Specifications

CHAPTER 2
Architecture
22 Block Diagram
Combo Custom IC 2
In the Macintosh LC 520 computer, the functions of two interface ICs, the SCC (85C30)
and the SCSI (53C80), are combined into one device, the Combo IC (85C80). The SCSI
port on the Macintosh LC 520 is the same as that on the Macintosh LC III.
The SCC (serial) ports are also like their counterparts except that they include the GPi
signal (on pin 7). The GPi signal can be used for input handshaking or for a receive clock
input to support a synchronous modem. The pin assignments for the serial ports are
listed in Table 1-4 on page 14.
Cuda ADB Controller 2
The Cuda IC is a version of the 68HC05 microcontroller. It provides the ADB interface
and control signals to the DFAC II IC along with parameter RAM, the real-time clock,
and soft-power control. For a description of soft power, see the section “Power On and
Off” beginning on page 6.
Sound Circuits 2
The analog sound processing devices in the Macintosh LC 520 computer are built into a
custom IC called the DFAC II. In addition, the Ardbeg custom IC performs sound routing
and control along with its other digital functions.
For sound input, the DFAC II processes the signal from the internal microphone or the
sound input jack through a sound input amplifier (with automatic gain control), an input
filter, an A/D converter, and the necessary switching circuits.
For sound output, circuits in the Ardbeg custom IC receive data from the sound buffer
and generate a pulse-width-modulated (PWM) signal that is sent to the DFAC II. After
low-pass filtering in the DFAC II, the signal is sent to the sound output jacks and to
separate amplifiers that drive the built-in speakers. Inserting a plug into either sound
output jack disconnects the internal speakers.
Sound Modes 2
The DFAC II is normally used in one of four modes of operation:
■ Sound playback: computer-generated sound is sent to the speaker and the sound
output jack.
■ Sound playback with playthrough: computer sound and sound input are mixed and
sent to the output.
■ Sound record: sound input is recorded; this is the preferred method for recording,
especially when using the built-in microphone.
■ Sound record with playthrough: input sound is recorded and also fed through to
the output.