© Microhard Systems Inc. CONFIDENTIAL 167
IP9xx Series
Appendix C: RS485 Wiring
The IP9xx 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 IP9xx seize control of the line at the proper
time when it is to transmit data.
Figure C1: 2-Wire RS485 Wiring
Figure C2: 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.
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