Seagate Ultra 320 ユーザーズマニュアル
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.
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).
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.
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.