Adaptec AHA-3940U Getting Started Guide - Page 6

When any UltraSCSI devices are connected to the host adapter and configured to run at UltraSCSI speed, the total length of all cables on the same channel (internal and external) must not exceed 3 meters (9.8 feet) to ensure reliable operation. When no UltraSCSI devices are connected, the total length of all cables must not exceed 6 meters (19.7 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 For Channel A on the AHA-3940U/3940UW, and both channels on the AHA-3940UWD, if the host adapter detects that a device is connected to its internal and external connectors, it disables its terminators. Otherwise, the terminators are enabled. s For Channel B on the AHA-3940U/3940UW, Automatic mode is the same as Enable mode. 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 J6 if the second computer is connected to SCSI Channel A or on jumper J3 if the second computer is connected to SCSI Channel B. 6 AAAAAAAAAAAAAAAAAAPPCAAAAAAaruHiAAArrntAAAArtAAAeN-SAAAn3uAAApt9mAAAeD4AAAcbAAA0aeAAANtUerAAAu::/AAA3mAAA519AAA11b4AAA1/eAAA010rAAAU4:4AAA/04WAAA9-AAA960AAA/43AAA059AAA,6AAA4R8AAA0e-AAAU0vAAA0AAA.WAAABAAADEAAAAAACIAAAnNAAAsAAAtDAAAaAAAlalAAAtaAAAetAAA:i1oAAAAAA1nAAA/G1AAAAAA8uAAA/i9AAAdAAA6eAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA