Underflow Bit
Status bit set when counter goes below zero or math result is too small.
Key Takeaways
- Status bit set when counter goes below zero or math result is too small.
- Intermediate-level topic in Ladder Logic Elements
Detailed Definition
Status bit set when counter goes below zero or math result is too small. This term is essential for understanding ladder logic in industrial automation and PLC programming.
Ladder logic relies on Underflow Bit as part of the small set of primitives that combine into every conceivable PLC program. Status bit set when counter goes below zero or math result is too small.
Underflow Bit is evaluated as part of the PLC's deterministic scan: inputs are sampled, ladder rungs run in sequence, outputs are written, and the process repeats. Underflow Bit sits inside that program-execution phase, where its specific logical or temporal behaviour shapes how the rung resolves.
In a multi-vendor world, Underflow 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.
Common Questions
What is Underflow Bit?
Status bit set when counter goes below zero or math result is too small.
What are related concepts I should learn?
To fully understand Underflow Bit, you should also familiarize yourself with TON (Timer On-Delay), TOF (Timer Off-Delay), and CTU (Count Up). These concepts work together in industrial automation systems.
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Quick Info
- Category
- Ladder Logic Elements
- Difficulty
- Intermediate
- Tier
- Advanced
About Ladder Logic Elements
Contacts, coils, timers, counters, and ladder diagram components