Specifications

Chapter 2 - System Configuration RS-422 And RS-485 Applications Ebook
Page 25 of 137 Manual Documentation Number: <DocNumber>
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Network Topologies
The topology of a network describes the physical or logical
configuration of the nodes on the network. The EIA standards do not
define network topologies for RS-422 and RS-485. A variety of
topologies can be used, although in practice some topologies work
better than others, for reasons explained in the following sections.
RS-485 two and four-wire networks can be connected in a variety of
topologies (bus, ring, star, tree, etc), especially when baud rates are
relatively low, distances are short and noise is limited. However, for
simplicity and reliable results many experienced users suggest using a
daisy chain network configuration. However, the physical requirements
of the application may dictate other connections and layouts.
RS-422 is most commonly used in point-to-point links. But when RS-
422 is used in point-to-multipoint connections, or when RS-422 is used
as the master in a four-wire master-slave network, the same network
topology considerations apply.
Figure 16: Daisy Chain Network Topology
Note: The Methods of Termination (on page 29) section discusses how network topology relates
to the placement of termination resistors.
Two-Wire Systems
The tristate capabilities of RS-485 allow a single pair of wires to share
transmit and receive signals for half-duplex communications. Although
this is commonly referred to as a "two-wire" configuration, an