> For the complete documentation index, see [llms.txt](https://infosys.selmotech.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://infosys.selmotech.com/selmo-solution/selmo-solution-en/selmo-how-it-works/selmo-training/chapter-1-the-theoretical-background/1.5-the-difference-to-classical-plc-programming.md).

# 1.5 The difference to classical PLC programming

Classical PLC programs are **imperative**:\
they consist of instructions that are executed step by step.\
Selmo programs are **declarative**:\
they describe, *what* should hold, not *how* it is executed.

An example:\
In a conventional PLC program it would say:

IF StartButton = TRUE THEN
\
Cylinder1Extend := TRUE;
\
IF FrontSensor = TRUE THEN
\
NextStep := 2;
\
END\_IF;
\
END\_IF;

In Selmo the description instead reads:

* State 1: “Waiting for start button” → Button (IN zone) has operand S.
* State 2: “Extend cylinder 1” → Cylinder 1 (IN\_OUT zone) has operand S.
* If feedback = TRUE, the state machine automatically moves to the next state.

No code, no nested logic, no misinterpretation – the sequence is described by the model itself.


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