> 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/modbus-write.md). # Modbus Write This function block sends values to a Modbus server using a provided Modbus client. Use it to write coils or holding registers from your scenario graph. ## đŸ“Ĩ Inputs `Enable` This boolean input controls whether writing is performed. If not provided or False, the block will not attempt to write. `Modbus Client` This input expects a client object produced by the `Modbus Connect` block. Provide a valid client to enable communication. `Data` Generic data to write. Accepts a single value or a list (for writing multiple coils/registers). ## 📤 Outputs This function block produces no outputs. ## 🕹ī¸ Controls `Address` Enter the Modbus register/coils address to write to. Use integer values that match your device map. `Data Type` Choose between `Coil` and `Holding Register` to select which Modbus resource type will be written. ## đŸŽ¯ Features * Supports writing single values or lists to multiple addresses when the device supports it. * Lets you choose the target resource type with a simple dropdown: `Coil` or `Holding Register`. * Respects the `Enable` input so writing can be controlled from logic or user inputs. * Reports errors to the log if writing fails so you can diagnose connection or configuration problems. ## ⚙ī¸ Running mechanism When the block runs: * If the `Enable` input is False or missing, no write is attempted. * If no client is provided at `Modbus Client`, the block will not perform any write. * When enabled with a valid client, the block sends the supplied `Data` to the address entered in `Address` using the selected `Data Type`. * Errors (connection problems, invalid address, unsupported data) are reported to the log so you can act accordingly. ## 📝 Usage instructions * Add a `Modbus Connect` block and connect its `Modbus Client` output to this block's `Modbus Client` input. * Set `Address` to the register or coil address you want to write. * Select `Data Type` as `Coil` for boolean/coils or `Holding Register` for numeric registers. * Feed your data into the `Data` input (single value or list). * Use a `Logic Input` or other control to toggle `Enable` when you want the write to occur. ## 💡 Tips and Tricks * Use `Modbus Connect` to produce a reliable client and confirm the connection with `Modbus Read` before trying to write. * Drive the `Enable` input from a `Logic Input` or a conditional block (for example `Equals` / `Greater`) so writes occur only under desired conditions. * Prepare write values using `Number Input` or by assembling data with blocks like `String Merge` or `Data Write Global` / `Data Write Local` when you need to stage values. * If you need to save or export values you write, combine this block with `CSV Export` or `REST API - Post` to keep external logs or send notifications. ## 🛠ī¸ Troubleshooting * No write happening: check that the `Enable` input is True and that a valid `Modbus Client` is connected. * Invalid address errors: ensure `Address` is an integer within the device address map and matches the chosen `Data Type`. * Unexpected data format: for `Coil` use boolean or list of booleans; for `Holding Register` use numbers or a list of numbers. * Write failures: verify connectivity with `Modbus Read` and confirm the server accepts writes to the target address. Check log messages for details.