CRC16 checksum: HCS08 vs. Kermit vs. XMODEM

Question

I\'m trying to add CRC16 error detection to a Motorola HCS08 microcontroller application. My checksums don\'t match, though. One online CRC calculator provides both the resu

Answer 1

X-Modem 1K CRC16.

Process for bytewise CRC-16 using input data {0x01, 0x02} and polynomial 0x1021

1. Init crc = 0

2. Handle first input byte 0x01: 2.1 'Xor-in' first input byte 0x01 into MSB(!) of crc: 0000 0000 0000 0000 (crc) 0000 0001 0000 0000 (input byte 0x01 left-shifted by 8)

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   0000 0001 0000 0000 = 0x0100 The MSB of this result is our current divident: MSB(0x100) = 0x01. 2.2 So 0x01 is the divident. Get the remainder for divident from our table: crctable16[0x01] = 0x1021. (Well this value is famila from the manual computation above.) Remember the current crc value is 0x0000. Shift out the MSB of current crc and xor it with the current remainder to get the new CRC: 0001 0000 0010 0001 (0x1021) 0000 0000 0000 0000 (CRC 0x0000 left-shifted by 8 = 0x0000)

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   0001 0000 0010 0001 = 0x1021 = intermediate crc.

3. Handle next input byte 0x02: Currently we have intermediate crc = 0x1021 = 0001 0000 0010 0001. 3.1 'Xor-in' input byte 0x02 into MSB(!) of crc: 0001 0000 0010 0001 (crc 0x1021) 0000 0010 0000 0000 (input byte 0x02 left-shifted by 8)

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   0001 0010 0010 0001 = 0x1221 The MSB of this result is our current divident: MSB(0x1221) = 0x12. 3.2 So 0x12 is the divident. Get the remainder for divident from our table: crctable16[0x12] = 0x3273. Remember the current crc value is 0x1021. Shift out the MSB of current crc and xor it with the current remainder to get the new CRC: 0011 0010 0111 0011 (0x3273) 0010 0001 0000 0000 (CRC 0x1021 left-shifted by 8 = 0x2100)

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   0001 0011 0111 0011 = 0x1373 = final crc.