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Sun, 7 Feb 1999 05:04:14 -0500 |
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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
[log in to unmask]
PCBUILD's List Owner's:
Bob Wright<[log in to unmask]>
Drew Dunn<[log in to unmask]>
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