Configuring HP-UX For Peripherals

Chapter 3 93
Configuring Interface Cards
Selecting Device Drivers for Your Interface Cards
All devices must be connected to a common (single point) system
reference ground. The system ground must be isolated from other
electrical devices such as copying machines, arc welders and air
conditioners. Cables supplied by HP have correct grounding.
SCSI Signal Termination
To successfully transmit signals, the SCSI bus requires that both ends of
the bus be terminated. This statement means that the last device on the
bus, no matter what type of device it is (disk, tape, or interface card),
must have a terminator installed on its second SCSI connector. The
terminator is (or acts as) a small resistor that provides matching
impedance on the bus circuit. Without such termination, data traveling
on the bus is likely to be corrupted and the protocol upset to the point
that it hangs the bus.
Some devices (particularly host adapters) contain internal SCSI bus
terminators or require special terminators. If two devices supply
termination power, locate them at each end of the SCSI bus. Refer to the
specific hardware manuals of host adapters and the devices on the bus
for instructions on how to prevent excessive or improper SCSI bus
termination.
CAUTION Only the two ends of a SCSI bus should be terminated. Excessive or
improper termination overloads the SCSI port's termination power
(TERMPWR) circuitry. Overloading can result in blowing the
TERMPWR fuse on the adapter, or damaging transceivers on any
attached device, including the adapter.
All HP SCSI products are shipped with appropriate terminators. Table
3-15, “SCSI Terminators,” should be helpful if you need to order
HP device #4 none 0.4m 3.9m
Total 3.9m
Table 3-14 Example of SCSI Cable Length Calculation
Starting Point
Device Cable to Next Device
Internal
Cable
Cumulative
Cable Length