Advantech PCA-6185 Terminating the SCSI bus, Configuring the SCSI interface with SCSISelect

7.4 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 device at the end of the each cable, or the end of the cable itself, has a terminator installed (or enabled). Terminators must be removed, or termination must be disabled, on devices between the ends of each cable.

Since the method for terminating a SCSI device can vary widely, refer to the device’s documentation for instructions on how to enable or disable termination. Here are some general guidelines for termination:

•Internal Ultra 320 and Ultra 2 SCSI devices come from the factory with termination disabled and cannot be changed. Proper termination for internal Ultra 320 and Ultra2 SCSI devices is provided by a 68-pin Internal LVD (low voltage differential) SCSI cable, which has a built- in terminator at its end.

•Termination on non-Ultra 320 and Ultra2 internal SCSI devices usually is controlled by manually setting a jumper or a switch on the device, or by physically removing or installing one or more resistor modules on the device.

•Termination on most external SCSI devices is controlled by installing or removing a SCSI terminator. However, termination on some exter- nal SCSI devices is enable or disabled by setting a swetich on the back of the SCSI device.

•The last external Ultra 320 or Ultra2 SCSI device must be terminated with an LVD/SE (low voltage differential/single ended) terminator plug to ensure that the device will operate at its maximum speed. If you use a different kind of terminator plug, the data I/O rate will decrease.

By default, termination on the SCSI controller itself is set to Automatic (the preferred method). We recommend that you do not change this default setting.

7.5 Configuring the SCSI interface with SCSISelect

SCSISelect, included with the CPU card, enables you to change SCSI set- tings without opening the computer. SCSISelect also enables you to low- level format or verify the disk media of your SCSI hard disk drives. The following table lists the available and default settings for each SCSISelect option.

Note: The default settings are appropriate for most sys-

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