Roland DM-80 Owner's Manual page 38

EXTERNAL SCSI TERMINATION
About SCSI termination !
The standard SCSI specification requires that both ends of a SCSI buss or chain must
-be properly "terminated". This involves adding a set of resistors across each SCSI
data line which are fed from 5 VDC. The DM ~ 80 itself represents the beginning
of the SCSI chain. It is properly terminated inside the unit. If however, you add additional
drives externally they must be terminated correctly as well. But remember, only the
last drive on the chain is to be terminated. e.g. If you have a 300 Meg External drive
and a 600 Meg external drive connected to the "SCSI A" port on the DM ~— 80, the
last drive on the cable must be terminated.
Most drives are available with internal or external terminators.
Internal terminators are usually small in line resistor packs called "SIPS". They plug
directly into sockets on the main controller circuit board of the drive itself.
External terminators are usually rectangular boxes which can be attached to a separate
50 pin Centronix connector on the rear panel of the drive. Other external terminators
have a 50 pin connector on both sides so the terminator can be plugged on the drive
and the cable from the DM-— 80 can be plugged into the terminator.
BE "CAREFUL OF ..4.20.
DOUBLE TERMINATION :
Be sure that the last drive in the Chain is not double terminated. That means that
it has internal terminator resistors installed as well as an external 50 pin terminator.
You must remove either the internal SIPS or the external terminator package.
NO TERMINATION :
Be sure to check that the last drive is terminated either internally or externally, and
that it is terminated correctly.
TERMINATOR POWER :
SCSI terminators MUST be provided with 5 VDC power in order to operate correctly.
The DM -~80 DOES NOT provide this terminator power for external devices. The power
must come from the device itself. Some drives give a switch option to allow for the
drive to provide power to the terminator. You must be sure that the drive is providing
power to the terminator.
We have seen many customers who have added external terminators to their drives
but the drives did not provide power. THIS IS WORSE than NO terminator at all. The
DM — 80 seems to exhibit many SCSI errors and can exhibit random "lock ups" and
other problems if an Unpowered Terminator has been installed on an external device.
Most drives provide power to the terminator resistors if you sue the SIPS packs directly
on the circuit board. However, many drive housings do not provide terminator power
to the rear connector.