User`s manual

103
FX3U Series Programmable Controllers
User’s Manual - MODBUS Serial Communication Edition
12 Troubleshooting
12.1 Checking the FX3U PLC Version Applicability
11
Practical Program Examples
12
Troubleshooting
12. Troubleshooting
This chapter explains troubleshooting.
12.1 Checking the FX3U PLC Version Applicability
Verify that the FX3U Series PLC main unit is an applicable version.
→ For the version applicability check, refer to Section 1.3.
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.
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.
→ For the wiring check method, refer to Chapter 4.
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.
→ For the MODBUS communication settings, refer to Chapter 5.
LED status
Opeartion status
RD SD
Flashing Flashing Data is being sent and received.
Flashing Off Data is received, but is not sent.
Off Flashing Data is sent, but is not received.
Off Off Data is not sent nor received.