Siemens RUGGEDCOM RS416P, Руководство по установке, Страница: 40 / 54

Chapter 4
Communication Ports
RUGGEDCOM RS416P
Installation Guide
30 Connecting Multiple RS485 Devices
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.
<
12
19
m
(
40
00
in
)
120Ω 10nF
120Ω 10nF
1
2
3 5
5
6
4
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)