Exar 22-908-03 anyone ?

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Mon May 31 13:47:16 2004

>
>
> Tony Duell heeft op maandag, 31 mei 2004 om 02:28 (Europe/Zurich) het
> volgende geschreven:
> >> It took out the 8035, a 74ls373 and, much worse, an unknown to me Exar
> >> IC 22-908-03, datecode 1983
> >
> > How many pins does this have?
>
> It is a 20 pin IC and it sits at the receiving end of the keyboard
> matrix, the other side of the matrix is driven by two 74138.

That's it, then. An octal latching sense amplifier IIRC.


>
> >
> > THis sounds a lot like one of the 2 semi-custom ICs used with a
> > Keytronics capacitive keyboard. I've seen 22-908-3B and 22-950-3B used
> > in
> > the PERQ 2 series and elsewhere. They have 20 pins each. The former is
> > the (latching) sense amplifier between the 8 keyboard row lines and an
> > 8
> > bit input on the microcontroller.
>
> It seems to be the exact same IC. The keyboard is indeed a Keytronics.

OK, at least we've identified it!


> >
> > You might be able to get a replacement for these from another
> > Keytronics
> > keyboard (e.g. a PC one).
> I'l start looking around..
> >
> >
> > I should be able to find pinouts for the PERQ keyboard ICs.
> I was hoping to kludge a replacement with some TTL's, but this might be
> difficult with a capacitive coupled keyboard.

It's more of a linear chip, in that it picks up the pulses from the
capacitive matrix. I have seen one such keyboard that was scanned in both
directions (yours isn't) and which used a 4051 analogue mux to scan the
row lines, the output of which was fed into a Motorola (I think) chip
designed as an FM radio IF amplifier (!). Needless to say making 8 such
amplifiers would be impractical for you.

I would start raiding old keyboards. I'd rather not raid one from an old
PERQ keyboard, though.

-tony
Received on Mon May 31 2004 - 13:47:16 BST