Specifications

CHAPTER 1
Introduction
ADB Ports 15
ADB Ports 1
The ADB ports are functionally the same as those on other Macintosh computers.
The Apple Desktop Bus 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 Macintosh LC 520 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 controller to the outside world. Table 1-5 lists the ADB
connector pin assignments. For more information about the ADB, see Guide to the
Macintosh Family Hardware, second edition.
Note
The total current available for all devices connected to the +5V pins on
the ADB and the modem port is 500 mA. Each device should use no
more than 100 mA. ◆
Sound 1
Like other Macintosh computers, the Macintosh LC 520 computer can create sounds
digitally and play the sounds through its internal stereo speakers or send the
sound signals out through the sound out connectors. For recording sound, the
Macintosh LC 520 computer has a built-in microphone as well as an external sound input
jack.
The sound system includes a playthrough feature that allows an external audio source
to be mixed with computer-generated sound and played through the speakers or the
sound out connector. For more information, see the section “Sound Modes” beginning on
page 22.
Table 1-5 ADB connector pin assignments
Pin
number 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. A 1-ampere fuse at the output
satisfies safety requirements.
4 GND Ground from the computer.