Communication Ports
4.3.4 Connecting Multiple RS485 Devices
4.3.4
Connecting Multiple RS485 Devices
Each RS485 port can communicate with multiple RS485 devices by wiring devices to-
gether 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.
<
12
19
m
(
40
00
in
)
120Ω 10nF
120Ω 10nF
1
2
3
5
5
6
4
1
RUGGEDCOM RS910 Device
2
Common (Isolated Ground)
3
Negative
4
Positive
5
Shield to Earth (Connected At a Single Point)
6
RS485 Devices (32 Total)
Figure 4.11
Recommended RS485 Wiring
26
RUGGEDCOM RS910
Installation Manual, 02/2020, C79000-G8976-1029-09
