Home Site Map Contact Us
Paralan CorporationMaking SCSI WorkPurchase SCSI products online at new Paralan Store
About Paralan        SCSI Products        Literature        About SCSI        Support        News        How to Buy
paralan home

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.

Making SCSI Work, A Practical Guide, by Paralan Staff


  • 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.

LVD Configuration

  • 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.

LVD Termination

  • 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.
Paralan Corportion address
About Paralan | Products | Literature | About SCSI | Support | News | How to Buy

Paralan Corporation 4655 Ruffner Street, San Diego, CA 92111
Sales: (800) 479-7719 | Tel.: (858) 560-7266 | Fax: (858) 560-8929 | E-mail: info@paralan.com
Copyright 2006-2008 Paralan Corporation
Custom Search