Apple 250 manual Hard Disk Interface, Interface Requirements

C H A P T E R 2

Hardware Modifications

Hard Disk Interface

This section describes the interface requirements for the 200 MB hard disk drive. It provides specifications and signal assignments for the SCSI connector.

Note

The interface requirements for the 120 MB hard disk drive are described in Chapter 3 of the Macintosh Developer Notes, Number 2, Macintosh Duo System. ◆

Interface Requirements

The interface to the hard disk is an ANSC X3T9.2 SCSI interface. It implements the Apple SCSI command protocol and diagnostic command set. The buffer size supports a 1:1 interleave. The drive supports the SCSI asynchronous information transfer. The transfer rate is 1.5 MB per second (minimum). An embedded controller provides error recovery algorithms, which include error check and correction (ECC), seek retry, head offset (for open-loop systems), and defect management. The SCSI interface provides hardware-detectable SCSI ID.

SCSI Connectors

The 200 MB disk drive SCSI connector comprises two segments, as shown in Figure 2-3. The first segment has 40 pins, arranged in two rows. It transfers SCSI signals between the CPU and the hard disk drive, and it also supplies power to the drive. The second segment of the connector accommodates the SCSI ID.

Figure 2-3	200 MB hard drive SCSI connector
		SCSI commands and power			SCSI ID
Pin 39			Pin 1	Pin 7		Pin 1

Pin 40 Pin 2

Pin 8 Pin 2

Key

200 MB Hard Disk Drive 11