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Appendix C: RS-485 Wiring
Appendix C: RS-485 Wiring
The MDR100A-R5 or MDR112A-R5 can be connected into a 2-wire or 4-wire RS-485 network. Terminate the transmission line
only at the extreme ends of the data line if the RS-485 network runs at high data rates and has a long wiring run.
2-wire RS-485
Figure C-1 shows a typical two-wire configuration for an RS-485 connection to a MDR100A-R5 or MDR112A-R5. Two wires are
shared for transmitting and receiving in a 2-wire configuration, so the modem must seize the line at the right time when it trans-
mits. Note again that a transmission line termination is required if the system has high data rates and long wiring runs.
Figure C-1. 2-wire RS-485 Configuration.
4-wire RS-485
A MDR100A-R5 or MDR112A-R5 can also be connected into a RS-485 network in a four-wire configuration as shown in Figure
C-2. In a four-wire network, one node must be a master node and all others must be slaves. The network is connected so that the
master node communicates to all slave nodes. All slave nodes communicate only with the master node. Since the slave nodes
never listen to another slave response to the master, a slave node cannot reply incorrectly to another slave node.
Figure C-2. 2-wire RS-45 Configuration.
