> 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/siemens-s7-write.md). # Siemens S7 Write This function block writes values into a Siemens S7 PLC. It accepts a data input and a client reference, and can perform immediate (synchronous) or scheduled background (asynchronous) writes. An optional value can be provided to be written when the system stops or the block is removed. ## đŸ“Ĩ Inputs `Enable` Provide a boolean to allow or inhibit writes. When not provided or True, writes proceed. `Data` The value to write to the PLC. Accepts the data type selected in the controls. `[Optional] Data on Stop` Optional value that will be written when the block is stopped or removed. `S7 Client` The PLC client/connection reference used to perform the write. (Provide using a connection block such as `Siemens S7 Connect`.) ## 📤 Outputs This function block does not produce outputs. ## 🕹ī¸ Controls `DB Number` Specify the DB number inside the PLC where the value will be written. `DB Byte Address` Specify the byte offset inside the selected DB. `Bit Position` For boolean writes, select the bit position inside the targeted byte. `DB Data Type` Choose the data type to write (for example: boolean, integer, float, string). The block converts the input value according to this selection. `Connection Type` Choose between `Sync` and `Async` modes. `Sync` performs the write immediately and shares a common connection; `Async` schedules the write to run in the background and uses a dedicated connection for this block. ## 🎛ī¸ Key Features * Support for multiple PLC data types with explicit selection via `DB Data Type`. * Byte and bit addressing for precise placement of boolean or scalar values. * Two write modes: * Synchronous (immediate) writes for deterministic single-step operations. * Asynchronous (background) writes to avoid blocking the main flow and to offload longer write operations. * Optional safe-write-on-stop: a value provided to `[Optional] Data on Stop` is written automatically when the block is stopped or removed. * Connection management and reconnection when the client address changes. * Clear error and warning messages to help diagnose connectivity or type issues. ## ⚙ī¸ How it runs * When `Enable` is absent or True, the block attempts to write the value provided on `Data` into the PLC at the configured DB and byte address. * If `Connection Type` is set to `Sync`, the block uses a shared synchronous connection and performs the write immediately. * If `Connection Type` is set to `Async`, the block schedules the write to a background worker so the main flow is not blocked; this uses a dedicated connection instance for the block. * If a client reference on `S7 Client` is not connected, the block will try to (re)connect before attempting the write. * On stop or removal, the block will try to write the value provided to `[Optional] Data on Stop` to ensure a defined final state. ## 📝 Usage Instructions 1. Provide a PLC client reference to `S7 Client` (use `Siemens S7 Connect` to create the connection). 2. Configure target address using `DB Number` and `DB Byte Address`. 3. If writing booleans, set the `Bit Position`. 4. Select the appropriate `DB Data Type` for the data you will write. 5. Choose `Connection Type`: * Use `Sync` when you want immediate writes and share the connection across blocks. * Use `Async` to offload writes to the background and avoid blocking the flow. 6. Feed the value to write into `Data` and enable writing with `Enable`. 7. Optionally provide a value to `[Optional] Data on Stop` to be written when stopping or removing the block. ## 💡 Tips and Tricks * Use `Siemens S7 Connect` to provide a reliable client reference to the `S7 Client` input. * Combine with `Siemens S7 Read` to verify registers before or after writes. * Use `Logic Input` to drive the `Enable` socket from a simple UI toggle. * If you need to prepare or format text/structured data before writing, consider `String Input` or `Data to JSON` upstream. * Use `Data Write Global` / `Data Write Local` or `Data Memory` to store values you intend to write from multiple places in your flow. * For logging or diagnostics, connect a `CSV Export` or `Debug Input` to capture or inspect values you are writing. * Prefer `Sync` mode when multiple blocks write to the same DB/byte to avoid write conflicts; choose `Async` when writes can be handled independently to reduce processing latency. ## 🛠ī¸ Troubleshooting * Lost connection / Write failures: Check the PLC reachability and client provided to `S7 Client`. Use `Siemens S7 Connect` to test the connection separately. * Incorrect data values: Ensure the selected `DB Data Type` matches the actual PLC variable type and adjust `DB Byte Address` / `Bit Position` accordingly. * Server busy or concurrent writes: If you see warnings about the server being busy, try switching to `Sync` mode for shared, serialized writes to the same addresses or ensure each writer uses separate addresses. * Value not written on stop: Make sure a valid value is provided to `[Optional] Data on Stop` and the block is allowed to perform finalization (some shutdown scenarios may prevent final writes). ## ✅ Safety and Best Practices * Double-check DB and byte addresses before writing to live PLCs to avoid unintended changes. * Use write-on-stop carefully; ensure the stop sequence allows the block to complete the final write. * Prefer dedicated connections (`Async`) for heavy or frequent write tasks that should not block the main flow; prefer `Sync` when coordinating writes across multiple blocks.