General Instruments Capacitive Keyboard Encoder

[Paul Birkel]

> -----Original Message-----
> From: Tony Duell [mailto:ard.p850ug1 at gmail.com] 
>
> On Wed, May 5, 2021 at 8:12 AM Paul Birkel <pbirkel at gmail.com> wrote:
> >
> > > -----Original Message-----
> > > From: Tony Duell [mailto:ard.p850ug1 at gmail.com]
> > >
> > > > On Tue, May 4, 2021 at 10:33 AM Paul Birkel via cctalk <cctalk at classiccmp.org> wrote:
> > > >
> > > > The GI encoder is a DIP-40 labeled as "321239007  M2406-054-02  GI 8233 CBU
> > > > TAIWAN".  I seek technical documentation for this IC.
> > >
> > > You might take a look at the manuals here :
> > >
> > > http://cpu-ns32k.net/Whitechapel.html
> > >
> > > I am pretty sure there's a keyboard techincal description in 'binder
> > > 1' and a reverse-engineered schematic in 'binder 2'. While it's not
> > > quite the same IC, it's related and the power pins are in the right
> > > place :-)
> > >
> > > Alas there is no real description of what that IC does or how to talk
> > > to it from the 8039. It is designed to sit on the 8039 bus, it takes
> > > in the multiplexed address/data bus, ALE, rd/ and wr/
> >
> > The straight-thru wiring on ~RD and ~WR alongside ALE with no address decoding is IMO 
> > rather odd.  I wonder how that design actually works (either assumes that it is the only writable 
> > device present, or actually latches 8 bits of address and shadows some valid ROM address) 
> > and then what gets written to the encoder for what purpos(es). 
>
> Remember that the 8039 has separate program and data memory spaces.

"Sokath, his eyes uncovered."  Thank you Tony.  Your notation observations both sound very reasonable to me.

paul