v A termination device for external SCSI devices (if needed to terminate
external SCSI chain). To provide reliable SCSI device operation, use only an
active terminator compatible with the type of devices you are using. For
instance, if you are using all LVD SCSI devices, use an LVD termination
device. If you have any devices on the external SCSI chain that are LVD
devices, you can use both LVD and non-LVD termination devices.
Choosing SCSI cables
Round external SCSI cables vary widely in quality and electrical characteristics.
Be sure that external SCSI cables meet LVD SCSI standards. Do not use cables
shorter than 30 cm (11.8 in.) between any two SCSI devices.
To ensure reliable operation, the total length of the SCSI bus, including both
the internal and external cabling, is an important factor. Follow these
guidelines for total SCSI cable length:
v If any Fast SCSI devices are connected to the SCSI adapter, the total length
of all cables must not exceed 3 meters (9.8 ft.).
v If no Fast SCSI devices are connected, the total length of all cables must not
exceed 6 meters (19.7 ft.).
v If only LVD SCSI devices are connected to the SCSI adapter, the total length
of all cables must not exceed 12 meters (39.4 ft.).
Installing the adapter
Follow these steps to install the SCSI adapter.
Step 1. Assigning SCSI IDs
Each device attached to the SCSI adapter, as well as the adapter itself, must
have a unique SCSI ID number from 0 to 15. The SCSI ID serves two purposes:
it uniquely defines each SCSI device on the SCSI bus, and it determines the
device priority for service on the SCSI bus.
The adapter supports the SCSI configured automatically (SCAM) protocol
which assigns SCSI IDs dynamically and resolves SCSI ID conflicts
automatically at startup. Most SCSI devices currently in use, however, do not
support SCAM. The SCSI IDs on these devices must be set manually. Consider
the following when assigning a SCSI ID:
v Determine the SCSI ID assignments for devices currently installed. You
might be able to use the existing ID assignments. To determine existing SCSI
ID assignments, use one of the following.
– For most IBM computers, press the F1 key during start up after the
memory check completes.
– Use the SCSI utility programs which came with your SCSI devices.
– Inspect the installed SCSI devices to see how the IDs are set.
2-2 IBM PCI Ultra160 SCSI Adapter: User’s Guide
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