Seagate Ultra 320 User Manual download pdf (Page 27)

Parallel SCSI Interface Product Manual, Rev. A ) 13

2.0 SCSI bus

This manual discusses only the “logical” and timing characteristics of the SCSI system and interface. A general

description of the SCSI bus physical characteristics (voltages, connector configurations, pinouts, etc.) are

given in the individual drive’s Product Manual, in the “Interface requirements” section, which covers the inter

face requirements and SCSI features supported by the drive described in the particular Product Manual being

referenced. For all of the physical details of the SCSI interface, consult the ANSI standards referenced in Sec

tion 1.1.2.

Communication on the SCSI Bus is allowed between only two SCSI devices at a time. Seagate drives support

systems with a maximum of 16 SCSI devices including the host computer(s) connected to the SCSI bus. Each

SCSI device has a SCSI ID bit assigned as shown in Table

1. The SCSI ID is assigned by installing 0-3 jumper

plugs onto a connector in a binary coded configuration during system configuration. Some drive models have

an interface that includes the SCSI bus ID lines, so that the host can set the drive ID over the interface (see

individual drive’s Product Manual, “Option/configuration headers” section).

When two SCSI devices communicate on the SCSI Bus, one acts as a SCSI initiator port and the other acts as

a SCSI target port. The initiator (typically a host computer) originates an I/O process and the target performs

whatever operations/tasks are called for by the I/O process. Devices arbitrate to get control of the bus to per

form whatever communications are required by the current I/O process. As part of the arbitration process,

devices on the SCSI bus assert their bus ID (one of the DB lines as shown in Table

1). The arbitration process

is discussed in more detail later. Devices supported by this interface specification always operate as targets,

unless otherwise specified (i.e., if certain commands are supported) in the individual drive’s Product Manual,

Volume 1.

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 185 186

No comments

Seagate Ultra 320 User Manual Page 27