← Verified Knowledge Base Source checked

PROGRAMMING • FX5U / GX WORKS3

What should be initialized on the first PLC scan?

Initialize only values that must return to a known startup state. Do not overwrite retained production data, calibration or recipes unless that is the documented requirement.

Practical explanation

Startup logic should make machine state predictable while preserving values that operators expect to survive a power interruption.

A startup command must never cause unintended motion.

Check in this order

  1. 1List retained and non-retained data separately.
  2. 2Reset transient sequence flags.
  3. 3Validate recipes before use.
  4. 4Require normal safety and start conditions for motion.

Safety: Keep outputs de-energized until safety, mode and machine-state checks are valid.

Last reviewed: 2 October 2026

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

Related verified answers

Why did an FX5U value change after power loss?

Still need help with your machine?

Ask a real question in the community and include the PLC model, software version, error and what you already checked.

Ask the community