Reference Manual

Table Of Contents
9. Additional Radio Information
This section contains additional important information about the FreeWave radios described in
this manual.
l Operational RS422 and RS485 Information
l RS422 and RS485 full duplex pin-outs
l RS485 half duplex pin-outs
9.1. Operational RS422 and RS485 Information
For RS422 and RS485, the FreeWave radio can drive 32 standard unit loads and loads the bus
with only 1/8 unit load. This allows a maximum of 256 devices on the bus if all of the line receivers
have 1/8 unit load.
RS422 is used for 4-wire or full duplex communication with one Master and multiple Slave radios.
l The Master radio keeps the line driver asserted at all times.
l The maximum line length is 4,000 feet using two, 120 ohm twisted pair cables with a fifth
wire for data common.
l RS485 full duplex using 4-wire plus common is the same as RS422, except the system can
have multiple Masters on the bus.
The most common operation of RS485 is a two-wire comprised of a 120 ohm impedance single
twisted pair.
In this system the loading of the FreeWave radio is as described above, which allows up to 256 1/8
unit load units on the bus.
Maximum line length is also 4,000 feet with a third wire required for data common.
The FreeWave radio checks the line to be certain no other device is transmitting before enabling
the line driver for data transmission.
LUM0020CD Rev June-2020 Page 90 of 112 Copyright © 2019FreeWave
This document is subject to change without notice. This document is the property of FreeWave Technologies, Inc.
and contains proprietary information owned by FreeWave. This document cannot be reproduced in whole or in
part by any means without written permission from FreeWave Technologies, Inc.
LRS455A-C, LRS455A-CE, LRS455-T
User-Reference Manual