Finding out checksum algorithm

Question

I have old serial communication protocol and having some trouble finding out about checksum algorithm that has been used. I've tried several CRC16 algorithms and none of them seem to work.

Tx message format looks like:

start(10B) + messageIndex(1B) + data(5-15B) + checksum(2B) + end(1B) 

Rx message has same format but only 1 data byte. Here are few examples provided (hash # added to separate the blocks; hexadecimal format):

Tx: 82 00 00 00 01 00 00 00 ff c1 # 48 # 56 57 50 41 54 5f 30 5f 31 3d 31 # 7f 12 # 83
Rx: 82 00 00 00 ff 00 00 00 01 01 # 48 # 4f # cc 68 # 83

Tx: 82 00 00 00 01 00 00 00 ff c1 # 49 # 56 57 50 41 4e 5f 30 5f 32 3d 49 55 30 30 30 # f5 16 # 83
Rx: 82 00 00 00 ff 00 00 00 01 01 # 49 # 4f # 5c 69 # 83

Tx: 82 00 00 00 01 00 00 00 ff c1 # 4a # 56 57 50 41 54 5f 30 5f 32 3d 31 # b8 1b # 83
Rx: 82 00 00 00 ff 00 00 00 01 01 # 4a # 4f # ac 69 # 83

Tx: 82 00 00 00 01 00 00 00 ff c1 # 4b # 56 57 41 4b 54 50 4e 5f 30 3d 32 # 60 6f # 83
Rx: 82 00 00 00 ff 00 00 00 01 01 # 4b # 4f # 3c 68 # 83

Tx: 82 00 00 00 01 00 00 00 ff c1 # 4c # 56 57 50 41 4e 5f 31 5f 31 3d 49 4c 30 30 30 # 6a ec # 83
Rx: 82 00 00 00 ff 00 00 00 01 01 # 4c # 4f # 0c 6a # 83

If necessary, I can provide more data. Any help or hint would be appreciated ;)

Best regards, Zlatko

EDIT The correct algorithm is regular CRC16 (0x8005 polynom). Thanks booto for correct answer.

Answer 1

It's a big-endian CRC16 (polynomial 0x8005) of the data from the byte following the 0x82 up to and including the byte before the CRC.

For example, for your last RX frame:

82 00 00 00 ff 00 00 00 01 01 4c 4f 0c 6a 83

The CRC16 of {0x00,0x00,0x00,0xff,0x00,0x00,0x00,0x01,0x01,0x4c,0x4f} is 0x0c6a.

To find out this CRC algorithm, I assumed that 0x82 was a 'Start-of-Frame' marker and 0x83 was an 'End-of-Frame' marker. Then, I plugged the remaining data (sans crc field) into this on-line CRC calculation application and the emitted CRC16 looked correct.

I, then, checked a few of the other frames you supplied and verified the CRC calculation with other sources.

And, voila...