Specifications

CHAPTER 2
Hardware Design
26 I/O System
I/O System 2
The interface between the Macintosh computer and the 12” and 7” cards is provided by
the PCI connector, which connects the PCI bus on the PC system with the PCI bus on the
Macintosh side. I/O control on the cards is provided by the Mustard ASIC and the 8242
controller, which controls the mouse and keyboard. The Mustard ASIC acts as a bridge
between the two PCI buses. The ASIC also contains PC I/O emulation logic, which
integrates many of the I/O functions required to support the PC. It supports the
following features:
■ emulation of two 16C450-compatible serial ports
■ emulation of one Centronics parallel printer port
■ emulation of keyboard and mouse controller that allows the cards to access the
Macintosh keyboard and mouse by means of the ADB
■ a 64-bit message mailbox with a 32-bit command port
■ address translation
■ power-on reset logic
■ general-purpose I/O ports (autoconfiguration logic)
■ interrupt status and mask registers
The Mustard ASIC can function either as a slave or as an alternate bus master on the
Apple PCI bus or on the PC PCI bus.
Serial Port Support 2
From the PC environment, you can connect a modem or other serial device to the
Macintosh serial port. This is an 8-pin serial connection on the computer’s back panel,
identified by either a printer or modem icon.
To support serial ports, the Mustard ASIC contains two identical sets of UART emulation
registers. These registers emulate the hardware of the standard 16C450 serial port ICs
found in many PC/AT computers. When the microprocessor on the 12” or the 7” card
accesses these registers, interrupts are generated in the Macintosh host computer. These
interrupts signal a driver on the Macintosh computer to route the data to the Macintosh
serial ports.
The Macintosh serial ports are RS-422 ports and do not support the following RS-232
signals: Carrier Detect (CD), Data Set Ready (DSR), Request to Send (RTS), and Ring
Indicator (RI) signals.
An adapter cable is needed to connect a PC serial device to a Macintosh serial port. To
help you design a custom cable to make the serial connection, Table 2-5 shows the signal
names and pin numbers on the RS-422 8-pin connector on the Macintosh serial port, the