Specifications

CHAPTER 1

Introduction

10 PDS Expansion Slot

PDS Expansion Slot 1

The Macintosh LC 520 computer has a single internal 114-pin expansion connector that

provides direct access to the MC68030 microprocessor from an optional expansion card.

The connector can accept a 96-pin expansion card similar to the PDS card for the

Macintosh Color Classic. Like the PDS connector on the Macintosh LC III, it can also

accept an expansion card that uses all 114 pins to make better use of the power of the

MC68030 microprocessor. Chapter 3, “Expansion,” describes the signals on the PDS

connector and gives guidelines for designing a PDS card for the Macintosh LC 520.

Note

The PDS connector in the Macintosh LC 520 computer accepts the

Apple IIe Card for the Macintosh LC. The internal display provides a

560-by-384-pixel, 16-color display for running Apple IIe software. ◆

SCSI Bus 1

In addition to the internal hard drive and one or more external SCSI devices, the SCSI bus

on the Macintosh LC 520 computer supports the optional internal CD-ROM drive.

SCSI Connectors 1

The internal SCSI connector is a 50-pin connector with the standard SCSI pin

assignments. The external SCSI connector is a 25-pin D-type connector with the

same pin assignments as those in other Apple SCSI devices. Table 1-2 shows the

pin assignments on the internal and external SCSI connectors.

The internal hard disk and optional CD-ROM drive connect to the SCSI bus by means of

connector adapters that allow the drives to slide into their respective mounting bays. For

more information about the internal drives and connector adapters, see Chapter 5,

“Internal Storage Devices.”

SCSI Bus Termination 1

Because the internal portion of the SCSI bus must be long enough to connect multiple

devices, the bus requires termination at both ends. As on other Macintosh models, the

external end of the bus is normally terminated at the last external device. On the

Macintosh LC 520 computer, the internal end of the bus—the end at the last internal hard

disk drive—is terminated in the drive itself.