LSI U80ALVD - Manual (Page 36)

2-18 Installing the LSIU80ALVD
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 LSIU80ALVD is also on the
SCSI bus—its termination is automatically enabled when it is connected
to the end of the bus.
Important: To utilize Ultra2 SCSI performance, the user must only have
LVD devices on the bus. Do not mix any SE devices with
LVD devices as the entire bus will drop to SE with
maximum Ultra SCSI performance.
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
LSIU80ALVD may enable termination erroneously if it is
directly cabled to another SCSI device or host adapter
using the same sensing method. The LSIU80ALVD senses
the presence of SCSI devices by detecting the ground
signal on conductor 50 of the SCSI cable.
The LSIU80ALVD automatically controls SCSI bus termination for three
different bus configurations, depending on the use of connectors (see
Figure 2.1 ). The three bus configurations are:
•
Only for internal SCSI connections,
•
Only for an external SCSI connection, and
•
Connections to both internal and external SCSI connectors.
Termination on the LSIU80ALVD for these three different bus
configurations is discussed below.