XBee
‐
PRO®
900HP
RS
‐
232/RS
‐
485/USB
RF
Modem
‐
Product
Manual
©
2013
Digi
International
Inc.
16
Figure
2
‐
09. RF
Modem
in
an
RS
‐
422
environment
2 .3 .3 . RS- 4 8 5 / 4 2 2 Con n e ct ion Gu ide lin e s
The RS-485/422 protocol provides a solution for wired communications that can tolerate high
noise and push signals over long cable lengths. RS-485/422 signals can communicate as far as
4000 feet (1200 m). RS-232 signals are suitable for cable distances up to 100 feet (30.5 m).
RS-485 offers multi-drop capability in which up to 32 nodes can be connected. The RS-422
protocol is used for point-to-point communications.
Suggestions for integrating the 900HP RF Modem with the RS-485/422 protocol: Twisted pair
cabling is used for the positive and negative data lines. An Ethernet cable is good for twisted pairs.
When using Ethernet twisted pair cabling:
Select wires so that TX+ and TX-are connected to a twisted pair. Likewise, select wires so that RX+
and RX- are connected to a twisted pair. (For example, tie the green and white/green wires to TX+
and TX-). This reduces the amount of noise on the data line.