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Learn how to efficiently write integer values to your PLC using Python's Snap7 library. Step-by-step guidance with code examples included.
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How to Write Data to int Value in PLC Using Python and Snap7

When working with Programmable Logic Controllers (PLCs), it's crucial to be able to read and write data effectively, especially if you're interfacing with them using Python. One common task is modifying integer values stored in a PLC's data block. This post will guide you through the steps required to perform this operation using the Snap7 library in Python.

The Problem: Writing Integer Values to PLC

If you're using Snap7 to interact with a Siemens PLC, you may have encountered a situation where you needed to change an integer value that you've previously read from a data block. You already have the code to read the data, but how do you write back an updated integer value? Let’s break it down.

The Solution: Writing Data Back to PLC

To modify an integer value in a PLC using the Snap7 library, you will follow a straightforward process. Here’s how you can achieve this step-by-step:

Step 1: Modify Your Integer Value

First, you need to change the integer value in your byte array. To do this, you will utilize the set_int() function from the Snap7 utility. Here’s a brief code snippet:

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Detail: This code sets the integer value your_int_value starting from the byte with index 256 in the byte array db which you previously read from the PLC.

Step 2: Write the Modified Byte Array Back to PLC

Once you have your byte array updated, you will need to send it back to the PLC. This is done using the db_write() method from the Snap7 client. Here’s how you can do that:

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Detail: This command writes the byte array db to the specified data block (data_blok) starting from the byte at start_address.

Complete Example

To put it all together, here's a complete example that includes modifying and writing different data types back to the PLC:

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Additional Functions for Writing Specific Data Types

You may want to write other data types as well. Here’s how you can create functions for writing boolean, byte, integer, and real values:

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Conclusion

By following the steps outlined in this post, you can easily write integer values back to your PLC using Python and the Snap7 library. Whether you need to update a single integer or manage more complex data structures, these concepts will help you streamline your workflow. Happy coding!