Specifications
Page A-3SCSI Termination
A.1.1Termination Procedure (Without External Terminator)
1.For all AM-1600/1400 computers, the last SCSI device attached to the
connector farthest down the cable away from the CPU board must have its
terminators installed. If only one SCSI device is installed, that device must
be terminated.
2.For 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-2001 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.
The AM-137 board is permanently configured to supply termination power to the SCSI
bus. This will insure power is always available to support an external terminator. It also
means it’s not necessary to reconfigure any of your SCSI peripherals to supply
termination power.
For information on how to configure terminator power on SCSI hard disk and magnetic
tape peripherals, see the following documents:
Each SCSI disk drive shipped by Alpha Micro has a one page notice with
jumper configuration information, including instructions on how to configure
termination power.
PDI-00137-50, Rev. A01