Appendix C: Rs485 Wiring - Cal Amp Phantom II Operating Manual

Appendix C: RS485 Wiring

© CalAmp
The Phantom II can be connected into a 2– or 4-wire RS485
network. A transmission line termination should be placed only on
the extreme ends of the data line if the RS485 network runs at high
speed and the cable run is very long.
2-Wire
Figure C1 illustrates a typical 2-wire RS485 wiring configuration.
The cable pair is shared for both transmit and receive data: it is
very important that the Phantom II seize control of the line at the
proper time when it is to transmit data.
4-Wire
In a 4-wire network, one node will be the master and all other nodes
will be remotes. The master node may talk to all remote nodes, yet
each remote may only communicate with the one master. Since the
remote nodes never 'hear' each other, a remote node could not
conceivably reply incorrectly to another remote's communication.
Phantom II
Figure C-1: 2-Wire RS485 Wiring
Figure C-2: 4-Wire RS485 Wiring
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