HP Surestore 125ex Hewlett-Packard SureStore 125ex Optical Jukebox User&#1 - Page 101

Ingle, Ended, Oltage, Ifferential, Nterfaces, Onnectors

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B NEXT PREVIOUS JUMP CONTENTS INDEX OPERATING THIS JUKEBOX ON A SCSI BUS SINGLE-ENDED, HIGH-VOLTAGE DIFFERENTIAL, AND LOWVOLTAGE DIFFERENTIAL INTERFACES The SCSI bus is electrically implemented in three ways: single-ended, high-voltage differential, and low-voltage 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 metres (9.8 feet). High-voltage differential buses uses two lines for each signal and measures the voltage difference between the two signals. The differential configuration 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 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 signal. 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 6

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B
O
PERATING
T
HIS
J
UKEBOX
ON
A
SCSI B
US
B
6
NEXT
PREVIOUS
JUMP
CONTENTS
INDEX
S
INGLE
-
ENDED
, H
IGH
-V
OLTAGE
D
IFFERENTIAL
,
AND
L
OW
-
V
OLTAGE
D
IFFERENTIAL
I
NTERFACES
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).
C
ONNECTORS
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