Hex string checksum calculation

[chandra]

17 FE B3 50 02 B1 DE A8 0D E9 B6 D1 73
17 70 B3 50 02 B8 DE BB 0D CA B6 57 42
Both lines are Hex strings.The last two bytes are checksum values.Anybody can tell me the method how to calculate for that value.
Thanks

 

[_Eduardo_]

Only the last byte seem a checksum.

byte13 = 3F ^ byte1 ^ byte2 ^ ..... ^ byte12

^ mean exclusive OR


73 = 3F ^ 17 ^ FE ^ B3 ^ 50 ^ 02 ^ B1 ^ DE ^ A8 ^ 0D ^ E9 ^ B6 ^ D1

 

[chandra]

Thanks for reply.
From where you get the 3F.

 

[_Eduardo_]

The checksums are arbitrary operations. For example a XOR between the characters and a mask.

In this case the sample is very small (two lines of 13 characters), using XOR 0x3F (mask) verify these two cases, but it does not assure the solution.

 

[chandra]

I understand.Yes it is perfect with 3F.Thanks a lot.

 

[shaun5]

I have the same type problem and hoping for help!
I think the second to last hex is a checksum, but I can't figure out how to calculate it...
F0 0 61 0 0 7F 8 6F F7
F0 0 61 0 0 7F 9 70 F7
F0 0 61 0 0 7F A 6D F7
F0 0 61 0 0 7F B 6E F7
F0 0 61 0 0 7F 1B 7E F7
F0 0 61 0 0 7F 1C 7B F7
F0 0 61 0 0 7F 1D 7C F7
F0 0 61 0 0 7F 44 33 F7
F0 0 61 0 0 7F 7F 1A F7
F0 0 61 0 0 0 0 1A F7
F0 0 61 0 0 0 1 19 F7
F0 0 61 0 0 0 3C 36 F7
F0 0 61 0 0 0 78 72 F7
F0 0 61 0 0 1 11 A F7
F0 0 61 0 0 4 1F 13 F7
F0 0 61 0 0 4 2B 47 F7
F0 0 61 0 0 5 5E 53 F7
F0 0 61 0 0 7 68 7 F7

I think these would be calculated the same way, but can't be 100% sure:
F0 7F 61 00 09 03 08 75 F7
F0 7F 61 00 09 03 09 76 F7
F0 7F 61 00 09 3F 7E 2F F7
F0 7F 61 00 09 03 4C 31 F7

 

[shaun5]

I think the first and last values are start and stop markers..
Any ideas?