Weidmuller WI-MOD-945-E: 900Mhz Wireless Ethernet & Device Server v2.16 - Manual (Page 18)

Weidmuller Wireless Ethernet Modem & Device Server WI-MOD-945-E User Manual
Page 18 www.weidmuller.com Rev 2.136
RS485 Serial Port
The RS485 port provides for communication between the WI-MOD-945-E unit and its host device using a multi-drop
cable. Up to 32 devices may be connected in each multi-drop network.
As the RS485 communication medium is shared, only one of the units on the RS485 cable may send data at any one
time. Thus, communication protocols based on the RS-485 standard require some type of arbitration.
RS485 is a balanced, differential standard but it is recommended that shielded, twisted pair cable be used to interconnect
modules to reduce potential RFI. It is important to maintain the polarity of the two RS485 wires. An RS485 network should
be wired as indicated in the diagram below and terminated at each end of the network with a 120-ohm resistor. On-board
120-ohm resistors are provided and may be engaged by operating the single DIP switch in the end plate next to the
RS485 terminals. The DIP switch should be in the “1” or “on” position to connect the resistor. If the module is not at one
end of the RS485 cable, the switch should be off.
Shorter runs of 485 cables may not require the termination resistors to be enabled.
Figure 6 - Multidrop Serial
Figure 7 - End Plate