Cautions On Communication Setup - Mitsubishi FX3U Series User Manual

FX Series Programmable Controllers
3U
User's Manual - MODBUS Serial Communication Edition
5.4

Cautions on Communication Setup

1. Timing of Communication Parameters
Though the MODBUS communication parameters are setup using the PLC program, the parameters become
effective only after the PLC power is switched from OFF to ON.
2. N:N Networking and MODBUS Communication
If N:N Networking and MODBUS communication are setup for the same channel, the N:N Networking will
operate however the MODBUS settings will be ignored.
If this situation occurs, a "channel double use" error (Error Code #203 in D8402 or D8422) will be displayed
for the corresponding channel within the PLC.
3. Using the MODBUS Configuration Request Flag (M8411)
The Auxiliary Relay M8411 is a special relay used for MODBUS Serial Communication setup only. Do not use
the PLC ladder program or any other External Devices to set or reset this relay at any time. Do not use any
coils or conditionals before the MODBUS Configuration Request Flag or between the MODBUS Configuration
Request Flag (M8411) and the MOV commands.
Using other coils or conditionals before or after the MODBUS Configuration Request Flag during
Communication Setup will invalidate the MODBUS Communication Parameters and thereby disable
MODBUS Serial Communication.
4. Communication Setup Syntax
All MODBUS Communication Parameters must be setup using the MOV command and Constants, meaning
a K or H value.
Using non-constant/indirect devices during communication setup will invalidate the MODBUS Communication
Parameters and thereby disable MODBUS Serial Communication.
→ For details on MODBUS errors and error devices, refer to Chapter 12.
5 Communication Setup
5.4 Cautions on Communication Setup
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