Connecting Multiple Rs485 Devices - Siemens RUGGEDCOM RS400 Installation Manual

RUGGEDCOM RS400
Installation Guide
Port
1
2
3
4
The following is the pin-out description for the RS485 insulated terminals:
Figure 20: Serial Insulated Terminal Port
Section 4.4.5

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.
Connecting Multiple RS485 Devices
Jumper Number
JP5
JP6
JP7
JP8
1 2 3
Jumper Position
No Termination
Removed
Terminal
1
2
3 Common (Isolated Ground)
Chapter 4
Communication Ports
AC Termination
Installed
Description
Positive
Negative
23