SCSI Symbols

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SCSI Types / Symbols
SE SE SCSI (also called Single-Ended SCSI) – Most SCSI devices use SE SCSI signaling. In SE SCSI each signal is carried by a single wire. SE SCSI is very susceptible to noise and has a rather short distance limitation, a maximum of 6 meters. Unless a device says otherwise, it is probably a SE SCSI device.
Differential or HVD Differential SCSI (also called HVD or High Voltage Differential SCSI) – Differential SCSI is completely incompatible with SE SCSI above because it uses “differential” signaling rather than “single-ended” signaling. The benefit of using differential SCSI is that it works well in noisy areas and can reach up to 25 meters in distance. Caution: Unless a SCSI device, controller, or cable adapter specifically says “differential” or “HVD”, it will probably not work with other differential SCSI devices. Because of the benefits of LVD SCSI (below), differential SCSI is becoming less popular, however our ACC7229 can be used to connect a HVD device to a LVD bus or the other way around. Note: Never mix Differential SCSI with SE or LVD SCSI without the ACC7229 converter.</td
LVD LVD SCSI (also called “Low Voltage Differential” SCSI) – LVD is the newest type of SCSI cabling, and LVD SCSI specifications offer distances up to 12 meters and legacy support if LVD/SE which offer LVD mode or SE mode. Most LVD SCSI devices are LVD/SE, however you can only run in SE mode or LVD mode. If one device on your SCSI bus is SE, all devices will be limited to SE limitations. All devices must be set to LVD to achieve LVD distance and speed capabilities. Note that LVD SCSI cabling requires “Twist and Flat” ribbon cable and an LVD/SE terminator or a “Twist and Flat” ribbon cable with built-in LVD termination. If operating in SE mode, you only need an active terminator.
LVD/SE LVD/SE equipment is equipment that can work either LVD or SE; however, the two can’t be mixed on the same bus. The entire bus must be one or the other.