Logix Add-On Instruction instance and parameter troubleshooting
Trace unexpected AOI behavior through call execution, instance data, parameter direction, InOut references, prescan or enable-state handling, signatures, and imported-definition revisions.
- Product
- Studio 5000 Logix Designer Add-On Instructions
- Level
- Advanced
- Read time
- 16 min
- Reviewed
- 2026-08-13
- Author
- Toolbox editorial team
- Reviewer
- Technical review
What to establish before troubleshooting
An AOI faceplate can show plausible values even when its call is skipped, an InOut argument points elsewhere, or the imported definition differs from the expected revision.
Prove the routine call path and scan mode first, then compare the definition, signature, parameter usage, instance tag, and external arguments without editing a running definition prematurely.
Abbreviated worked example
Example: AOI output remains latched after permissive clears
A reusable equipment AOI stops receiving its normal enable condition, yet one output member remains true in the instance tag.
- 1Prove whether the instruction call still executes and review prescan, enable-in-false, and output handling.
- 2Trace the output parameter and instance member to every external write before changing AOI logic.
Result: The investigation separates retained instance state from a skipped call or competing external write.
Caution: Editing an AOI definition affects every instance and can invalidate a signature; use offline comparison and formal change control.
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