Adaptec 3940AUW Installationsanleitung PDF herunterladen (Seite 7)

AHA-3940AU/AUW Installation Guide

Part Number: 511418-00, Rev. A

Print Spec Number: 496346-00

Current Date: 3/12/97 ECN Date:3/10/97

If you want to connect only SCSI-1 or SCSI-2

devices (no UltraSCSI devices), the maximum

total cable length 6 meters (19.7 feet). If you want

to connect 4 or fewer UltraSCSI devices, the maxi-

mum total cable length is 3 meters (9.8 feet). For

configurations with 5 or more UltraSCSI devices,

maximum total cable length is 1.5 meters(4.9 feet).

See your device’s documentation to determine

whether it is an UltraSCSI device.

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

SCSISelect utility. The default setting is Automatic,

which works like this:

■

If the host adapter detects that devices are con-

nected to both connectors on Channel B, it dis-

ables its terminators. Otherwise, the terminators

are enabled.

■

For the AHA-3940AU, since there is only one con-

nector for Channel A, termination for this channle

is always enabled.

For the AHA-3940AUW, if the host adapter

detects that devices are connected to two of the

three connectors on Channel A, it disables its ter-

minators. Otherwise, the terminators are enabled.

If you need to change host adapter termination, com-

plete the physical installation, then run SCSISelect as

described in Configuring the Host Adapter on page 8.

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 J3 on the 3940AU or J6 on the 3940AUW if

the second computer is connected to SCSI Channel A

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