Need PC-AT "keyboard BIOS" docs

From: Ethan Dicks <>
Date: Wed Aug 28 12:35:01 2002

I had this idea for a keyboard adapter for classic machines, but I
don't understand the 40-pin "keyboard BIOS" microcontroller well
enough to know if it's possible...

The idea is this - a PS/2-keyboard to RS-232 converter - plug in
any AT- style keyboard, hook the other end into the receive pin of the
target's console port. I started from a) a microprocessor-based
OMNIBUS peripheral and wanted to put an LCD or VFD on it for
status and control. Then I decided I wanted to be able to
_talk_ to the embedded processor, not just listen, but without
the bulk and hassle of a dedicated VT100 or laptop. If I could
cobble up a simple way to turn PS/2-style keyboard strokes into
9600 baud ASCII characters, I could leave that circuit in place
and plug in a keyboard as needed.

I know that the 6402 serial chip can be strapped to operate in a
dumb converter mode - I've seen it used in GPIB<->serial boxes
for the PET with no microcontroller in the box. Depending on
the microprocessor-facing end of an AT "keyboard BIOS" chip, I
was thinking that you could pull one from an old motherboard
(that still had them independent from the core chipset), run
the scan codes through a translator EPROM, use the "release"
scan codes as a trigger to a latch that would hold the character
in place for the 6402 to send. Three major chips and about an
afternoon of point-to-point wiring, maybe a TTL part or two,
to drive the keyboard and maybe trigger the UART.

Does this sound like a reasonable approach? I'm not opposed to
using a PIC or Atmel microcontroller, but a no-CPU approach
with stuff from my junk box is especially appealing. I have
a lifetime supply of low density EPROMs, a stack of 6402s and
old motherboards with removable keyboard chips. Just not sure
it's possible since I don't understand the keyboard chip at the

So... is there a good place (on the web) to learn about the
"keyboard BIOS" chip? Alternatively, is there already a project
like this that I can clone? If anyone has any examples of how
to attach a PeeCee keyboard to a 68000 or 6502 directly, without
going through a UART, I guess I'd be interested in that, too; but
since I was already planning on sticking a Z8530 or 6551 or 16550
chip on the OMNIBUS board anyway, I might as well use the same
serial port for all embedded console I/O.

Thanks for any pointers,


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Received on Wed Aug 28 2002 - 12:35:01 BST

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