Alpha Microsystems Eagle 100 Specifications download pdf (Page 69)

Page A-4 Appendix A

3.If a computer with one or more SCSI peripherals is cabled to a subsystem with

additional SCSI devices, the SCSI devices in the subsystem should be configured

so they do not supply termination power. Ideally, you want the SCSI host

controller in the main system to be the sole source of termination power.

The termination power guidelines described above are valid even when you are using

SCSI peripherals that do not support SCSI-2 protocol.

The SCSI host controller on AM-190 and AM-540 boards is permanently configured to

supply termination power to the SCSI bus. On Roadrunner boards, the termination

power feature can be enabled or disabled by setting a jumper. As of 07/26/94, Alpha

Micro began configuring all Roadrunner boards with termination power enabled. See the

Roadrunner installation instructions for information on how to configure the termination

power jumper.

SASI Bus Termination Power Guidelines

Use the following guidelines to determine which peripheral will be used to supply

termination power for the 50-pin SASI bus:

1.Whenever possible, only one SCSI peripheral will be configured to supply

termination power to the SASI bus.

2.If a computer has more than one SCSI peripheral and at least one of those

peripherals is a disk drive, one disk drive will be configured to supply termination

power to the bus. The other disk or tape SCSI devices will be configured so they

do not supply termination power.

3.If a computer does not have a SCSI disk drive, but does have one or more SCSI

magnetic tape or CD-ROM drives, then one of these devices will be configured to

supply termination power.

4.If a computer with one or more SCSI peripherals is cabled to a subsystem with

additional SCSI devices, one SCSI device in the host computer would normally be

configured to supply termination power for the bus.

You should avoid having a SCSI device in both the host computer and the

subsystem configured to supply termination power. Ideally, you want the source of

the termination power for the bus to be supplied by one power source.

PDI-00172-60, Rev. A02

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Alpha Microsystems Eagle 100 Specifications Page 69