HP 800 HP DTC Cabling and Racking Guide - Page 76

Guidelines for application, Single-ended versus Differential Transmission, RS-232

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8 A note on standards Guidelines for application The RS-422 and RS-423 standards do not specify maximum distances or maximum data rates for connecting cables. These standards do, however, include "Guidelines for application" which give conservative values for maximum cable length and data rates based upon the following cable type: • twisted pair, copper • 52.5pF/meter shunt capacitance • 24 AWG The following information is based upon these guidelines. The performance achievable in a real configuration will differ from that suggested by the guidelines, as performance is also determined by the environment and the configuration itself. Single-ended versus Differential Transmission Two methods are used for sending digital signals between components (such as a system and a terminal). The first method, single-ended data transmission, is based upon the use of one signal line. The second method, differential data transmission, uses two signal lines. Single-ended data transmission is used by equipment which conforms to the RS-232 or RS-423 standards. Differential data transmission is used by the RS-422 standard. RS-232 The RS-232 standard, though widely used, has a maximum data rate of 20kBaud and cannot be used over long distances (maximum of 50 feet/15 meters). However, it has the advantage of being commonly used and understood. It can also operate with just three conductors, if necessary, for direct terminal connection. RS-232C Application Data In RS-232C Interface Data Out 70

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70
A note on standards
8
Guidelines for application
The RS-422 and RS-423 standards do not specify maximum distances or maximum
data rates for connecting cables. These standards do, however, include “Guidelines
for application” which give conservative values for maximum cable length and data
rates based upon the following cable type:
•
twisted pair, copper
•
52.5pF/meter shunt capacitance
•
24 AWG
The following information is based upon these guidelines. The performance
achievable in a real configuration will differ from that suggested by the guidelines,
as performance is also determined by the environment and the configuration itself.
Single-ended versus Differential Transmission
Two methods are used for sending digital signals between components (such as a
system and a terminal). The first method, single-ended data transmission, is based
upon the use of one signal line. The second method, differential data transmission,
uses two signal lines.
Single-ended data transmission is used by equipment which conforms to the RS-232
or RS-423 standards. Differential data transmission is used by the RS-422 standard.
RS-232
The RS-232 standard, though widely used, has a maximum data rate of 20kBaud
and cannot be used over long distances (maximum of 50 feet/15 meters). However,
it has the advantage of being commonly used and understood. It can also operate
with just three conductors, if necessary, for direct terminal connection.
Data
In
Data
Out
RS-232C
Interface
RS-232C Application