Adaptec AHA-3940 Installation Guide download pdf (Page 7)

Caution:

Channel A has three SCSI connec-

tors: J1, J5, and J8. Do not connect devices to

all three connectors at one time. At most,

only two of the three channel A connectors

can be used at the same time.

Terminating the SCSI Bus

The last physical SCSI device on each end of the SCSI

bus must be terminated. Termination must be

disabled on all other devices in the middle of the

SCSI bus. You may need to change the termination

setting on some devices in your computer system.

Terminating the Host Adapter

Host adapter termination is controlled by the

SCSI

Select

utility. The default setting is

Automatic

which works like this:

■

If the host adapter detects that devices are

attached to at least two connectors on channel A,

it disables its terminators. Otherwise, the termi-

nators are enabled. If the 50-pin connector is

used, the high byte termination is always

enabled.

■

Termination for Channel B is the same as channel

A, except that the internal 50-pin connector does

not apply.

If you need to change host adapter termination, com-

plete the physical installation, then run SCSI

Select

described

Configuring the Host Adapter

on page 9.

Termination in Multiple Computer Configurations

If you are setting up your SCSI bus so that SCSI

devices are shared by host adapters in two different

computers, you can enable your host adapter to pro-

vide termination power even when one computer is

powered

OFF

. To do this, place a jumper shunt on

jumper J7 if the second computer is connected to

SCSI Channel A or on jumper J6 if the second com-

puter is connected to SCSI Channel B.

This feature works only when one computer is

turned off, and the other computer connected to the

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Adaptec AHA-3940 Installation Guide Page 7

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