Terminating The Scsi Bus; Internal And External Scsi Devices - Adaptec AVA-2822 User Manual

Terminating the SCSI Bus

To reduce signal reflections on the SCSI bus, the first and last physi-
cal SCSI devices (including the host adapter) must have a set of
resistors called terminators either installed or enabled.
Identify which two SCSI devices form the physical endpoints of
your SCSI bus, then terminate these devices. All other SCSI devices
installed between the ends of the SCSI bus must have their termina-
tors either removed or disabled.
Some SCSI devices use a jumper or a switch located close to their
SCSI connector(s) to control termination. On other SCSI devices, you
must physically remove or install resistor module(s). Refer to the
device's documentation to determine how to enable or disable ter-
mination on your particular SCSI device.
Note:
Since the AVA-2820/2822/2825 always supplies termi-
nation power to the SCSI bus, disable SCSI devices from
supplying termination power. See your device's documenta-
tion for details.
The AVA-2820/2822/2825 termination is software selectable and is
Enabled by default. Host adapter termination must be disabled only
if the host adapter is located in the middle of the SCSI bus. Refer to
Host Adapter SCSI Termination on page 3-6 to disable host adapter
termination.
Note the recommended termination possibilities listed in the subsec-
tions below.

Internal and External SCSI Devices

If both internal and external SCSI devices are connected to the host
adapter, the last external SCSI device and the last internal SCSI
device must be terminated. Since the host adapter is situated in the
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