Sorry, no recommendation re: manufacturer, as I built my own (for ISA).

I cobbled together a bunch of gates whose output went high only when:
A24 (+A7), B28 (ALE) went HIGH; and A12 to A23 (+A19 to +A8), A25 to A31
(+A6 to +A0), and B13 (-IOW) went LOW.  If I've remembered everything,
that should happen ONLY when the system is writing to I/O Port 0080.

I used that signal to clock an eight-bit latch, which captured A2 to A8
(D7 to D0).  I used eight LEDs and some inverters (output LOW grounds
cathode to light LED) to display the POST code as binary.

For example, using DEBUG (entering ? after the - prompt gives a list of
the syntax), o0080 a0 should light the D7 and D5 LEDs like this:
*0*0 0000.   o0080 75 should give 0*** 0*0*.

I understand that the PS/2 uses I/O Port 0280 instead.

You also need a good listing of the POST codes for each BIOS that you
encounter, to interpret what the CPU was doing when the system failed.

If you enjoy working with those "plug-in-the-ICs" breadboard kits, and
have an old ISA daughterboard you are willing to sacrifice so that you
can use its contact strip to cable to the breadboard, this could be a
NEAT project.  Just in case of error, try it out on an old XT or the like.

Have fun!

Boyd Ramsay

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