LSI SYM8953U - Manual (Page 34)

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2-18 Installing the SYM8953U Host Adapter
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 SYM8953U host adapter 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, you must only have
LVD devices on the bus. Do not mix any SE devices with
LVD devices or the entire bus will drop to SE, limiting bus
performance to Ultra SCSI levels.
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 type/setting for each
device and how to set/change it.
Caution: The autoenable/disable sensing feature on the SYM8953U
may enable termination erroneously if it is directly cabled to
another SCSI device or host adapter using the same
sensing method. The SYM8953U senses the presence of
SCSI devices by detecting the ground signal on conductor
50 of the SCSI cable.
The SYM8953U automatically controls SCSI bus termination for three
different bus configurations, depending on how it is connected (see
Figure 2.1 ). The three bus configurations are:
•
Section 2.2.6.1, “Internal Bus Connections”
•
Section 2.2.6.2, “External Bus Connections”
•
Section 2.2.6.3, “Internal and External Bus Connections”
Termination on the SYM8953U host adapter for these three different bus
configurations is discussed below.