# TwinCAT Read This function block reads a variable from a TwinCAT PLC and outputs the retrieved value along with a success indicator. It is intended for simple PLC data retrieval in automation scenarios. ## đŸ“Ĩ Inputs (sockets) `Connection` — Generic PLC connection object (provide using a connect block such as `TwinCAT Connect`). ## 📤 Outputs (sockets) `Data` — Retrieved variable value from the PLC. `Success` — Boolean flag indicating whether the read operation succeeded. ## 🕹ī¸ Controls `Variable Name` — Text field where you enter the PLC variable name to read. This value must match the variable identifier defined in the PLC. ## đŸŽ¯ Features * Simple PLC read operation with clear success feedback. * Designed to accept a connection from a separate connection block, keeping connection management separated from reads. * Validates key inputs and reports clear error messages when connection or variable name is missing. ## 📝 How to use 1. Provide a PLC connection to the `Connection` input. The typical way is to use the `TwinCAT Connect` block and connect its output to this block. 2. Enter the target PLC variable into the `Variable Name` control. 3. Trigger evaluation (manually or from flow controls). The block will attempt to read the named variable and output `Data` and `Success`. 4. Use the `Success` output to gate downstream logic (e.g., logging or storage) so you only act on valid reads. ## 📊 Runtime behavior When evaluated, the block checks that a valid `Connection` is present and that `Variable Name` is not empty. If either is missing it reports an error and outputs a failed `Success`. On a valid configuration it performs a read and outputs the variable value on `Data` and a boolean on `Success`. ## 💡 Tips and Tricks * Use `TwinCAT Connect` to create and manage the PLC connection and feed it into `Connection`. * Combine with `Rising Edge` or `Cycle Timer` to control read frequency (e.g., read once on start or periodically). * Send successful reads to `CSV Export` or `Data to JSON` to log values for later analysis. * Use `Debug Input` or `Scope` to inspect values while you build and test your system. * To write values back to the PLC, pair this block with `TwinCAT Write` and use logic blocks (for example `Logic Input` or `Set - Reset`) to control when reads/writes happen. * Use `Data Write Local` or `Data Write Global` to store values for other parts of your scenario. ## 🛠ī¸ Troubleshooting * If you see "Connection is not established" errors, verify the connection block (for example `TwinCAT Connect`) is configured and connected. * If `Variable Name` is empty, the block will not attempt a read — enter a valid PLC variable identifier. * If a read fails despite valid inputs, check PLC access rights, variable name spelling, and network/PLC status. Use `Debug Input` to capture the raw response and the `Success` output to branch error handling. * If you need periodic stability, control reads with timing blocks like `Cycle Timer` and add simple retry logic using logic blocks. --- # 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.augelab.com/function-blocks/input-output/communication/twincat-read.md?ask= ``` 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.