backing up PAL chips

25 Jun 2006

...

   Advice
appreicated :) I'm used to working with EPROMs, but PALs are a
 total unknown to me!  Keep it all --- I don't think you need more than a floppy
disk at one time
 for all the software and data files for the older PAL's.  
     this is a good question: How to reverse-engineer PALs?

     Maybe a simple all-possibilities-generator on all the inputs could lead
 me to derive the logical map? 
That works if the PAL is purely combinatorial (or with a slight 
modification, if the outputs are latched (registered), but with no 
feedback from the outputs into the AND matrix).

The problem comes that many PALs allow the outputs to be internally fed 
back into the AND matrix. Which means you can make flip-flops and other 
sequential stuff. In which case a brute-force 'try all the inputs, grab 
the outputs, apply logic reduction' doesn't work.

-tony

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backing up PAL chips