Apple Desktop Bus, ADB Pinout and Signal Assignments

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].

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 The ADB bus is OBSOLETE and was replaced by the Firewire bus.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 Macintoshes 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 Macintoshes do not have soft-power capabilities; on these machines, grounding pin 2 will have no effect.

**ADB Mouse Pin Out**
Pin Number	Pin Function
1	Data
2	Power up
3	5 volt
4	Ground

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.

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.
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Peripheral Manufacturers

Mouse & Keyboard Manufacturers
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Engineering Key words: Apple, Macintosh, MAC, Computer Buses, Connector Pin-Outs, Interface Standard, Specification, Spec,
Physical Interface, Description, Personal Computer Interface, Peripheral, Printer Interface, Keyboard, Obsolete, Out-dated, Legacy Equipment, Gear.


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