Need PC-AT "keyboard BIOS" docs

From: Ethan Dicks <>
Date: Thu Aug 29 20:04:00 2002

--- Tony Duell <> wrote:
> > > I am not sure where the term 'keyboard BIOS' came from, but it can go
> > > back there :-)
> >
> > I know it's a pre-programmed microcontroller, but in the U.S., if you
> > go to a PeeCee shop, that is what they call it.
> You mean you can actually buy them as loose chips? You have better PC
> shops that we do....

I doubt it, especially now that modern motherboards have integrated
the keyboard interface.

I did not mean to suggest that you could ever buy one loose, but if
you brought your machine in for service, that would be how they described
where the fault was if the keyboard didn't respond... i.e., "your
keyboard BIOS is fried."

> I assume you also realise that the 8042 outputs PC keyboard scan codes,
> and it's up to you to translate them into characters. This can be done in
> hardware (using an EPROM as a lookup table, and some logic to handle
> shift/control (you have to detect those scancodes and set/clear
> flip-flops for the shift/control status). It's possible, but not trivial.

That was the idea - a translator ROM.

> Of course there _are_ keyboards with plain async outputs [1] which would
> trivially link to the receiver side of your UART, but they are a lot less
> common than the PC/AT one.
> [1] Obvious examples : PERQ 2 keyboard, Xerox Daybreak keyboard, DEC
> LK201. You'd have to do a bit of hardware interfacing to convert signal
> levels, of course...

The LK201 emits ASCII not scan codes? Cool. I can handle that (or did
you just mean async characters at a reasonable baud rate?) I guess
I'll have to track down the docs to them. Converting the signal levels
is no big shake.



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Received on Thu Aug 29 2002 - 20:04:00 BST

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