PLC / PLC Programming, Timing & State Logic
Investigate a PLC runtime exception near indexed data access
An index can exceed a declared array range because of unexpected input, sequence state or a changed dataset.
Environment and inputs: Industrial PLC / automation guidance · Verify the exact controller, module, firmware, engineering tool and machine documentation. Linked vendor examples apply to their stated products and library versions; observation, state changes and physical work require distinct authorization.
Observe and record
Preserve fault location and approved sanitized index and bound information from available diagnostics or an offline reproduction.
Interpret the evidence
Out-of-range behavior and runtime checks differ by platform. A nearby array access is evidence to investigate, not proof of a faulty CPU.
Resolve and verify
Correct the demonstrated indexing and validation logic, then test minimum, maximum and invalid inputs before deployment.
Machine and data safeguards
Do not disable runtime checks or clamp an index blindly when doing so could select the wrong machine parameter.