4: GND
-
Commands
--------
ADB command is 1byte and consists of 4bit-address, 2bit-command
You can read the state from PSW line(active low) however
the switch has a special scancode 0x7F7F, so you can
also read from Data line. It uses 0xFFFF for release scancode.
+ Release code seems to delay about some 100ms. Due to Mac soft power?
Keyboard LEDs & state of keys(Register2)
This register hold current state of three LEDs and nine keys.