IEC 61131-3 Programming Languages Reference Overview IEC 61131-3 defines 5 programming languages for PLCs, all interchangeable: | Language | Type | Best For | Status | |----------|------|----------|--------| | LD (Ladder Diagram) | Graphical | Discrete logic, motor interlocks | Active | | FBD (Function Block Diagram) | Graphical | Continuous control, PID, analog | Active (DCS primary) | | ST (Structured Text) | Textual | Complex calculations, algorithms | Active (most expressive) | | IL (Instruction List) | Textual | Low-level, assembly-like | Deprecated (3rd ed. 2013) | | SFC (Sequential Fun…