Connecting Multiple Rs485 Devices - Siemens Ruggedcom RS416P Installation Manual

Chapter 4
Communication Ports
Section 4.6

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.
2
1
Figure 29: Recommended RS485 Wiring
1. RUGGEDCOM RS416P 2. Common (Isolated Ground) 3. Negative 4. Positive 5. Shield to Earth (Connected At a Single Point)
6. RS485 Devices (32 Total)
30
3 5
4
120Ω 10nF
5
120Ω 10nF
RUGGEDCOM RS416P
Installation Guide
6
Connecting Multiple RS485 Devices