Well, here's a start... It only applies to PALs with no burried flip-flops -- that is it only works for chips where a change of internal state is visible on the pins. This applies to the classic PALs, but not necessarily to GALs (from what I rmember). What you need is a device that has a fair number of TTL I/O lines (alas few modern computers have user ports or hacker-friendly buses, but anyway). You want to be able to drive each input of the PAL under test and read all the outputs (I asusme you know which pins are inputs and which are outputs, from the schematic if nowhere else). The first thing to do is to indentify which (if any) outputs show sequential (i.e. internal latch/flip-flop) behaviour. In pseudocode it goes like this set all output_states to COMBINATORIAL for inputs=0 to (2^no_of_inputs)-1 do write(inputs) outputs_1= read (outputs) for this_input = 0 to no_of_inputs-1 do invert this_input invert this_input /* this toggles each input in turn and sets it back to the original state */ new_outputs=read_outputs if new_outputs!=outputs_1 then set output_states for outputs that changed to SEQUENTIAL At the end of this, you will hopefully have some combinatorial outputs. Then, try all possible input states again, record the outputs and look at those that are known to be combinatorial. Use your favourite logic minimalisation method to produce the logic equations for those. That's part 1. I will think about cracking sequential terms... TAoE calles this 'Security through solder' or soemthing similar. I've never desoldered a GAL. I've desoldered _many_ DIL-packaged PALs without damage. It depends on how good you are at soldering. If you're happy removing other ICs without problems, I don't think you'll have any problems with PALs/GALs -tony