Connecting Multiple Rs485 Devices - Siemens RUGGEDCOM RS416P Installation Manual

RUGGEDCOM RS416P
Installation Guide
• Off – No signal detected
Section 3.5

Connecting Multiple RS485 Devices

Each RS485 port can communicate with multiple RS485 devices by wiring devices together in sequence over a
single twisted pair with transmit and receive signals on the same two wires (half duplex). For reliable, continuous
communication, adhere to the following guidelines:
• To minimize the effects of ambient electrical noise, use shielded cabling.
• The correct polarity must be observed throughout a single sequence or ring.
• 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.
The following shows the recommended RS485 wiring.
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1
Figure 30: Recommended RS485 Wiring
1. RUGGEDCOM RS416P
6. RS485 Devices (32 Total)
Connecting Multiple RS485 Devices
3 5
4
120Ω 10nF
2. Common (Isolated Ground)
5
120Ω 10nF
3. Negative 4. Positive 5. Shield to Earth (Connected At a Single Point)
Chapter 3
Communication Ports
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