Siemens RUGGEDCOM RMC20 Installation Manual page 24

Chapter 3
Communication Ports
NOTE
The RUGGEDCOM RMC20 features built-in pull-up and pull-down resistors. As such, external bias
resistors are only recommended when connecting the RUGGEDCOM RMC20 to third-party serial devices
that do not have built-in pull-up and pull-down resistors.
NOTE
Transient protection is provided on all terminals. Lightning strikes and ground surge currents can cause
large momentary voltage differences between ends of communication links. For maximum reliability of
the entire link, all equipment should have similar transient protection installed.
The following shows the recommended RS485 wiring.
2
1
Figure 14: Recommended RS485 Wiring
1. RUGGEDCOM RMC20 Device With Built-In Termination 2. Common (Isolated Ground) 3. Negative 4. Positive 5. Shield to Earth
(Connected At a Single Point) 6. RS485 Devices (32 Total)
18
3 5
4
5
120Ω 10nF
RUGGEDCOM RMC20
Installation Guide
6
RS485/422 Data Ports