Hp Optical Jukeboxes Bedienungsanleitung PDF herunterladen (Seite 86)

B-5 Appendix B

Operating This Jukebox on a SCSI Bus

A Brief Overview of SCSI

Termination is always at both physical ends of the bus.

Single-ended and Differential Interfaces

The SCSI bus is electrically implemented in two ways: single-ended and

differential. These terms come from the way the signals are asserted on the bus.

Single-ended buses use a 5-volt signal that is referenced to ground. This method

makes the bus somewhat susceptible to noise and loss of signal quality over

distance. The maximum allowable length of a single-ended SCSI bus was initially 6

meters (19.7 feet). Fast SCSI required the maximum length of the bus to be reduced

to 3 meters (9.8 feet).

The differential bus uses two lines for each signal and measures the voltage

difference between the two signals. Differential retains more signal quality than

single-ended and is not as sensitive to noise, allowing for a longer cable length. The

maximum allowable length of a differential bus is 25 meters (82 feet) for all types

buses (narrow, wide, fast, Fast-20).

Connectors

Narrow devices (50-pin) use the following connectors:

• 50-pin low-density clip Centronics-type (external)

This is a large connector that is similar to a printer cable. This type of connector

is gradually being replaced by the Micro D connector, described below.

• 50-pin high density Micro D (using thumbscrews or small clips) (external)

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Hp Optical Jukeboxes Bedienungsanleitung Seite 86