ATTO Technology To set up cabling and termination, Wide devices first closest to the connector

last external device in the SCSI chain.

Automatic termination:

To set up cabling and termination:

1Determine 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.

2Determine 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 3.1-1for 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.

Internal	External	Termination
Connection	Connection	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

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

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.

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.

9 ATTO Technology ExpressPCI Ultra/WIDE SCSI Host Adapters Installation and Operation Manual