Single-ended Buses
A single-ended SCSI bus uses signals that are either 5 Volts or 0 Volts (indeed,
TTL levels) and are relative to a COMMON ground reference. A single ended 8 bit
SCSI bus has approximately 25 ground lines, which are all tied to a single 0 volt
‘rail’ on all devices. A standard single ended bus has a maximum length of 6 meters.
If the same bus is used with fast-SCSI devices, the maximum length allowed drops
to 3 meters. Fast-SCSI means that instead of 5Mbytes/sec the bus allows 10Mbytes/sec
transfers.
Note that this means that if some devices on your bus use 'fast' to communicate
your bus must adhere to the length restrictions for fast buses!
It is obvious that with the newer fast-SCSI devices the bus length can become a
problem for large installations. This is why the differential SCSI bus was introduced
in the SCSI-2 standard.
For connector pinning and connector types please refer to the SCSI-2 standard.
Connectors etc are listed there in painstaking detail.