pc

10.25 pc 11.25 pc

38

 

 

34.5 pc

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 LSIU160 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 and faster 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 LSIU160

pc

may enable termination erroneously if it is directly cabled to

 

 

another SCSI device or host adapter using the same

 

sensing method. The LSIU160 senses the presence of

 

SCSI devices by detecting the ground signal on conductor

 

50 of the SCSI cable.

 

The LSIU160 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 LSIU160 host adapter for these three different bus

 

configurations is discussed below.

2-18

Installing the LSIU160