Apple Desktop Bus



Apple Desktop Bus

ADB [Apple Desktop Bus] was a serial bus used by Apple computer to drive the mouse and keyboard.
The cable consisted of one bidirectional data line [pin 1], a +5 volt power line [pin 3] and a ground line [pin 4].
Some systems also used a power-up line on pin 2.
The ADB interface could supply up to 200mA of current [500mA max] to the Peripheral device.
The maximum data rate was 125kbps, actual bus speed was much lower.
The bus has a relatively low bandwidth, and, given the packet structure, the theoretical maximum bandwidth is on the order of 100 - 200 bytes/second.
The ADB interface is an Open Collector bus, Data line [pin 1].
How to calculate the value of an Open Collector Pull-Up Resistor.

The maximum cable length was 5 meters, using a Mini-DIN 4 pin male connector.
However 6 feet and 12 feet straight or coiled cable lengths are common. Keyboard cables are normally Male-to-Male cables.
The ADB bus is OBSOLETE and was replaced by the Firewire bus.
ADB to USB adapter cables are also produced allowing older peripheral devices to be used with newer MAC computers.





Soft Power [Pin 2]
On a Macintosh with software power control, the machine can be turned on by an ADB device.
This is accomplished by momentarily connecting pin 2 on the ADB connector (reserved) to pin 4 (ground).
Pin 2 should be kept grounded until pin 3 (+5 volts) comes up to power, letting you know that the machine has actually come on.
Some Macintosh machines do not have soft-power capabilities; on these machines, grounding pin 2 will have no effect.

ADB DIN connector pin out and outline
ADB Mouse Pin Out
Pin NumberPin Function
1Data
2Power up
35 volt
4Ground

ADB Panel Connector

4-pin MiniDin cables are still available, MAC ADB Cable styles;

MiniDin4 Male / MiniDin4 Female, 4C, 6 foot cable
MiniDin4 Male / MiniDin4 Male, 4C, 10 foot cable
MiniDin4 Male / MiniDin4 Male, 4C, 6 ft cable

ADB computer side connector graphic.
Circular DIN examples [graphics]
Circular DIN Connector Vendors [Manufacturers]

All other Apple interfaces are listed on the Apple Computer Buses page. PC Buses [descriptions and pin outs].
The IBM PC uses a different pinout for the mouse interface.
The standard: The Apple Desktop Bus specification, revision F.
Version F was the last standard to be released, with no further updates.





Peripheral Manufacturers

Mouse & Keyboard Manufacturers
Most of which will be either USB or wireless connections.

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Modified 3/03/12
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