information for the standard SCSI LVD. Low Voltage Differential SCSI information from SCSI book

What is LVD (Low Voltage Differential) SCSI? And how does it affect SCSI usage? LVD- Low Voltage Differential
SCSI Information

Excerpt taken from: Making SCSI Work A Practical Guide by
The Paralan Staff
Low Voltage Differential (LVD) SCSI is an emerging standard defined in the SPI-2 document of SCSI-3 that runs on 3.3 VDC rather than 5 VDC. The goal of LVD is to allow higher data rates while combining the benefits of single-ended and differential SCSI. As with single-ended, the drivers can be integrated into the protocol chip. Like differential, LVD will be less sensitive to electromagnetic noise and allow high data rates at greater lengths than single-ended. LVD is the interface specified for use with Ultra-2 SCSI at 40 megatransfers per second, and will be used in the U160/m SCSI 80 megatransfer per second specification. Statements made under "speed and cabling considerations" of differential SCSI also apply to LVD.

Although LVD is not directly compatible with single-ended, the devices will use multimode drivers that automatically detect the type of bus used and switch into the appropriate mode of operation. This will allow you to use an LVD/SE device on a single-ended bus without having to set any switches or jumpers. Therefore, LVD has been introduced gradually without the loss of the current investment in single-ended devices.
But, it should be noted that the advantages of LVD are lost when a LVD/SE device is used in a single-ended bus. Actually, as soon as one single-ended device is connected to LVD/SE bus, the whole bus switches to single-ended mode with all its limitations.

A LVD bus can be 12 meters (40 feet) long. This is true for all speeds including Ultra-2 SCSI at 40 megatransfers/sec and a load of up to 16 devices.

As with all parallel SCSI alternatives, the LVD SCSI bus must be terminated on both ends. The LVD terminator uses a 1.25 volt source and a few resistors (see fig, 2-8). Currently there are no other termination alternatives for LVD. LVD/SE terminator chips with an auto sense feature that automatically switches termination from single-ended to LVD depending on the DIFFSENS signal are available.

For more information on this book please see: Making SCSI Work, A Practical Guide written by Paralan Staff.

For information on problem solving with our LVD products, see:

MH16/MH17
Series 80 LVD/MSE to HVD Converters.
MH19
LVD to HVD Converter for HP LTO-Ultrium Tape Drives.
MS16/MS17
Series 80 LVD/MSE to SE Converters.

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