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GX WORKS3 • FX5U / GX WORKS3

Should I read the PLC program before making an FX5U change?

Yes. Read and save a dated backup of the running PLC before editing, then compare it with the project you intend to change.

Practical explanation

An offline file may not match the program currently controlling the machine.

Include parameters, labels/comments and other required data in the backup where available.

Check in this order

  1. 1Confirm the machine and CPU identity.
  2. 2Read from PLC and save with date and revision.
  3. 3Compile the edited project.
  4. 4Write only the intended data and verify afterward.

Safety: Obtain machine authorization and put equipment in a safe state before online changes.

Last reviewed: 2 October 2026

Official source: GX Works3 Operating Manual

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