inc de
dec bc
ld a, b
or c
jr nz, crc1
ret
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und als Perl-Programm
| Quellcode: | #CRC-CCITT (CRC-16) x16 + x12 + x5 + 1
$POLY = 0x8408; # 16-12-5-1
#this is the CCITT CRC 16 polynomial X^16+X^12+X^5+1
#This works out to be 0x1021, but the way the algorithm works
#lets us use 0x8408 (the reverse of the bit pattern). The high
#bit is always assumed to be set, thus we only use 16 bits to
#represent the 17 bit value.
#1 0001 0000 0010 0001 16-12-5-1
#1000 0100 0000 1000 1 reverse -> 0x8408h
#Startwert
$crc16 = 0xFFFF;
for ($i=0;$i<$len;$i++) {
my $bits = ord(substr($buf,$i,1));
for (0..7) {
if (($bits & 1) ^ ($crc16 & 1)) {
$crc16 >>= 1;
$crc16 ^= $POLY;
} else {
$crc16 >>= 1;
}
$bits >>= 1;
}
}
printf "CRC = %.4X\n", $crc16;
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--
VolkerP
http://hc-ddr.hucki.net
(Z9001, Z1013, LC-80, ...) |
