KTI Networks KSC-240, Installation Manual

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3.4 RS-485 Half-duplex 2-wire Network
This is the typical RS-485 topology. It takes advantage of RS-485 capabil-
ity to support multiple drivers on a bus. RS-422 devices should not be
used in this configuration. This topology enables bidirectional communi-
cation from many nodes over long distances at low to medium data rates,
all on a single pair of wires (2-wire).
It can implement a very functional, very flexible and very economical data
network. Because signals travel in both directions, this bus should be
terminated at both ends to prevent reflections. Only one node can drive
the bus at a time, making this a half-duplex communication channel. Only
one driver should be active at any one time. Therefore the transceivers
used on a half-duplex bus should support a
Driver Enable function.