Specifications
Page A-3SCSI Termination
2.For AM-1001 subsystem installations, the last SCSI device attached to the
connector farthest down the cable away from the host computer must have its
terminators installed. All SCSI devices inside the host computer must have their
terminators removed. If you are mixing SCSI-1 and SCSI-2 disk drives, do not
terminate the last SCSI device in the subsystem; instead, plug an external
terminator (PRA-00222-00) into the open rear panel SCSI connector on the rear
panel of the AM-1001 subsystem. This will properly terminate all SCSI-1 and
SCSI-2 devices in both the host computer and the subsystem.
A.2TERMINATION POWER
In order to properly control SCSI bus termination, a termination power source must be
provided; this is especially important when using an external terminator.
Why is Termination Power so important when using an external terminator?
In order for terminators to do their job, they must have a power source. In most (but not
all) cases, a SCSI peripheral will supply termination power to its own on-board
terminators, even if the SCSI host controller or no other SCSI peripheral is supplying
termination power to the SCSI bus. However, for an external terminator to be effective
there has to be termination power supplied to the SCSI bus. If no termination power is
available, the external terminator is not going to do its job, which means your SCSI bus
is not terminated. This may result in a computer that either won’t boot or once booted
may tend to hang frequently. Because SCSI-2 devices transfer data at a higher rate,
they are more prone to display problems when improperly terminated.
SCSI-2 Bus Termination Power Guidelines
Use these guidelines for supplying termination power for your Roadrunner enhanced
computers:
1.AMOS based computers with SCSI-2 implementation will be configured with the
Roadrunner board supplying termination power to the SCSI bus.
2.When the SCSI host controller is supplying termination power, you want your
internally mounted SCSI peripherals to be configured so they do not supply
termination power.
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.
For information on how to configure terminator power on SCSI hard disk and magnetic
tape peripherals, see the following documents:
PDI-00172-10, Rev. A03