Advantech 2006957006 5th Edition user manual SCSI terminators

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