CONVERTING SCSI

Single-ended SCSI to Differential (HVD or LVD) SCSI Conversion

Many SCSI devices use the single-ended SCSI interface because of lower cost. Higher end computers typically use HVD differential SCSI for improved noise immunity, increased drive stability and the longer attainable cable lengths. HVD and single-ended are not directly compatible but using Paralan SE to HVD Converters allow mixing of these devices in the same SCSI domain.

Within the last few years LVD differential SCSI arrived offering greater data throughput and long cable length. Multimode LVD (LVD/MSE) offers some compatibility between single-ended and LVD. However, if a multimode LVD bus has even one single-ended device connected to it, the entire bus switches to the single-ended mode with its lower data throughput and shorter cable lengths. Using a Paralan SE to LVD Converter allows the LVD devices to operate in the LVD mode at LVD data throughput and cable length and the SE devices to operate at their throughput and cable length.

HVD SCSI to LVD SCSI Conversion

Over the last few years, higher end computers have used HVD SCSI controllers almost exclusively and frequently offer no alternative. Replacement HVD disk drives are no longer available and there is no direct compatiblity between the HVD bus and the LVD drives. However, use of a Paralan HVD to LVD Converter allows placing LVD drives on the HVD bus or, of course, HVD devices on an LVD bus.

Narrow to Wide SCSI Conversion

Frequently Wide (16-bit) SCSI devices must be connected to a Narrow (8-bit) SCSI bus or Narrow devices must be connected to a Wide SCSI bus. If this is not done with proper termination of the upper byte it can cause a multitude of very difficult to troubleshoot problems. If the Wide and Narrow devices have the same SCSI interface (both SE, both HVD or both LVD), the easiest, best and most reliable way to interconnect them is with a Paralan SCSI Isolating RegeneratoR™. If they have different SCSI interfaces, use a SE to HVD, SE to LVD or LVD to HVD Converter. In all cases, all lines will be properly terminated.

Paralan can match your SCSI needs with custom SCSI components, modifications to standard Paralan products, or even with custom systems! Paralan is ready to meet your exact requirements by applying our SCSI-savvy engineering - from SASI through Ultra320.

For a discussion of SCSI Converters and other expander techniques, see Marc Brooks' article for Computer Technology Review, The Case for SCSI Expanders or Expanding the SCSI Bus.