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PROGRAMMING • FX5U / GX WORKS3

Why did an FX5U value change after power loss?

Check whether the device range is configured as latched/retentive and whether the project parameters currently in the CPU match the offline project.

Practical explanation

Retention behavior is determined by the CPU/device configuration and application design.

Critical recipes should also have validation, limits and a deliberate initialization strategy.

Check in this order

  1. 1Read the current PLC parameters.
  2. 2Review latch ranges and initialization logic.
  3. 3Test a controlled power cycle.
  4. 4Confirm the value is not overwritten on first scan.

Last reviewed: 2 October 2026

Official source: MELSEC iQ-F FX5 User's Manual (Application)

Related verified answers

What should be initialized on the first PLC scan?

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