Specifications

CHAPTER 2
Hardware Design
I/O System 27
pins that carry these signals on PC-style DB9 and DB25 connectors, and the signal names
on the RS-232 connector.
Printer Port Support 2
The Mustard ASIC contains logic that implements all the registers of the standard
Centronics parallel port found on PCs. When the PC accesses these registers, interrupts
are generated in the Macintosh host computer that cause the driver software in the
Mac OS to send data to a print spooler file. The spooler file is then sent to whatever
printer the user selects in the Macintosh environment.
Note
The parallel port interface does not control printer hardware signals and
does not support bidirectional data transfer. ◆
Keyboard and Mouse Controller 2
The Mustard ASIC contains logic that emulates in hardware the PC keyboard and
mouse. It also generates the appropriate serial clock protocol and serial bit stream
required to communicate with the 8242 keyboard/mouse controller. The controller is
configured to support the PS2 mouse, and it makes the protocol identical for both the
mouse and keyboard.
Message Mailbox 2
The message-passing interface in the Mustard ASIC supports simple interrupt-driven
communication between the PC and the Macintosh host computer. The message-passing
interface contains two data registers and one command register. The interface uses a
mechanism of arbitration and grants to control the direction of message transfer. Refer to
Table 2-5 Serial port signals
Macintosh
pin
number
RS-422
signal
name Description
DB9
pin
number
DB25
pin
number
RS-232 signal
name
1 HSKo Handshake signal, output 4 20 DTR
2 HSKi Handshake signal, input 8 5, 8 CTS, DCD
3 TXD- Transmit data inverted 3 2 TXD
4 GND Ground 5 7 GND
5 RXD- Receive data inverted 2 3 RXD
6 TXD+ Transmit data n.c. n.c. —
7 GPi General-purpose input n.c n.c. —
8 RXD+ Receive data 5 7 GND