LSI LSIU40SE Value Line, User Manual

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Detailed Installation Procedure 2-19
2.2.6 SCSI Bus Termination
The devices making up the SCSI bus are connected serially (chained
together) with SCSI cables. The first and last physical SCSI devices
connected on the ends of the SCSI bus must have their terminators
active. All other SCSI devices on the bus must have their terminators
removed or disabled. Remember that the LSIU40SE is also on the SCSI
bus—its termination is automatically enabled when it is connected to the
end of the bus.
The peripheral device terminators are usually set with jumpers, resistor
modules, or with a switch on the peripheral. Refer to the peripheral
manufacturer’s instructions and to the user’s manual for your computer
for information on how to identify the terminator setting of each device
and how to change it.
Caution: The autoenable/disable sensing feature on the LSIU40SE
may enable termination erroneously if it is directly cabled to
another SCSI device or host adapter using the same
sensing method. This is dealt with by properly setting the
termination override switches U1 or U2 (see
Figure 2.1 ).
The LSIU40SE senses SCSI devices by detecting the
ground signal on pin-22 of a 50-conductor internal SCSI
ribbon cable, or pin-50 of an internal or external
68-conductor SCSI cable. If you use an adapter to connect
8-bit devices externally with a 50-conductor SCSI cable, the
ground signal is detected on pin-34.
The LSIU40SE automatically covers SCSI bus termination for five
different bus configurations, depending on the use of the connectors on
the LSIU40SE (see
Figure 2.1 ). The five bus configurations are:
•
Only for internal SCSI connections,
•
Only for external SCSI connections,
•
For both internal and external SCSI connections,
•
For connections to both internal connectors, and
•
For an internal connection to another LSIU40SE, or any connection
to a device using the same sensing method for automatic termination
as your LSIU40SE.