From Trammell Hudson's Projects

ADB to USB adapter

Mac SE with a BeagleBone Black motherboard

Older Macintosh computers used the Apple Desktop Bus protocol to communicate with keyboards and mice. It is a one-wire, bidirectional multi-drop protocol.

ADB adapter

adb2usb arduino sketch for the Teensy 2.0

Apple ADB keyboard and mouse interface

ADB is self clocking on the falling edge -- a Zero is a low of 65 ns and high of 35 ns, and a One is a low of 35 ns followed by a high of 65 ns -- for a total of 100 microseconds per bit.