Hewlett-Packard SureStore 125ex Optical Jukebox User's Guide - C1118-90000

OPERATING THIS JUKEBOX ON A SCSI BUS

JUMP

CONTENTS

INDEX

SINGLE-ENDED, HIGH-VOLTAGE DIFFERENTIAL, AND LOW-

VOLTAGE DIFFERENTIAL INTERFACES

The SCSI bus is electrically implemented in three ways: single-ended, high-voltage differential, and low-voltage differ-

ential. 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 metres (9.8 feet).

High-voltage differential buses uses two lines for each signal and measures the voltage difference between the two sig-

nals. The differential configuration retains more signal quality than single-ended and is not as sensitive to noise, allow-

ing for a longer cable length. The maximum allowable length of a high-voltage differential bus is 25 meters (82 feet) for

all types of buses (narrow, wide, fast, Fast-20)

Low-voltage differential buses (Ultra 2) use less of a voltage difference between the two signals used for each bus sig-

nal. The low-voltage differential configuration also retains more signal quality than single-ended and is not as sensitive

to noise as either the single-ended or high-voltage differential buses. The maximum allowable length of a low-voltage

differential bus is 12 metres (39.4 feet).

CONNECTORS

50-pin connectors - narrow devices only

• 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