Types of SCSI Bus SignalingFitness Equipment
Types of SCSI Bus Signaling
SCSI bus signaling specifies the method that is used by the SCSI devices to communicate with each other. You should be careful not to connect the devices implementing Single-Ended (SE), low-Voltage Differential (LVD) or High-Voltage Differential (HVD) together directly, as you may damage the hardware. You can connect the single ended signaling (SE) and differential signaling devices using a SCSI expander called a Single-ended to Differential Converter and the LVD and HVD devices using the LVD to HVD connector.
Single ended signaling system transmits a positive voltage through a signal line to the receiver. The receiver returns the signal back through the ground line. The highest cable length is 6 meters. Each signal is transmitted over a single wire. Logical 1 is represented by a positive voltage and 0 as ground.
In SE, the system sends instructions that should be transmitted from the device to the SCSI controller. The controller generates the signal and sends it to all the devices over the SCSI. The devices implementing the SE signaling has a symbol on them.
Low-Voltage Differential (LVD)
In LVD, the SCSI controller sends signals to the device using the SCSI cable. The SCSI device adapter has a small transceiver built into it. The transceiver accepts the signals and resends it to the next SCSI device. This continues till the appropriate device receives the signal. The Transceiver boosts the signal. The LVD easily integrates up to 16 devices on the SCSI bus using 12 meters of cable. The devices implementing the LVD signaling have a symbol on them. LVD is cheaper compared to high Voltage Differential (HVD) but costlier than SE. Signals are transmitted using the difference in the voltage between the two wires. LVD uses 3.3 voltages to represent logical 1 or 0. The maximum cable length of LVD can be up to 12 meters using point to point connection.
High Voltage Differential (HVD)
In HVD the SCSI controller sends signals to the device using the SCSI cable. The SCSI device has a transceiver that accepts the signal and resends it to the next SCSI device. This continues till the appropriate device receives the signal. The transceiver boosts the signal and enables the maximum length for the cables to be 25 meters.
Low- Voltage Differential / Single- Ended Multi- mode (LVD/SE)
The device that uses this signaling is compatible with both the LVD and SE signaling. However if there is a device that uses the SE signaling on the SCSI Bus, then this will be set to use the SE Signaling. The devices implementing the LVD/SE signaling have a symbol on them.