Siemens SIMATIC NET RUGGEDCOM RS920L Installation Manual page 35

Communication Ports
4.2.4 Connecting Multiple RS485 Devices
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•
•
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The following shows the recommended RS485 wiring.
2
1
1
2
3
4
5
6
Figure 4.6
26
The number of devices wired should not exceed 32, and total distance should be
less than 1219 m (4000 ft) at 100 kbps.
The Common terminals should be connected to the common wire inside the
shield.
The shield should be connected to earth ground at a single point to avoid loop
currents.
The twisted pair should be terminated at each end of the chain.
3
4
RUGGEDCOM RS920L Device
Common (Isolated Ground)
Negative
Positive
Shield to Earth (Connected At a Single Point)
RS485 Devices (32 Total)
Recommended RS485 Wiring
5
5
120Ω 10nF
120Ω 10nF
6
RUGGEDCOM RS920L
Installation Manual, 02/2020, C79000-G8976-1032-06