> 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-structure-and-standard/selmo-technical-standard-and-structure/layer-overview/layer-concept.md).

# Layer concept

### 📘 The layer concept in Selmo

The Selmo system is structured in three layers – in so-called **layers**.\
Each layer fulfills a clearly defined function:

* **Logic Layer** – describes the sequence
* **System Layer** – defines the behavior of the signals
* **Parameter layer** – manages data such as times, counters, values

This separation creates transparency, verifiability and reusability – from the model to code generation.

***

#### 🔷 1. Logic Layer – the sequence plan

The Logic Layer is the centerpiece of the model. Here the **process is described in states**.

| element          | Function                                        |
| ---------------- | ----------------------------------------------- |
| `State`          | normal state (e.g. “clamp part”)                |
| `Timer`          | automatically continue after a defined time     |
| `Decision`       | conditional branching (e.g. sensor ok?)         |
| `Repeater`       | repetition loops (e.g. “up to max. 3 attempts”) |
| `Jump`           | jump to another state (e.g. in case of error)   |
| `Sequence cross` | synchronous transition to another SEQ           |

**The Logic Layer forms the deterministic automaton (SDEA)** – i.e. a fully describable sequence, free of side effects.

***

#### 🔷 2. System Layer – bit control & zone behavior

The System Layer determines **how each zone should behave in each state**.\
It consists of a matrix (bit control) in which:

* the rows are states,
* the columns are zones,
* and each cell position contains an **operand** carries:

| Operant | Meaning                                            |
| ------- | -------------------------------------------------- |
| `0`     | Zone is inactive in this state                     |
| `S`     | sequence check – zone is actively expected         |
| `i`     | interlock – zone must be fulfilled, otherwise stop |

Additionally, the following are:

* HMI texts
* colors
* safety linkages (CMZ, MXIC)\
  are automatically generated from the System Layer.

***

#### 🔷 3. Parameter Layer – data logic

The Parameter Layer allows **non-binary values** to be integrated into the model – e.g.:

* times (`TIME`)
* counters (`INT`)
* flags (`BOOL`)
* positions (`REAL`)

Each parameter can be used as:

| direction | Function                                     |
| --------- | -------------------------------------------- |
| `IN`      | adjustable by the operator (e.g. cycle time) |
| `OUT`     | determined by the system (e.g. actual time)  |
| `IN/OUT`  | combinable (e.g. teachable setpoints)        |

Parameters can:

* be used in states (e.g. timer time)
* be displayed or modified in the HMI
* communicate via OPC UA or MES interfaces

***

#### 🎯 Advantages of layer separation

| Advantage       | Meaning                                                    |
| --------------- | ---------------------------------------------------------- |
| **Clarity**     | Each function has its defined level                        |
| **maintenance** | Changes affect only the affected layer                     |
| **export**      | Each level produces its own documentation                  |
| **Modularity**  | Layers can be reused between projects                      |
| **Validation**  | Logic, signal behavior and data checking clearly separated |

***

### ✅ Conclusion

The layer concept makes Selmo **clean, maintainable, extendable and traceable**.

📌 *Logic → defines the sequence*,\
📌 *System → secures the behavior of the technology*,\
📌 *Parameter → provides values for variability, performance and interface.*


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