# Predefined Sequences

A LTT testplan need to have certain predefined sequences.

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

![Standard Sequences 1](/files/7aqJjPswNmsF7nCA36ec)

The green and purple sequences at the top are predefined **mandatory** TestStand sequence callbacks triggered by the process model. They will be triggered in the following order.

1. **SequenceFileLoad**: called at sequence file load. Initializes limits.
2. **ProcessSetup**: called one time after start for all stations. Use this to perform initializations per LTT and not per DUT.
3. **PreUUTLoop**: called one time after start for each DUT.
4. **MainSequence**: main sequence entry point. Do not make any changes here. It serves as a dispatcher to the various [operation mode sequences](/ltt/documentation/ltt-gui-manual/teststand/operationmodes.md).
5. **PostUUTLoop**: called one time during stop for each DUT.
6. **ProcessCleanup**: called one time during stop for all stations. Use this to perform cleanup per LTT and not per DUT.

![Standard Sequences 2](/files/DiXvNt5B4oQhzgdAv6un)

Additionally to the standard TestStand sequence callbacks there are a couple of other, **optional** sequences.

| Sequence              | Outcome                                                                                                                  |
| --------------------- | ------------------------------------------------------------------------------------------------------------------------ |
| Sync                  | Synchronizes the execution of all stations at this point. Optionally sets the power supply to a different voltage level. |
| MesSy Setup           | Performs the MesSy setup.                                                                                                |
| MesSy Analog Config   | Configures MesSy analog channels (scaling, offset).                                                                      |
| MesSy Activate Limits | Activates a given limit set on MesSy.                                                                                    |
| MesSy SSV Check       | Performs a SSV check on a given limit set.                                                                               |
| MesSy Clear Errors    | Clears any previous SSV check results.                                                                                   |

Besides those standard and optional sequences above, there are so called [operation mode sequences](/ltt/documentation/ltt-gui-manual/teststand/operationmodes.md), which are important for the LTT.

{% hint style="info" %}
A LTT testplan need to contain at least one operation mode sequence.
{% endhint %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.irs.systems/ltt/documentation/ltt-gui-manual/teststand/predefinedsequences.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.