Adaptec 2930U2 User Reference - Page 9

Terminating the SCSI Bus - ultra2

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Understanding SCSI Terminating the SCSI Bus To ensure reliable communication on the SCSI bus, the ends of the SCSI bus must be properly terminated. This is accomplished when the peripheral at the end of each cable, or the end of the cable itself, has a terminator installed (or enabled). The peripherals between the ends of each cable must have its terminator removed (or disabled). Since the method for terminating a SCSI peripheral can vary widely, refer to the peripheral's documentation for instructions on how to enable or disable termination. Here are some general guidelines for termination: s Termination on internal SCSI peripherals usually is controlled by manually setting a jumper or a switch on the peripheral, or by physically removing or installing one or more resistor modules on the peripheral. s Termination on external SCSI peripherals usually is controlled by installing or removing a SCSI terminator. On some external peripherals, termination is controlled by setting a switch on the back of the drive. s By default, termination on the SCSI Card 2930U2 itself is automatic (the preferred method). To manually set termination on the SCSI Card 2930U2, see Configuring the SCSI Card 2930U2 with SCSISelect on page 15. s Internal Ultra2 peripherals (such as low voltage differential (LVD) hard disk drives) are set at the factory with termination disabled and cannot be changed. Proper termination for internal Ultra2 peripherals is provided by the built-in terminator at the end of the Ultra2 internal SCSI cable. s Most non Ultra2 SCSI peripherals come from the factory with termination enabled. 3

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3
Understanding SCSI
Terminating the SCSI Bus
To ensure reliable communication on the SCSI bus, the ends of the
SCSI bus must be properly terminated. This is accomplished when
the peripheral at the end of each cable, or the end of the cable itself,
has a terminator installed (or enabled). The peripherals between the
ends of each cable must have its terminator removed (or disabled).
Since the method for terminating a SCSI peripheral can vary widely,
refer to the peripheral’s documentation for instructions on how to
enable or disable termination. Here are some general guidelines for
termination:
■
Termination on internal SCSI peripherals usually is controlled
by manually setting a jumper or a switch on the peripheral, or
by physically removing or installing one or more resistor mod-
ules on the peripheral.
■
Termination on external SCSI peripherals usually is controlled
by installing or removing a SCSI terminator. On some external
peripherals, termination is controlled by setting a switch on the
back of the drive.
■
By default, termination on the SCSI Card 2930U2 itself is auto-
matic (the preferred method). To manually set termination on
the SCSI Card 2930U2, see
Configuring the SCSI Card 2930U2
with SCSISelect
on page 15.
■
Internal Ultra2 peripherals (such as low voltage differential
(LVD) hard disk drives) are set at the factory with termination
disabled and cannot be changed. Proper termination for inter-
nal Ultra2 peripherals is provided by the built-in terminator at
the end of the Ultra2 internal SCSI cable.
■
Most non Ultra2 SCSI peripherals come from the factory with
termination enabled.