Technical information

CHAPTER 1

Introduction

How the DOS Compatibility Card Works

I/O Capabilities 1

The DOS Compatibility Card uses I/O devices built into or connected to the Macintosh

host computer. This section describes the I/O capabilities; for more information on their

operation, see “I/O System” in Chapter 2.

Floppy Disk 1

The DOS Compatibility Card has access to the Macintosh host computer’s 3.5-inch

internal ﬂoppy drive. The drive can read and write DOS-formatted ﬂoppy disks. I/O

data transfers use the DMA channel when RAM SIMM is installed on the card. When

using shared memory, I/O data transfers are handled by the disk drivers in the

Macintosh Operating System (Mac OS).

Hard Disk 1

The DOS Compatibility Card has access to the host computer’s internal hard drive and

other SCSI devices. I/O data transfers use the DMA channel when RAM SIMM is

installed on the card. When using shared memory, I/O data transfers are handled by the

disk drivers in the Mac OS.

Serial Ports 1

The DOS Compatibility Card has access to the serial ports on the Macintosh host

computer. To provide software compatibility, an IC on the card emulates the registers of

the standard serial port ICs found in most PC/AT computers. For more information on

An adapter cable is necessary to connect a PC serial device to a Macintosh serial port.

Table 1-2 shows the signals on the 8-pin connector on the Macintosh serial ports and the

corresponding connections on the 25-pin connector used with a PC serial port.

Table 1-2

Corresponding serial-port signals

Pin number

on the

Macintosh port

RS-422

signal name

Pin number

on the PC port

RS-232

signal name

1 HSKo 20 DTR

2 HSKi 5, 8 CTS, DCD

3 TXD– 2 TXD

4 GND 7 GND

5 RXD– 3 RXD

6 TXD+ n. c. none

7 GPi n. c. none

8 RXD+ 7 GND