On 5/22/07, Rod Smallwood <RodSmallwood at mail.ediconsulting.co.uk> wrote:
Hi
I have just remembered how the later version keyboards worked.
It was still a counter sytem but the values where fully decoded.
It worked on a matrix system.
Each key on the keyboard sat across the junction of one of the matrix
points.
Thanks for those technical tidbits, Rod. What you wrote resonates
with what I remember of my explorations of 15 years ago. The UARTs in
the keyboards were of the type that worked like a PISO shift register,
but with start and stop bits "for free"; no CPU required to set up the
UART - all pin-selectable options (like the INS6402, as I said). I'll
have to cast a careful eye at how the matrix ties into the UART and I
think this will all make more sense.
Since I first tried to tackle this, I've spent a lot of time reading
the "CMOS Cookbook" and the "TTL Cookbook" - lots of strange
counter-based things in there. I was just learning how logic devices
functioned back in their heyday, so I'm OK with straightforward uses,
but some of the really clever tricks I have to study before I get.
Thanks again, Rod.
-ethan