Technical information

CHAPTER 1

Introduction

How the DOS Compatibility Card Works

Note

The serial ports on some Macintosh models have 9-pin sockets.

Those sockets accept either 9-pin or 8-pin connectors.

◆

The Macintosh serial ports are RS-422 ports and do not support all the RS-232 signals. In

particular, the Carrier Detect (CD), Data Set Ready (DSR), Request To Send (RTS), and

Ring Indicator (RI) signals are not available. Not all RS-232 devices will work using the

RS-422 protocol.

Parallel Printer Port 1

A custom IC on the DOS Compatibility Card emulates a compatible parallel port

interface and enables the driver software to send printer data to a printer through the

Macintosh host computer. The printer may be connected directly to the Macintosh

computer’s serial port or it may be on a network and selected by means of the Chooser.

The IC provides register compatibility only; for more information, see “Printer Port

Support” on page 28.

Keyboard and Mouse 1

The DOS Compatibility Card includes hardware that emulates a PC keyboard and

mouse using inputs from the keyboard and mouse on the Macintosh host computer. The

software protocols for the keyboard and mouse are the same as on a standard PC.

Note

The DOS Compatibility Card can work with another user input device,

such as a trackball, but the device must be connected to the Macintosh

host computer by way of the ADB port.

◆

The user can deﬁne a key combination to switch operation of the user interface

devices (the keyboard, the mouse, and the monitor, if shared) between the card and

the Macintosh host computer. The key combination consists of at least one modiﬁer

key and another key. For information about setting the key, see Chapter 2 in the

user’s manual.

Sound 1

The DOS Compatibility Card contains audio mixing circuitry that enables it to mix PC

sound output with the CD sound output of the Macintosh host computer. A ribbon cable

carries the CD sound signal from the host computer to the card. Another

ribbon cable carries the mixed sound back to the host computer where it is mixed

with the computer’s sound output and sent to the internal speaker and the sound

output jack.

Sound is generated on the DOS Compatibility Card by either the 8254 interval timer

(square wave output) or the sound expansion card. The interval timer is responsible

for the standard system beep and sound effects. The sound expansion card provides

16-bit stereo sound output only and is software compatible with the Sound Blaster