Reading PALs

[Chuck Guzis]

On 02/18/2017 04:22 PM, Jim Brain wrote:
> Seems like someone on list was willing and able to read PAL16L8s and 
> give a try to some PAL16R4s...  Is that person still on list and
> still interested?  If so, please contact me off-list.
> 
> I am trying to restore some C64 carts, and the PAL on my working unit
> is protected, so I cannot replicate.

If I'm the person (see  my blog on vcfed.org), "reading" isn't exactly
the right term.  For purely combinatorial PALs, the technique is to
determine the input and output assignments, then exhaustively run
through all the combinations.  Take that data and run it through a logic
minimizer, such as Logic Friday and then  use a bit of wetware to pick
out tristate control lines and their corresponding outputs.

Not foolproof by any means--and much less so, if the device is
registered, but very often successful.

A schematic showing the part application can be a godsend.

--Chuck