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While working with the GAL16V8 (an old programmable logic device), I found out that the Programmers Electronic Signature (PES) of each GAL has a checksum byte

I've read the PES of some GALs but was unable find out the kind of checksum used. In the sequences below, the last byte is supposed to be the checksum.

00 03 1A A1 00 00 00 30
00 05 50 A1 CD A6 03 06
00 05 1A A1 CD A4 03 06
00 02 1A 8F 00 00 00 15
00 02 1A 81 00 00 00 10

How do I identify the checksum method used?

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If you can't find documentation indicating the checksum algorithm, you could try reversing the software that reads or writes the checksum. I'm not familiar with GAL, but from the site you linked, there are references to programming software [1] which should be writing the checksum or verifying it before programming the chip.

[1] http://www.armory.com/~rstevew/Public/Pgmrs/GAL/intro.htm

| improve this answer | |
  • unfortunately this is the checksum of something that is on a special part of the chip that doesn’t get reprogrammed, so you don’t need to recompute it when verifying. – dwery Jul 7 at 7:56

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