Adaptec 3940AUW Installation Guide - Page 7

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 maximum 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: s If the host adapter detects that devices are connected to both connectors on Channel B, it disables its terminators. Otherwise, the terminators are enabled. s For the AHA-3940AU, since there is only one connector 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 terminators. Otherwise, the terminators are enabled. If you need to change host adapter termination, complete 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 provide 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 6 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