PAL replacement

keithpjrc

Member
Hello!

I want to create a small proof of concept replacement for a PAL which I'm currently reverse engineering. This is a 20pin DIP TIBPAL16L8-25CN. Its worst case propagation delay is 25ns. The PAL is faster than the application needs, which I'm still trying to characterize. There are something like 12 or 13 inputs, and 6 outputs. The output pulses are around 340ns wide, which puts the maximum frequency around 3.5mhz +/-.

The teensy would have to recognize a change in the inputs, and either a nested if/switch/case/lookup table, determine the outputs. I could probably break the logic up so that the fast-read-loop pre-qualified the inputs.... meaning read only a few bits, and only pay the time penalty of reading the other inputs and looking up, if that initial criteria was met.

I already own a couple Teensy's. Maybe a 3.1 or 3.2?

Eventually going to write equations and write a GAL --- but would like to prove out my logic now.

Is the teensy in the ballpark capable of doing this?

Thanks!
 
I've managed to reverse engineer the equations for the PAL. I wrote a python function that takes input bits, and returns outputs.

I'd think the arduino code might look like series of (12) digitalreadfast()'s, and then (6) digitalwritefast()'s which use binary operators between some of the input bits.

I wonder how fast I can execute (18) reads/writes and what the propagation delay would be from read change to write change.

The output is only valid for 340ns, but the next set of input bits would be around 2.75us later.

Any thoughts on this?
 
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