Sources for 8b TTL keyboards (Keytronics)

[Tony Duell]

> It's weird, that... I suspect I could rustle up something 
> 'traditional' around 
> a Z80/6502, ROM, RAM and some decoding - but my brain just doesn't cope well 
> with single-chip 'black boxes' such as PIC-based widgets. I really 
> don't know why! 

My problem with single-chip microcontrolelrs (PICs, etc) is trying to 
debug the firmware. If I have external program memory, I can hang a logic 
analyser off said memory's address bus and see just what the firmware is 
doing. But there's no way to really trace the code running in a PIC. 

OK, you can add instructions to set/reset 'spare' port pins at particular 
points in the code and see if/when those change. But it's nowhere near as 
convenient as being able to trace the code.

I can't afford the real ICE units for the PIC, etc.

And please don't suggest the simulator. I've never found a simulator that 
(a) I trust and (b) allows me to correctly simulate all the exernal 
hardware I have hanging off the microcontroller.

-tony