6.1. Cables

All cables used in PnP SCSI system must meet the cable specifications defined in clause 6 (SCSI bus cables) of the SCSI-3 Parallel Interface draft standard.

In mixed configuration systems, reliability is enhanced by the following provisions.

The SCSI bus segment in the host adapter should be of minimal length and capacitance. Where significant length is unavoidable, the bus layout on the board should follow transmission line principles and SPI impedance requirements.

The overall length of the internal bus segment should be minimized. The internal bus is either a SPI compliant backplane or a SPI compliant ribbon cable (examples: 3M 3801 .050 pitch 26 AWG PVC dielectric--89 ohms, or 3M 3749 .025 pitch 30 AWG TPE dielectric--85 ohms or equivalent).

Note Conventional ribbon cable (.050 pitch, 28 AWG, PVC dielectric--108 ohms) generally will work in internal configuration (only) implementations, even though it is not compliant with the SPI impedance requirements.