Scsi Bus - Seagate ST11200 Product Manual

6
_____________________________________________________________________________________
2.0

SCSI bus

This manual discusses only the "logical" and timing characteristics of the SCSI system and interface. The
SCSI bus physical characteristics (voltages, connector configurations, pinouts, etc.) are given in the indi-
vidual disc drive Product Manuals (Volume 1) Section "Interface requirements", which covers all of the inter-
face requirements and SCSI features supported by the drive described in the particular Product Manual
being referenced.
Communication on the SCSI Bus is allowed between only two SCSI devices at a time. Some Seagate drives
support systems with a maximum of eight SCSI devices including the host computer(s) connected to the
SCSI bus. Some Seagate drives support systems with a maximum of sixteen SCSI devices on the SCSI bus.
Each SCSI device has a SCSI ID Bit assigned as shown in Figure 2.0-1. The SCSI ID is assigned by installing
from 0 to 3 (8 device systems) jumper plugs or 0-4 (16 device systems) 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 disc drive
Product Manual, Section "Option/configuration headers".
When two SCSI devices communicate on the SCSI Bus one acts as an initiator and the other acts as a target.
The initiator (typically a host computer) originates an operation and the target performs the operation. The
disc drive always operates as a target, unless specified otherwise (i.e., certain commands are supported) in
the individual drive Product Manual.
DB(7) DB(6)
SCSI ID = 6
SCSI ID = 7
Additional SCSI ID bits for devices that support 16 devices on the SCSI bus.
DB(15) DB(14)
SCSI ID = 14
SCSI ID = 15
Figure 2.0-1. SCSI ID bits
Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
DB(5) DB(4)
SCSI ID = 4
SCSI ID = 5
DB(13) DB(12)
SCSI ID = 12
SCSI ID = 13
DB(3) DB(2)
SCSI ID = 2
SCSI ID = 3
DB(11) DB(10)
SCSI ID = 10
SCSI ID = 11
DB(1) DB(0) DATA BUS
SCSI ID = 0
SCSI ID = 1
DB(9) DB(8) DATA BUS
SCSI ID = 8
SCSI ID = 9