Specifications

8
Cables and termination
Please refer to the documentation for your SCSI
devices to determine they are Wide or Narrow,
UltraWIDE SCSI, Ultra2 SCSI, Ultra3 or Ultra
320.
3 Determine which terminator to use
Use an LVD terminator if you are only using LVD
devices.
Although you can use a Single-Ended
terminator, all devices will be limited to Ultra
SCSI speeds. Single-Ended devices require a
Single-Ended terminator. If you use an LVD
terminator with Single-Ended devices, the system
may hang or devices may not be seen on the SCSI
bus. Some termination manufacturers provide
automatically sensing terminators.
External terminators should be attached to the
last external device in the SCSI chain.
Don’t use
any other termination on the external SCSI chain.
The last device on an internal SCSI chain should
also be terminated. This can be done in several
ways. Many Single-Ended Ultra SCSI and earlier
devices provide a jumper setting for applying
termination: place a jumper over the pins
designated for termination on the last device on
the internal cable. Check with your drive
manufacturer if you are not sure which pins to use.
LVD Ultra2 and Ultra3 SCSI devices cannot
supply their own termination.
Use an internal
ribbon cable which has a SCSI terminator
attached to the end of it, connect the unterminated
end of the cable to the host adapter card and the
internal drives to the subsequent connectors. The
terminator should be at the opposite end of the
cable from the host adapter card.
Wide (16-bit) and Narrow (8-bit) devices can be
connected together on the same connector of the
host adapter card, but wide devices must be
attached first, followed by narrow devices.
To
terminate the SCSI bus, the cable or adapter used
to convert from a wide (68-pin) connector to a
narrow (50-pin) connector provides partial
termination, allowing upper 8-bits (or byte) of the
wide SCSI bus to be properly terminated. A
narrow terminator should be used on the last
narrow device to terminate the rest of the SCSI
bus. A SCSI bus without partial termination
between the wide and narrow devices may at first
appear to work correctly, but occasional I/O errors
will occur without proper termination.
If you use both internal and external connectors
and mix Single-Ended and LVD devices on the
same bus, even if using different connectors, the
host adapter card will operate with Single-Ended
signaling at UltraSCSI speeds.
Automatic termination:
when both internal and
external connectors are used, the host adapter card
detects the presence of devices and turns off
termination. If devices are removed from one
connector of the card, the host adapter will
automatically detect the change, and enable its
own termination.
Software controlled termination: You may have
to override the host adapter’s automatic
termination if only narrow devices are attached to
one connector and wide devices are attached to
the other connector on the same bus. The host
adapter must supply partial termination to the
upper 8-bits (byte), but it will not do so
automatically. Please refer to your ExpressPCI
Utilities manual for instructions on setting the
host adapter’s termination to Upper Byte.
Termination power: host adapters supply
termination power to the bus at all times and many
SCSI devices are also able to supply termination
power. SCSI signal quality, particularly with long
or marginal quality cables, may be improved if the
device supplies the termination power. Contact
your device manufacturer for more information
on your device’s ability to supply termination
power.