Overflow Bit

Status bit set when counter or math operation exceeds maximum value. This term is essential for understanding ladder logic in industrial automation and PLC programming.

In ladder logic — the most widely used PLC programming language and the foundation that the IEC 61131-3 standard formalises — Overflow Bit is one of the building blocks that turns electrical-engineering reasoning into executable PLC code. Status bit set when counter or math operation exceeds maximum value.

Inside the scan cycle, Overflow Bit is processed during the program execution step. Its behaviour is deterministic — given the same inputs, it always produces the same outputs in the same time — which is exactly what industrial control demands.

In a multi-vendor world, Overflow Bit appears with subtle syntactic differences across Siemens TIA Portal, Rockwell Studio 5000, Mitsubishi GX Works, and Codesys-based IDEs — the IEC 61131-3 standard governs the concept, but vendors layer their own conventions on top.