Reference Manual

Table Of Contents
9. Additional Radio Information
LUM0020CD Rev June-2020 Page 91 of 112 Copyright © 2019FreeWave
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When setting the radio to RS485:
1. Enable Modbus.
2. Set Master Packet Repeat to 3 in the radios that use RS485.
3. Set Turn Off Delay to 4.
The Turn Off Delay setting in the menu is used to control the length of time the transmitter driver
stays asserted after data transmission has finished.
l This is needed to allow the last transmitted character to reach the end of a long line and is
normally set to one character length of time.
l This setting also allows three complete reflections to the end of the line to ensure the ringing
on the line has fully dampened before releasing the bus to another device.
FREEWAVE Recommends: Shorter line lengths may use shorter delays, but four one-quarter-
character delay times are recommended.
Note: In Modbus, a Turn Off Delay setting of 0 causes internal timing errors.
Important!: There is no provision for hand shaking in any of the modes of operation.
Data rates above 9600 bps in RF Data Rate = 5 and above 19200 bps in RF Date Rate = 4 are NOT
recommended without a protocol that can handle error detection properly.
9.1.1. RS422 and RS485 Full Duplex Pinouts
Function Bare Board Pin Number DB-9 Pin Number
RX+ 7 3
RX- 9 7
TX+ 5 2
TX- 10 8
Signal Ground 4 or 6 5
9.1.2. RS485 Half Duplex Pinout
Function Bare Board Pin Number DB-9 Pin Number
Wire to both bins for Bus + Short 5 and 7 Short 2 and 3
Wire to both pins for Bus - Short 9 and 10 Short 7 and 8
Signal Ground 4 or 6 5
LRS455A-C, LRS455A-CE, LRS455-T
User-Reference Manual
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