Adaptec 3940UW User's Guide download pdf (Page 34)

2-14

AHA-3940U/3940UW/3940UWD User’s Guide

Stock Number: 511041-00, Rev. B Page: 2-14

Print Spec Number: 494569-00

Current Date: 2/14/97 ECN Date: 2/17/97

Note:

Do not set a channel’s termination to Disable if there is

no device on that SCSI bus. It may hang the system.

SCSI IDs

Each device on the SCSI bus, including the host adapter, must have a

unique SCSI ID. The SCSI ID serves two purposes:

■

It uniquely defines each SCSI device on the bus.

■

It determines which device controls the bus when two or more

devices try to use it at the same time.

SCSI IDs on one channel do not interfere with the IDs on another

channel. This applies to two SCSI host adapters that implement dif-

ferent buses as well as dual channels on a single host adapter.

SCSI ID Priority

On an 8-bit SCSI bus, SCSI ID 7 has the highest priority, and SCSI ID

0 has the lowest priority. From highest to lowest, the complete order

is: 7, 6, 5, 4, 3, 2, 1, 0.

On a 16-bit SCSI bus, the priority scheme goes from SCSI ID 7 (the

highest priority) to SCSI ID 0, and then from SCSI ID 15 to SCSI ID 8,

so that SCSI ID 8 is the very lowest priority. From highest to lowest,

the complete order is: 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8.

Figure 2-14. Host Adapter Termination on SCSI Channel B (AHA-3940U/3940UW)

Termination

Host Adapter

Termination

Enabled

Automatically

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Adaptec 3940UW User's Guide Page 34