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6.5 SCSI terminators
To ensure reliable communication, the SCSI bus must be properly
terminated. Termination is controlled by a set of electrical resistors,
called terminators. Terminators must be placed (or enabled) at the two
extreme ends of the SCSI bus. All devices that lie between the ends
must have their terminators 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 is usually controlled by
manually setting a jumper or switch on the peripheral, or by
physically removing or installing one or more resistor modules on
the peripheral.
• Termination on external SCSI peripherals is usually controlled by
installing or removing a SCSI terminator. On some external
peripherals, termination is controlled by setting a switch on the rear
of the drive.
• By default, termination on the CPU card itself is automatic (the
preferred method).
• Internal Ultra2 peripherals are set at the factory with termination
disabled, which 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.
• Most non-Ultra2 SCSI peripherals come from the factory with
termination enabled.
Chapter 6 SCSI Setup and Configurations
63
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