RuggedCom RS416 - Manual (Page 29)

Serial Ports
29
RuggedCom ® RuggedServer™ RS416 Family Installation Guide rev118
3.6 RS485 Wiring
Each RS485 port can communicate to multiple RS485 devices by daisy chaining devices
over a single twisted pair with transmit and receive signals on the same two wires (half
duplex). The following guidelines should be followed to ensure reliable continuous
communication:
1. To minimize the effects of ambient electrical noise, shielded cabling is
recommended.
2. The correct polarity must be observed throughout a single daisy chain.
3. The number of devices wired should not exceed 32, and total distance should be
less than 4000 feet (at 100 kbps).
4. The Common terminals should be connected to the common wire inside the
shield.
5. The shield should be connected to earth ground at a single point to avoid loop
currents
6. The twisted pair should be terminated at each end of the chain.
The figure below shows the recommended RS485 wiring.
Figure 23: Conceptual recommended RS485 wiring diagram