How exactly do PAL chips get programmed?

[Tony Duell]

> 
> So if I have the original code and know what chip it needs to be programmed
> on I might be in luck, otherwise there is little hope?

If you have the original, working, chip, it's worth sticking it into a 
programmer that supports that chip and manufacturer and trying to read 
it. 

Some manufactuerers did not copy-protect their PALs. For example, all the 
PALs in the VAX 11/730 CPU are readable (for all they're the key to the 
design). All PALs in every PERQ I've seen (including the AGW3300) are 
readable. All PALs in the Torch XXX -- apart from those on the (3rd 
party?) 68020 kludgeboard -- are readable. But then again, most PALs on 
clone ISA boards are protected.

If the original chip is a HAL, you are out of luck. HAL == Hard Array 
Logic, it's a mask-programmed equivalent to a PAL. I've never found one 
that can be read out, I suspect the circuitry simply isn't there.

-tony