[DUG] Checksums

[Marshland Engineering]

Does anyone know about checksums ?

I'm reverse engineering some CNC code and I can't seem to find out how it works.

R22302230100000000049900000000B900000000F900031367D90000000040000000277F4F00
R22302230100000000049900000000B900000000F900031367D900000000400000004F7F2700

Note the format seems to be 8 digits and 2 code, so 99  B9  F9  D9  40  F4 are function codes. The 8 digits are the numeric values. 


These are 2 lines of code. I think the last 2 non zero digits are the checksums, 4F and 27.

This is a drill command and the only differences between commands is ones feed is 100 and the other 200. I think this is reflected in 27 and 4F before the 7F. The is common to all CNC commands. 

What is interesting is the Checksum for the first line is 4F with a feed of 27 and the second is 27 with a feed of 47. By this I take it they are using ones compliment checksum routines. 

Any ideas ?

(Bring out those Commodore 64 programmers.)

Cheers Wallace
 
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