Siemens S7 Write

This function block writes data to a Siemens S7 PLC (Data Block). Use it to send numbers, booleans, strings and other supported types into a PLC address directly from your scenario.

📥 Inputs

Enable Provide TRUE to allow writing. If FALSE or empty no write will occur.

Data The value to write to the PLC. Accepts numeric, boolean, text or complex data depending on the selected DB Data Type.

[Optional] Data on Stop If provided, this value will be written once when the scenario or block is stopped/removed.

S7 Client Provide a connection reference from a connection block (for example Siemens S7 Connect) so the block can reach the PLC.

📤 Outputs

This function block does not produce outputs.

🕹️ Controls

DB Number Data Block number to write into on the PLC.

DB Byte Address Starting byte address inside the chosen DB where the value will be written.

Bit Position Use this only for boolean writes to select which bit inside the target byte should be set.

DB Data Type Choose the data type to write (examples: Boolean, Int, Real, String, Time, etc.). The choice controls how the input value is encoded on the PLC side.

Connection Type Choose Async or Sync. Async schedules the write to a background worker; Sync performs the write immediately.

🎯 Features

• Write a wide range of PLC data types including numerical types, booleans, and strings.

• Optional "write on stop" value that will be pushed to the PLC when the block or scenario is stopped.

• Two connection modes: synchronous immediate write and asynchronous background write to avoid blocking the main flow.

• Automatic reconnection support when the provided client address changes (useful when reorganizing connections).

• Simple UI controls for DB, byte address and bit position — no coding required.

⚙️ Running Mechanism

• When Enable is TRUE and a valid S7 Client is provided, the block attempts to write the Data to the selected DB and byte address using the chosen DB Data Type.

• If Connection Type is set to Async, the write is scheduled to run in a background worker so the main scenario can continue without delay.

• If Connection Type is set to Sync, the block performs the write as part of the current execution step.

• If a value is provided in [Optional] Data on Stop, that value will be written automatically when the block is stopped or removed.

• The block logs informative messages on success, warnings when the PLC/client is busy, and errors when writes fail or parameters are invalid.

📝 Usage Instructions

1. Add a connection block such as Siemens S7 Connect and configure the PLC address.

2. Feed that connection into the S7 Client input of this block.

3. Set the DB Number, DB Byte Address, and, if writing a boolean, the Bit Position.

4. Select the proper DB Data Type for the value you will write.

5. Choose Connection Type:

   • Use Sync for immediate writes or when few writes are performed.

   • Use Async to offload frequent or slow writes to a background worker.

6. Provide a value to the Data input (for manual input you can use blocks like Number Input or String Input).

7. Enable the block by providing TRUE to Enable to perform the write.

8. Optionally provide a value to [Optional] Data on Stop to be written when the block is stopped.

💡 Tips and Tricks

• Use Siemens S7 Connect together with this block to manage the PLC connection and provide the S7 Client input.

• After writing, verify values with Siemens S7 Read to confirm the expected DB contents.

• For manual triggers, combine with Logic Input or Number Input to control when writes occur.

• When writing textual values, feed text from String Input so encoding matches expectations.

• If you need to store values for later use or coordinate multiple blocks, consider combining with Data Write Local / Data Read Local or Data Write Global / Data Read Global.

• Use Debug Input to log or inspect values before sending them to the PLC.

• Prefer Sync mode when multiple blocks must write to the same exact bytes — it reduces race conditions. Use Async for higher throughput when writes are independent.

🛠️ Troubleshooting

• Connection errors or "cannot write" messages:

  • Confirm the S7 Client input is connected and the connection block is configured with the correct PLC address and active.

  • Try re-establishing the connection from the connection block.

• Wrong values seen on PLC:

  • Verify DB Number, DB Byte Address and Bit Position are correct for the target variable.

  • Ensure the selected DB Data Type matches the PLC variable type (e.g., writing a float with an integer type will produce incorrect values).

• String writes truncated or corrupted:

  • Check the PLC side expects a length byte or fixed-size buffer. Limit string length accordingly.

• Writes are too slow or block the scenario:

  • Switch Connection Type to Async so writes occur in the background.

• Multiple writers to same address cause conflicts:

  • Use Sync mode for blocks writing to the same DB/bytes, or centralize writes using a single dedicated writer block.

If problems persist, re-check address mapping on the PLC and validate with a read operation (for example using Siemens S7 Read) before relying on subsequent writes.