Little cheating Babel fish

A project log for Gigatron TTL microcomputer

Just because! A home computer without microprocessor

Marcel van KervinckMarcel van Kervinck 06/07/2018 at 21:592 Comments

There are several methods brewing for hooking up a keyboard. The one most in line with the system is WattSekunde's four chip design for a matrix keyboard interface. But such keyboards might be hard to find, while PS/2 keyboards are still easy to get. But their protocol is convoluted and it is unclear how to handle that with a few simple logic chips. So... we cheat!

PS/2 is simply too modern, and we need a time machine to translate its fast and complex signals to the simple signals that the Gigatron will understand. The ATtiny85 will be our Babel fish.

To get some idea: the ATtiny85 must be configured to run at 8 MHz to do its magic. 1 MHz won't be good enough to catch and transfer simple key strokes. Here is the system in action:


Justin Davis wrote 06/08/2018 at 14:58 point

Very neat and compact!  But if you're going to cheat by using a micro, then you might as well bring it up to the modern keyboard standard USB.  I believe you can do it with a single micro as well, but maybe not as elegant as the 8-pin ATtiny.  This is probably why so many early computers had their keyboards built-in (maybe in the Gigatron 2?)

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Marcel van Kervinck wrote 06/09/2018 at 10:27 point

That was the previous phase, but it used an Arduino Uno and that has two micro controllers, one for the USB. Next step is to remove the PS/2 guts from the keyboard and drive the matrix from TTL :-)

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