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Connecting Siemens PLCs Using the S7 Protocol with reComputer R1000

Introduction​

The S7 Protocol is a communication standard developed by Siemens for their family of programmable logic controllers (PLCs). It's crucial for enabling smooth and reliable data exchange between Siemens PLCs. This protocol operates over Ethernet using a method called ISO TCP, which is structured around blocks of data known as Protocol Data Units (PDUs). Each PDU is a segment of information whose size and structure are determined when the connection is first established.

In this article, we'll explore how to use Node-RED, a popular flow-based development tool, on a Raspberry Pi-powered reComputer to interface with Siemens PLCs using the S7 Protocol. This setup allows for efficient and flexible integration of industrial automation systems with modern IoT platforms.

Configuring Your PLC for S7 Protocol​

After designing your Ladder or Function Block Diagram, the next step is to configure your Siemens PLC to enable the S7 protocol. The exact steps may vary depending on the PLC model you're using. For example, if you’re using a Siemens LOGO PLC, you’ll configure this in the LOGO Soft programming software.

Network Configuration: Under the Ethernet settings, you'll need to input the PLC's IP address, subnet mask, and default gateway.

Enable S7 Protocol: There’s an option to allow S7 communication—make sure to tick this box.

Set Up S7 Communication: Add an Ethernet connection configured as an S7 server. You’ll also need to set up the Client and Server TSAP (Transport Service Access Point).

note

If you’re using a different Siemens PLC model, be sure to consult the relevant documentation for specific configuration steps.

Configuring S7 Nodes in Node-RED​

To integrate Siemens PLCs with Node-RED, you'll need to use the node-red-contrib-s7 node. Follow these steps to set it up:

Install the S7 Node​

  • Go to the Manage Palette option in Node-RED.
  • Navigate to the Install tab and search for node-red-contrib-s7.
  • Install the node to add S7 capabilities to your Node-RED environment.

Create a Flow​

  • Drag and drop the S7 out node onto your workspace, along with two inject nodes.
  • Connect the inject nodes to the S7 out node to initiate communication with the PLC.

Configure the S7 Out Node​

  • First, configure the endpoint by clicking the + (plus) icon.
  • Enter the IP address of your PLC.
  • Set the Mode to TSAP.
  • Input the Local TSAP and Remote TSAP as configured in your PLC’s server settings.
  • Give your PLC a recognizable name for easy identification.

Add Variables​

  • Define each variable with a Name and Address.
  • Use the appropriate address spaces corresponding to different block types (e.g., coils, inputs). You can refer to Siemens S7 Address Documentation for more details.
  • Ensure each variable name accurately corresponds to its block type.

Configure the Inject Node​

  • Edit the inject node’s payload to set a boolean value. Use one inject node for true and another for false.

Add S7 In Node for Monitoring​

  • Drag and drop the S7 in node to monitor variable values.
  • You can configure this node to view a single variable or all variables.
  • Select the corresponding PLC, Mode, and Variable you wish to monitor.

Deploy Your Flow​

  • Once everything is configured, deploy your flow to start communicating with your Siemens PLC.

Tech Support & Product Discussion​

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