Communication Ports
4.4.5 Connecting Multiple RS485 Devices
The following is the pin-out description for the RS485 insulated terminals:
1
2
3
Figure 4.11
Serial Insulated Terminal Port
Terminal
Description
1
Positive
2
Negative
3
Common (Isolated Ground)
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.
RUGGEDCOM RS400
Installation Manual, 01/2021, C79000-G8976-1016-11
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