# Operation Modes

{% hint style="info" %}
See chapters [predefined sequences](/ltt/documentation/ltt-gui-manual/teststand/predefinedsequences.md), [order of execution](/ltt/documentation/ltt-gui-manual/teststand/processmodel/orderofexecution.md) and [process model](/ltt/documentation/ltt-gui-manual/teststand/processmodel.md) for a better understanding.
{% endhint %}

In LTT terminology an **operation mode** is *a sequence of operations, which is executed under certain conditions*. Those conditions can be different voltage levels, temperatures or DUT states (sleep, normal).

A LTT sequence file contains some [predefined sequences](/ltt/documentation/ltt-gui-manual/teststand/predefinedsequences.md), together with various other arbitrary sequences and so called **operation mode sequences**. An operation mode sequence's name need to start with the prefix **OPMODE** or **OM**.

![Operation Modes](/files/4D7UTOMemh4TrXtpT3Gd)

You can think of an operation mode sequence as the **main entry point** for that operation mode. From there on it calls other sequences to do whatever the operation mode should do.

There is, however, a main entry point for the whole LTT sequence file. This entry point is called **MainSequence** and is responsible for **switching to one of the defined operation mode sequences**, depending on the current **temperature chamber contact** state (TCC) and the configuration you made in GUI's [F10 dialog](/ltt/documentation/ltt-gui-manual/lttgui/dialogs/f10testparameterconfiguration.md).

{% hint style="warning" %}
Do not make any changes to the MainSequence.
{% endhint %}

![Operation Mode Cycle](/files/alFShKoNxMLiAUW1mPfs)

The MainSequence will call an operation mode in a continuous cycle, which only exits as a result of a [stop condition](/ltt/documentation/ltt-gui-manual/teststand/processmodel/orderofexecution.md#STOP_CONDITIONS).

{% hint style="warning" %}
If there is no operation mode defined for the current TCC value, the testplan will execute a fallback sequence which does nothing but displaying a status in GUI, that there is no valid operation mode mapping.

<img src="/files/zuuqs52CkxD9cn8voQdA" alt="Invalid OM" data-size="original">
{% endhint %}


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