AFI (Always False)

Instruction that always evaluates false, used to disable rungs during testing. This term is essential for understanding ladder logic in industrial automation and PLC programming.

AFI (Always False) is part of the visual vocabulary of ladder logic, the relay-derived language that virtually every PLC vendor still supports. Instruction that always evaluates false, used to disable rungs during testing.

AFI (Always False) 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. AFI (Always False) sits inside that program-execution phase, where its specific logical or temporal behaviour shapes how the rung resolves.

For ladder programmers, AFI (Always False) is one of the components you reach for instinctively after enough rungs. The visual nature of ladder makes it readable to electricians and operators in a way that text-based languages aren't, which matters in environments where maintenance happens at 2 AM by whoever is on call.