Mitsubishi FX Series PLC Data Communication Practical Manual

18H: Remote control error (RUN/STOP mode mismatch)

5. General troubleshooting steps

Confirm PLC version: Read the last three digits of D8001 and refer to the applicable version table in the manual.

Check hardware installation: Ensure that the expansion module is securely connected and the terminal resistance is set correctly (110 Ω or 330 Ω).

Validation parameters: Confirm that the communication format matches the device by monitoring D8120/D8400/D8420.

Check program conflicts: Avoid using RS, RS2, EXTR, or inverter instructions simultaneously on the same channel.

Clear error flag: Some errors require restarting the PLC or switching RUN/STOP to clear.

Practical suggestions

For new systems, the FX3 series PLC is preferred as it supports richer communication instructions (such as RS2, IVMC) and higher baud rates (38400bps).

N: The N network is suitable for small distributed control, but it should be noted that the link period increases with the number of stations (in Mode 2, the link time for 8 stations is about 131ms).

If computer links require frequent reading and writing of large amounts of data, it is recommended to use QW/QR commands (FX3 series) to improve efficiency.

In frequency converter communication, reasonable response waiting time (D8150/D8155) and communication retry times should be set to avoid timeouts caused by processing delays in the frequency converter.

When performing remote maintenance, it is necessary to correctly configure the modem initialization parameters (AT command) on the PLC side and register the corresponding AT command on the personal computer side.