Serial Insulated Terminals; Connecting Multiple Rs485 Devices - Siemens RUGGEDCOM RS400 Installation Manual

Chapter 3
Communication Ports
Section 3.4.3

Serial Insulated Terminals

The RS400 can be equipped with serial RS485 insulated terminals. The terminals are terminated by default from
the factory. Termination provided is AC Termination style 120 Ohm resistor in series with a 10nF capacitor. The
following details the appropriate jumper configuration for each RS485 port.
Port
1
2
3
4
The following is the pin-out description for the RS485 insulated terminals:
Figure 19: Serial Insulated Terminal Port
Section 3.4.4

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.
18
Jumper Number
JP5
JP6
JP7
JP8
1 2 3
Jumper Position
No Termination
Removed
Terminal
1
2
3 Common (Isolated Ground)
RUGGEDCOM RS400
Installation Guide
AC Termination
Installed
Description
Positive
Negative
Serial Insulated Terminals