Chapter 4
Communication Ports
RUGGEDCOM RS910W
Installation Guide
28
Connecting Multiple RS485 Devices
1
2
Figure 20: RS232/RS485/RS422 Fiber Serial Console Ports
Pin
Name
1
Rx
2
Tx
Section 4.4.4
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.
