My source is the Atari ST style keyboard interface, I am of two minds if I am going to use the Atari ST encoding scheme or if I should make my own.

This means that the keyboard has a micro-controller that encodes the keyboard presses in to serial, TTL-232, and that the keyboard can handle really slow IO like RTC and joysticks as well.

http://didierm.pagesperso-orange.fr/eiffel-e.htm <-- example controller for the Atari ST