9 ATTO Technology ExpressPCI Ultra/WIDE SCSI Host Adapters Installation and Operation Manual
jumper placed over the pins designated for
supplying termination. Check with your drive
manufacturer if you are not sure which pins to
use.
LVD Ultra2 and Ultra3 SCSI devices are not
capable of supplying their own termination.
Instead, termination must be supplied by an
outside source, usually an internal ribbon cable
which has a SCSI terminator attached to the end.
Connect the non-terminated 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.
Mixing Wide and Narrow devices
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 in
the chain, followed by Narrow devices. The cable
or adapter used to convert from a wide (68-pin)
connector to a narrow (50-pin) connector must
provide partial termination to allow the upper 8-
bits (or byte) of the Wide SCSI bus to be properly
terminated. A Narrow terminator should then 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 appear to work correctly, but
occasional I/O errors will occur without proper
termination.
Using internal and external connectors on
UL3D/UL3D-66
The UL3D/UL3D-66 has two
connectors on each SCSI bus, an internal
connector and an external connector. Devices can
be attached to both connectors on the same bus.
However, the host adapter card will run with
Single-Ended signaling at UltraSCSI speeds if
Single-Ended and LVD devices are on the same
bus, even if using different connectors.
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 to set 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.
