http://mcosre.sourceforge.net/docs/adb_connector.html
11/2/2004

	D o c u m e n t a t i o n  ADB Connector
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The ADB is a single-master, multiple-slave serial communications bus that uses an asynchronous protocol and connects keyboards, graphics tablets, mouse devices, and other devices to the computer.

The custom ADB microcontroller drives the bus and reads status from the selected external device. A 4-pin mini-DIN connector connects the ADB to the external devices.

Notes:
        1. The total current available for all devices connected to 
           the +5 V pins on the ADB and the modem port is 500 mA. 
           Each device should use no more than 100 mA.
           
        2. The user must hold down a key combination for at least 
           1 second to allow the ADB microcontroller enough time 
           to respond to the NMI or hard-reset signal.

ADB connector pin assignments
--------------------------------------------------

 Pin # | Name | Description
=======+======+===================================
   1   | ADB  | Bidirectional data bus used for 
       |      | input and output. It is an 
       |      | open-collector signal pulled up 
       |      | to +5 volts through a 470-ohm 
       |      | resistor on the main logic board.
-------+------+-----------------------------------
   2   | PSW  | Power-on signal that generates 
       |      | reset and interrupt key 
       |      | combinations.
-------+------+-----------------------------------
   3   | +5V  | +5 volts from the computer.
-------+------+-----------------------------------
   4   | GND  | Ground from the computer.