> 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-documentation/5-logic-and-layers-dynamic/logic-layer.md). # Logic layer ## Model the sequence The **logic layer** describes the **logical sequence of a sequence**.\ It models **states and transitions**, however **no technology** and **no signals**. The goal of the logic layer is to describe the sequence: * understandably * unambiguously * deterministically to describe. > **The logic layer answers the question:**\ > **In which logical situation is the process –**\ > **and how does it continue?** *** ### Basic principle of the logic layer In the logic layer applies: * a sequence is always in **exactly one state** * transitions only occur when conditions are met * states describe **situations**, not actions * technology is **not** described in the logic layer The logic layer is therefore: * independent of hardware * independent of PLC * completely process-logical *** ### state #### meaning A **state** describes a **logical situation** in the sequence. Examples: * *workpiece inserted* * *clamping established* * *processing completed* A state: * contains no commands * contains no actuator movements * only defines, **when it is considered fulfilled** > **A state describes, *****that***** something is the case –**\ > **not, *****how***** it is brought about.** *** #### When a state makes sense * when a clear process situation exists * when several conditions must be met together * when the state can be named unambiguously #### When a state does not make sense * for short technical intermediate actions * for pure actuator movements * for PLC-internal auxiliary states *** ### timer state #### meaning A **timer state** is a state with **a temporal condition**. It is considered fulfilled: * when the underlying state is active * and a defined time has elapsed Examples: * hold time after clamping * waiting time before a check step * cooling time *** #### When a timer state makes sense * when time is part of the process * when time logically belongs to the state * when the sequence must be reproducible in a time-dependent way #### When a timer state does not make sense * to compensate for unstable technology * as a substitute for missing feedback * for purely technical delays *** ### decision #### meaning A **decision** describes a **logical branching** in the sequence. It decides: * which subsequent path is taken * based on clear conditions Examples: * test result OK / NOK * option activated / not activated * repeat / continue *** #### When a decision makes sense * when the process has multiple logical paths * when the decision is technically justified * when the decision must be explicitly traceable #### When a decision does not make sense * to map technical boundary conditions * for error compensation * as a substitute for clean state definitions *** ### repeater #### meaning A **repeater** repeats one or more states. It is used to: * loops * repetitions * test cycles formally map. Examples: * multiple testing * retry attempts * iterative processing step *** #### When a repeater makes sense * when repetition is part of the process * when number or condition is defined * when the sequence should remain structured #### When a repeater does not make sense * for uncontrolled endless loops * to compensate for unstable processes * when repetition is not technically justified *** ### jump #### meaning A **jump** consciously leaves the linear sequence\ and jumps to another state. There are: * conditional jumps * unconditional jumps Examples: * abort paths * targeted backward jumps * exception handling *** #### When a jump makes sense * for clearly defined special cases * for abort or reset paths * when the sequence would otherwise become confusing #### When a jump does not make sense * as a substitute for clean structure * for normal sequence * to circumvent modeling errors > **Jumps are powerful – and should be used sparingly.** *** ### sequence cross #### meaning **sequence cross** connects **multiple sequences logically with each other**. It enables: * synchronization * dependencies between sequences * coordinated transitions Examples: * robot waits for station * station waits for transport * parallel processes with synchronization point *** #### When sequence cross makes sense * in modular plants * with parallel sequences * when sequences should remain logically separate #### When sequence cross does not make sense * for artificial splitting of simple sequences * with unnecessary fragmentation * when one sequence would be logically sufficient *** ### important distinction The logic layer: * describes **not** * signals * actuators * safety logic * operation These aspects belong: * in the **system layer** * in **zones** * in **bit control** * in **CMZ / MXIC** > **The logic layer describes the sequence –**\ > **not its technical implementation.** *** ### summary The logic layer: * is the logical backbone of every sequence * describes the sequence in states * separates process logic from technology * enforces clarity and determinism The logic elements are tools –\ their quality is shown in the **conscious use**. > **A good logic layer is simple,**\ > **explainable and free of technical details.** --- # Agent Instructions This documentation is published with GitBook. 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