# Operation Modes

URL: https://irs.systems/en/docs/ltt/documentation/ltt-gui-manual/teststand/operationmodes

> See chapters [predefined sequences](/en/docs/ltt/documentation/ltt-gui-manual/teststand/predefinedsequences), [order of execution](/en/docs/ltt/documentation/ltt-gui-manual/teststand/processmodel/orderofexecution) and [process model](../processmodel/) for a better understanding.

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](/en/docs/ltt/documentation/ltt-gui-manual/teststand/predefinedsequences), 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](/docs/assets/ltt/assets/ts-opmodes.png)

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](../../LTTGUI/Dialogs/F10testparameterconfiguration/).

> Do not make any changes to the MainSequence.

![Operation Mode Cycle](/docs/assets/ltt/assets/ts-opmode-cycle.png)

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

> 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="/docs/assets/ltt/assets/station-invalid-om.png" alt="Invalid OM" data-size="original">