Terminating The Scsi Bus; Terminating Scsi Devices; Terminating The Host Adapter - Adaptec AHA-3940 User Manual

Terminating the SCSI Bus

SCSI termination must be enabled on the first and last physical
devices on SCSI Channels A and B of your AHA-3940/3940W host
adapter; otherwise, the devices will not operate properly. You may
need to change the termination setting on some SCSI devices when
you install them. In general, the procedure for terminating the SCSI
bus is as follows:
1
Determine which two SCSI devices (including the host
adapter) are at the two ends of the SCSI channel (SCSI bus).
Then terminate these devices, if they are not already
terminated.
2
Disable termination on all other devices on the SCSI bus, if it is
not already disabled.

Terminating SCSI Devices

Most SCSI disk drives, CD-ROM drives, and other peripheral
devices have a jumper or a switch close to the SCSI connector to con-
trol SCSI termination. Some SCSI devices have resistor modules that
you can remove or insert to change the termination setting.
Terminate the SCSI device at the end of the internal or external SCSI
cable, and disable termination on all other devices on the SCSI bus.
Read the device documentation if you are not sure how to enable or
disable termination on your SCSI devices.
Note:
Some SCSI disk drives allow termination power to be
supplied to their resistor modules from the SCSI bus instead
of from the drive's power supply. AHA-3940/3940W host
adapters support this option, because they always supply
termination power on the SCSI bus.

Terminating the Host Adapter

Termination for Channels A and B is Enabled by default on
AHA-3940/3940W host adapters. You can change this setting, if nec-
essary, with the SCSISelect configuration utility, as described in
Chapter 3, Configuring Your Host Adapter.
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AHA-3940/3940W User's Guide
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Installing Your Host Adapter and SCSI Devices
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ECN Date: 08/30/94
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