Specifications

Chapter 2 - System Configuration RS-422 And RS-485 Applications Ebook
Page 30 of 137 Manual Documentation Number: <DocNumber>
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Parallel Termination
Parallel termination is the addition of a single termination resistor
somewhere along the communications line. Ideally termination
resistance should be added at the point on the communications line
furthest from the driver sending the signal. This works best on a point-
to-point link, or an RS-422 four-wire communications system in which
a driver at one end sends to a receiver at the other. The value of the
termination resistance should be close to the specified characteristic
impedance of the cable.
Figure 20: Terminating Point-to-Point Connections
More complex network topologies, such as star and tree, make it more
difficult to determine where the extremities of the network are and,
hence, the best location for termination. Also, unterminated network
stubs--especially longer ones--can add reflections that may
compromise network communications.
Bidirectional Termination
Bidirectional termination is dividing the termination resistance into two
parts and placing them (preferably) at the extreme ends of the
communications line. This is recommended when operating a two-wire
multidrop bus because data travels in both directions.