Adaptec USB2Xchange User Guide - Page 35

Understanding SCSI You generally set the SCSI ID on external SCSI devices by setting a switch on the back of the device. However, for specific instructions on setting the SCSI ID of your devices, refer to the devices' documentation. Terminating the SCSI Bus Your SCSI bus is a chain of devices with electrical signals running back and forth between them. If the SCSI bus is not properly terminated, any signal travelling down the bus bounces back when it hits the end of the bus, and interferes with itself. By terminating both ends of the SCSI bus, you ensure reliable communication on the bus by preventing this interference. Termination is permanently enabled on the USB2Xchange adapter, since it is always at one end of the SCSI bus. You must enable termination on the device at the other end of the SCSI bus and disable termination on each device connected between the physical ends of the bus. Most SCSI devices come from the factory with termination enabled. You usually control termination on external SCSI devices by installing or removing a SCSI terminator module (similar to the one shown in the figure below), or by setting a switch on the back of the device. However, methods for setting termination vary and you should refer to each SCSI device's documentation for detailed instructions. Terminator Note: Some SCSI devices require that termination power be supplied to the SCSI bus. The USB2Xchange adapter does not supply termination power. To use these devices with the USB2Xchange, a device which does supply termination power must be added to the SCSI bus. 25