> For the complete documentation index, see [llms.txt](https://docs.augelab.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.augelab.com/function-blocks/blocks-reference/input-output/communication/twincat-write.md).

# TwinCAT Write

This function block writes a value to a TwinCAT PLC variable using an existing PLC connection. Use it to push numeric, boolean or textual values from your scenario into the PLC and receive a simple success indicator.

## 📥 Inputs <a href="#inputs" id="inputs"></a>

* `Connection` — PLC connection object (provide from a communication setup block such as TwinCAT Connect).
* `Value` — The value to be written into the PLC variable (number, text, boolean, or structured value depending on your PLC variable).

## 📤 Outputs <a href="#outputs" id="outputs"></a>

* `Success` — Boolean indicating whether the write operation succeeded.

## 🕹️ Controls <a href="#controls" id="controls"></a>

* `Variable Name` — Enter the exact PLC variable name/address you want to write to (as defined in your TwinCAT project).

## ⚙️ Running mechanism <a href="#running-mechanism" id="running-mechanism"></a>

When this block runs it:

1. Reads the provided `Connection` and `Value` inputs and the `Variable Name` control.
2. Validates that a variable name, a valid connection, and a value are present.
3. Attempts to write the provided value into the specified PLC variable via the supplied connection.
4. Emits `Success` as True when the write completes, otherwise False and logs an error message for troubleshooting.

## 🎯 Features <a href="#features" id="features"></a>

* Simple single-variable write operation with a clear single boolean result.
* Input-flexible: accepts generic values so it can be used with numeric, textual and boolean data sources.
* Error reporting: informs you when connection, variable name or value is missing or when a write fails.

## 📝 Usage instructions <a href="#usage" id="usage"></a>

1. Add a PLC connection block such as TwinCAT Connect and configure it.
2. Feed the connection output into the `Connection` input of this block.
3. Provide a value to write using a suitable input block (for example a Number Input or String Input) into the `Value` input.
4. Enter the PLC variable name in the `Variable Name` control.
5. Run the scenario and check the `Success` output to confirm the write.

## 💡 Tips and Tricks <a href="#tips-and-tricks" id="tips-and-tricks"></a>

* Use `TwinCAT Connect` to create and supply the `Connection` input.
* Use `Number Input`, `String Input` or `Logic Input` to prepare the `Value` input depending on the variable type in the PLC.
* After writing, verify the result by reading the same variable with `TwinCAT Read`.
* If your value type is unclear, pass the data through `Data Type Converter` before writing to ensure type compatibility.
* Add a `Debug Input` or `Is None` check upstream to detect missing or invalid values and avoid failed writes.
* Log successful writes or failures using CSV Export or MQTT Publish for audit trails or remote monitoring.

## 🛠️ Troubleshooting <a href="#troubleshooting" id="troubleshooting"></a>

* If `Success` is False: verify the `Variable Name` is exactly as defined in the PLC (including namespaces/paths).
* Ensure the provided `Connection` is active and correctly configured (check TwinCAT Connect status).
* Confirm the value type matches the PLC variable type; convert types upstream if necessary.
* Check logs shown by the block for descriptive error messages to guide corrective actions.