12. Troubleshooting; 12.1 Checking The Fx3U Plc Version Applicability; Checking The Communication Status Based On Led Indication; Checking The Installation And Wiring - Mitsubishi FX3U Series User Manual

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

12. Troubleshooting

This chapter explains troubleshooting.
12.1 Checking the FX
Verify that the FX
12.2

Checking the Communication Status Based on LED Indication

Check the status of the "RD" and "SD" indicator LEDs provided in the optional equipment.
RD
Flashing
Flashing
Off
Off
While MODBUS serial communication is functioning normally, both LEDs flash brightly.
If they are not flashing, check the wiring, communication settings, and error statuses of the master and slave
stations.
12.3

Checking the Installation and Wiring

1. Mounting status
Verify that the communication equipment is securely connected with the PLC. If the communication
equipment is not securely connected, communication will not function correctly.
→ For the mounting method, refer to the respective communication equipment manual.
2. Wiring
Verify that all communication equipment is correctly wired. If the wiring is incorrect, communication will not
function correctly.
12.4

Checking the Communication Settings and Sequence Program

1. Communication setting using sequence program
Verify that the communication format registers (D8120, D8400 and D8420) are being set correctly. If a
communication port is set twice or more, communication is disabled.
After changing any settings, make sure to reboot the PLC's power.
PLC Version Applicability
3U
Series PLC main unit is an applicable version.
3U
LED status
SD
Flashing
Off
Flashing
Off
→ For the MODBUS communication settings, refer to Chapter 5.

12.1 Checking the FX3U PLC Version Applicability

→ For the version applicability check, refer to Section 1.3.
Opeartion status
Data is being sent and received.
Data is received, but is not sent.
Data is sent, but is not received.
Data is not sent nor received.
→ For the wiring check method, refer to Chapter 4.
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