SCSI Information
In this section we provide a short and hopefully helpful guide concerning correct termination and wiring.
Our customer support experience showed that many problems are caused by an incorrect SCSI termination or installation. Please make absolutely sure that your system is correctly configured and terminated. This especially applies to WIDE or U2W SCSI adapters.
Termination
- A SCSI bus always has to be terminated at both ends.
- If there is both an external and an internal wire, the internal cable has to be terminated at its end as well as the external cable. To do this, activate the termination on the last device or use a special terminator.
- Make sure that no device in the chain may be terminated. This happens for example if the adapter is terminated and a device is attached to the external slot connector.
- If you use a WIDE adapter that has its wide (16 bit) bus connected to a narrow (8 bit) external port you have to make sure that the high order byte of the bus is properly terminated. This can be achieved using the adapter's setup program or, with onboard SCSI adapters, by a special slot adapter.
- However many onboard adapters come with a slot panel that does not provide proper termination of the high order byte of the wide bus. These slots should not be used.
Correct wiring
SCSI devices must be connected using a single wire as a "daisy chain" without any forks. With WIDE adapters providing three internal connectors you have to observe that two of these connectors are connected to the same bus. Using these two connectors at the same time results in a fork that is not allowed and very likely to cause problems.
SCSI cable length
The maximum cable length differs depending on the interface type:
| Number of devices
(incl. Adapter) |
SCSI-1 | SCSI-2 | Ultra(W)-SCSI | U2W-SCSI |
|---|---|---|---|---|
| 1-4 devices | 6 meter | 3 meter | 3 meter | 12 meter |
| 5-7 devices | 3 meter | 3 meter | 1 meter | 12 meter |
If both external and internal devices are used, the lengths of both cables have to be added.
Please make sure that there is a minimum cable length of 30 cm (approximately 7.5") between each device.