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ADB Port

The Power Macintosh G3 computer has an Apple Desktop Bus (ADB) port for ADB devices and ColorSync control of Apple monitors. The ADB port is functionally the same as on other Macintosh computers. The connector is located on the back of the computer.

The ADB connector is a 4-pin mini-DIN connector. Figure 3-1 shows the arrangement of the pins on the ADB connector.

Figure 3-1 ADB connector

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. For more information about the ADB, see Guide to the Macintosh Family Hardware, second edition.

Table 3-1 ADB connector pin assignments

Pin number



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


The total current available for all devices connected to the +5 V pins on the ADB is 100 mA.

1998 Apple Computer, Inc. — (Last Updated 5 Jan 99)

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