Specifications

CHAPTER 2
Architecture
18 Block Diagram and Main ICs
the PCI bus architecture. It provides power management control functions for Energy
Star–compliant features included in the Macintosh Performa 6400 computer. The O’Hare
IC is connected to the PCI bus and uses the 33 MHz PCI bus clock.
The O’Hare IC includes circuitry equivalent to the IDE, SCC, SCSI, sound, SWIM3, and
VIA controller ICs. The functional blocks in the O’Hare IC include the following:
■ support for descriptor-based DMA for I/O devices
■ system-wide interrupt handling
■ a SWIM3 floppy drive controller
■ SCSI controller (MESH based)
■ SCC serial I/O controller
■ IDE hard disk interface controller
■ sound control logic and buffers
The O’Hare IC provides bus interfaces for the following I/O devices:
■ Cuda ADB controller IC (VIA1 and VIA2 registers)
■ AWACS sound input and output IC
■ 8 KB non volatile RAM control
The SCSI controller in the O’Hare IC is a MESH controller. DMA channels in the O’Hare
IC are used to support data transfers. In the Macintosh Performa 6400 computer, the
clock signal to the SCSI controller is 45 MHz.
The O’Hare IC also contains the sound control logic and the sound input and output
buffers. There are two DMA data buffers—one for sound input and one for sound
output—so the computer can record sound input and process sound output
simultaneously. The data buffer contains interleaved right and left channel data for
support of stereo sound.
The SCC circuitry in the O’Hare IC is an 8-bit device. The PCLK signal to the SCC is an
24.5 MHz clock. The SCC circuitry supports GeoPort and LocalTalk protocols.
AWACS Sound IC 2
The audio waveform amplifier and converter (AWACS) is a custom IC that combines a
waveform amplifier with a 16-bit digital sound encoder and decoder (codec). It conforms
to the IT&T ASCO 2300 Audio-Stereo Codec Specification and furnishes high-quality sound
input and output. For information about the operation of the AWACS IC, see Chapter 3
of Developer Note: Power Macintosh Computers, available on the developer CD-ROM and
as part of Macintosh Developer Note Number 8.
Cuda IC 2
The Cuda IC is a custom version of the Motorola MC68HC05 microcontroller. It provides
several system functions, including