Reading PALs

[Chuck Guzis]

On 02/21/2017 02:06 PM, Mattis Lind wrote:

> But now it solved because Kelly Leavitt somehow did find the correct
> link, which is not the one linked to from the page. Thanks a lot for
> this!
> 
> Unfortunately there were no source code in there unless they are
> self extracting binaries. No PC nor DOSEMU running so I cannot check
> right now. If there are no source I need to try to figure out the the
> ordering of the pins that the dump uses from the schematic. It seems
> not to readable by the version of Eagle I have here though.
> 
> Maybe it will be easier to DIY anyway...
> 
> Anyone else that done this kind of PAL analysis so I can avoid
> reinventing the wheel?


If you check my vcfed.org blog, you'll see that I used a PC parallel
port to drive a setup pretty much consisting of a few 74LS193 counters
and a 74LS151 multiplexer, driven off the low 4 bits of the counters.
This gave me 20 bits of output, so I took some of the extra bits and
used them to "push" possible tristate bits through 2K resistors. One
parallel printer bit to reset, another to count and one to read the output.

Built in an evening with parts from my hellbox on a hunk of perfboard.
I was tempted to use an MCU, but given the 20 outputs+4 inputs of this
rig, it made more sense.

--Chuck