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2008 RuggedCom Inc. All rights reserved
Rev104
4.6.4 RS485 Wiring
Each RS485 port can communicate to multiple RS485 devices by daisy chaining devices over a
single twisted pair with transmit and receive signals on the same two wires (half duplex). The
following guidelines should be followed to ensure reliable continuous communication:
1.
To minimize the effects of ambient electrical noise, shielded cabling is recommended.
2.
The correct polarity must be observed throughout a single daisy chain.
3.
The number of devices wired should not exceed 32, and total distance should be less than
4000 feet (at 100 kbps).
4.
The Common terminals should be connected to the common wire inside the shield.
5.
The shield should be connected to earth ground at a single point to avoid loop currents
6.
The twisted pair should be terminated at each end of the chain.
The figure below shows the recommended RS485 wiring.
Figure 18: Conceptual recommended RS485 wiring diagram
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