Date   : Wed, 23 Oct 2002 21:42:13 +0100
From   : Sprow <news@...>
Subject: Re: BBC keyboard playing up

In article <10210232110.ZM8916@...>,
   Pete Turnbull <pete@...> wrote:
> > In article <38cd6894b%mjfoot@...>,
> >    Michael Foot <mjfoot@...> wrote:

> > > Has anyone encounted this type of behavour before? What ICs control the
> > > signals to/from the keyboard?
> >
> > The system via (you could try swapping this with the less useful user
> > via) and the shift register on the keyboard itself,talking to eachother 
> > over the not-so-reliable grey molex cable,

> What shift register?  There's no shift register involved anywhere in the
> keyboard circuit.
>
> It works like this:
>
> A 74LS161 (or 74163, they're interchangable for this purpose) 4-bit
> pre-loadable counter is clocked at 1MHz

Silly me,it was a counter.
There were multiple outputs and a clock pin,and LS161 didn't spring to mind
as one of the counters I knew so concluded it was a parallel loading shift
register: rather sloppy since the TTL databook is just over the other side
of the room!

Sprow.