Control Expert supports the five IEC 61131-3 languages shown here: Ladder, Function Block Diagram, Structured Text, Instruction List and SFC. The motor example compares their representations of a start, seal-in and stop sequence. Operate the inputs, then switch views to connect each contact, expression or step with the resulting motor state.
The logic: press Start, the motor runs and seals in; press Stop and the motor stops. Switch between Ladder, FBD, Structured Text, Instruction List and SFC to inspect the same intended control behaviour. The shared simulation drives each view; it does not compile the displayed vendor code or establish that the generated instructions would be identical.
Motor := (Start OR Motor) AND NOT Stop; // reads like the sentence: run if Start // or already-running, unless Stop is pressed
LD Start OR Motor ANDN Stop ST Motor // the same logic as raw stack instructions — // the assembly language of PLCs (legacy)
Turn Start on and then off. The motor remains on because the seal-in holds its running request until Stop is applied. The SFC view represents the sequence as S1 Idle → (Start) → S2 Run → (Stop) → back. Steps show the active stage, and transitions state the condition for moving to the next stage. That makes SFC useful when the machine's operation is organized into a sequence.
Select a language to read its description, then compare the way it expresses the motor example. The useful choice depends on the logic you need to read and maintain.
A bottling machine follows fill → wait → cap → wait → eject, with a defined condition between stages. Which representation makes those stages and their transitions explicit?