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Installing the A5150A Adapter
SCSI Bus Termination
Chapter 2 31
In the factory default configuration of the older A5150-60001 HBA, the
pin sets are normally open (not shorted together by the jumper). In the
open state, the A5150A automatically senses whether a cable from a
powered SCSI device is attached, and automatically provides the proper
termination (depending on whether a powered device is present or no
powered device is present).
The HBA senses the presence of connections to powered devices by
detecting the ground signal on pin 50 of the SCSI cable.
• If the HBA detects the ground signal on pin 50 of only the internal or
only the external connector, then termination is automatically
applied on the HBA.
• If the HBA detects the ground signal on pin 50 of both the internal
and external connectors, termination is automatically removed at the
HBA.
• If an A5150A with the auto termination feature enabled is connected
to another device that uses the same method of auto-sensing (for
example, another HBA), the auto termination feature will not work
properly. In this case, disable the auto termination feature, as
described in “When and How to Turn Off Auto Termination” on
page 31.
Even though the A5150A provides automatic termination, the opposite
end of the SCSI bus must still be properly terminated. If you need an
external terminator for connecting directly to the A5150A HBA, the
appropriate terminator is HP product number A5296A, “VHDCI LVD/SE
terminator.” If you need an additional terminator for connecting to a
peripheral on the end of the SCSI bus, order the appropriate terminator
needed to attach to the peripheral. See the peripheral’s documentation
for additional information.
When and How to Turn Off Auto Termination
Information about when and how you turn off auto termination for the
A5150A is given below.
When To Turn Off Auto Termination
Some sample scenarios for when you must turn off auto termination are
described below. Note that the internal connectors of the HBA are not
usually used in any of the HP 9000 servers. So, these scenarios assume
that nothing is connected to the internal connectors.