9 ATTO Technology ExpressPCI Ultra/WIDE SCSI Host Adapters Installation and Operation Manual
To set up cabling and termination:
1
Determine whether your ATTO Express PCI
adapter is a single channel or dual channel
model. One external connector indicates a
single channel host adapter; two external
connectors indicate a dual channel host
adapter.
2
Determine if SCSI devices will be installed
internally or externally.
Total bus cable length,
varies by host adapter and
type of attached devices. Refer to Exhibit 3.1-1
for details on maximum cable length.
If you combine Wide 16-bit and Narrow 8-bit
devices on the same connector,
connect the
Wide devices first (closest to the connector).
Exhibit 3.1-4
Please refer to the documentation for
your SCSI devices to determine they are Wide or Narrow.
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.
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.
NOTE 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 to set the host adapter’s
termination to Upper Byte.
Internal
Connection
External
Connection
Termination
Selection
Wide Device
Wide Device
None
not used
Wide Device
Full
Wide Device
not used
Full
Narrow Device
not used
Full
not used
Narrow Device
Full
Narrow Device
Wide Device
Upper
Wide Device
Narrow Device
Upper
Narrow Device
Narrow Device
Upper
