© Microhard Systems Inc.
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Appendix A: RS485 Wiring
The IPn3G 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 IPn3G seize control of the line at the
proper time when it is to transmit data.
Figure A1: 2-Wire RS485 Wiring
Figure A2: 4-Wire RS485 Wiring
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.
