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PRODUCT INSTALLATION MANUAL
2.7.3.
RS-485
An RS-485 network permits up to 32 devices to communicate over a maximum of 1200m (4000 ft) of cable.
The length of this network can be extended if necessary by using RS-485 repeaters. The communication
occurs via a differential signal over a shielded twisted pair of wires. Per the RS-485 specification the signal
wires should be labeled "A" and "B", but sometimes a "+" and "-" are used instead. In these cases connect
the "+" to "B" and the "-" to "A".
NOTE: A MUX 2700 that is cross-wired on the RS-485 network will not be damaged, but it
also will not communicate.
Since the MUX 2700 is optically isolated it is important to link the signal grounds of the different network
nodes to the host ground through the cable shield. This helps prevent ground potential differences from
causing a loss of data or damage to equipment on the RS-485 network.
Many cable manufacturers make cable specifically designed for RS-485 networks. Pepperl+Fuchs Elcon
recommends using shielded twisted pair cabling and then utilizing the shield as the RS-485 network ground.
This shield should be grounded at the RS-485 converter if possible.
RS-485 wiring must be connected as shown in Figure 2. These wires carry data from the HIS to the PC via
an RS-485/RS-232 converter cable. Connect the converter to a serial port on the PC as indicated in the
converter's documentation.
Figure 2 – RS-485 Wiring
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