How to | 15 Juli 2020

How to Connect and Use a Siemens S7 Device

Prerequisites

In order to follow along, it would be helpful if you know a bit about:

Service Basics Lesson
Siemens SIMATIC S7 PLCs
Basic computer programming and networking
YAML file format
MQTT

Git URL

Introduction

This lesson goes through the required steps to connect and use your Siemens SIMATIC S7 device with the Cybus Connectware. Following this tutorial will enable you to connect and use your own SIMATIC S7 device on the Connectware with ease!

The SIMATIC S7 is a product line of PLCs by Siemens that are widely used in industrial automation. The S7 is capable of connecting several sensors and actuators through digital or analog IOs which can be modular extended.

The read and write access to data on the PLC can be realized through the S7 Communication Services based on ISO-on-TCP (RFC1006). In this case the PLC acts as a server allowing communication partners to access PLC data without the need of projecting the incoming connections during PLC programming. We will use this feature to access the S7 from the Connectware.

Setup

To follow the lesson you need to have a computer (!), a running Cybus Connectware instance and one of the following

a) A Siemens S7 PLC and access to STEP7 (TIA Portal) The S7 PLC needs to be configured using STEP7 in order to work correctly. The following configuration settings on your S7 device are needed:

To activate the S7 Communication Services you need to enable PUT/GET access in PLC Settings. You should keep in mind that this opens up the controller access by other applications as well.
To access data from data blocks you need to disable “Optimized Block Access” in data block attributes.

b) Conpot PLC Emulator Conpot can be used to emulate a Siemens S7 PLC.

Writing the Commissioning File

The YAML format based Commissioning File tells the Cybus Connectware the type of device to be connected, its connection configuration and specifies the endpoints that should be accessed. Commissioning File details can be found in the Reference docs. For now let’s focus on the three main resources in the file, which are

Cybus::Connection
Cybus::Endpoint
Cybus::Mapping

In the following chapters we will go through the three resources and create an example Commissioning File in which we connect to a S7 device and enable read/write access to a data endpoint.

Cybus::Connection

Inside of the resource section of the commissioning file we describe a connection to a device we want to use. All the information needed for the Connectware to talk to the device is defined here. This information for example includes the protocol to be used, the IP-Address and so on. Our connection resource could look like the following:

# ----------------------------------------------------------------------------#
# Connection Resource - S7 Protocol
# ----------------------------------------------------------------------------#
s7Connection:
  type: Cybus::Connection
  properties:
    protocol: S7
    connection:
      host: 192.168.2.60
      port: 102
      rack: 0
      slot: 1
      pollInterval: 1000

We define that we want to use the Cybus::Connection resource type, which tells the Connectware that we want to create a new device connection. To define what kind of connection we want to use, we are specifying the S7 protocol. In order to be able to establish a connection to the device, we need to specify the connection settings as well. Here we want to connect to our S7 device on the given host IP, port, rack and slot number.

Furthermore, we specified that the pollIntervall for reading the data will be set to one second.

Cybus::Endpoint

We want to access certain data elements on the PLC to either get data from or set data on the device. Similar to the Connection section of the commissioning file, we define an Endpoint section:

# ----------------------------------------------------------------------------#
# Endpoint Resource - S7 Protocol
# ----------------------------------------------------------------------------#
s7EndpointDB1000:
  type: Cybus::Endpoint
  properties:
    protocol: S7
    connection: !ref s7Connection
    subscribe:
      address: DB10,X0.0

We define that we want to introduce a specific endpoint, which represents a data element on the device, by using the Cybus::Endpoint resource. Equally to what we have done in the connection section, we have to define the protocol this endpoint is relying on, namely the S7 protocol. Every endpoint needs a connection it belongs to, so we add a reference to the earlier created connection by using !ref followed by the name of the connection resource. Finally we need to define which access operation we would like to perform on the data element and on which absolute address in memory it is stored at. In this case subscribe is used, which will read the data from the device in the interval defined by the referenced connection resource.

The boolean data element which is addressed here is on a Datablock Byte 0 Bit 0, you can learn more about addressing here.

Cybus::Mapping

Now that we can access our data-points on the S7 device we want to map them to a meaningful MQTT topic. Therefore we will use the mapping resource. Here is an example:

# ----------------------------------------------------------------------------#
# Mapping Resource - S7 Protocol
# ----------------------------------------------------------------------------#
mapping:
  type: Cybus::Mapping
  properties:
    mappings:
      - subscribe:
          endpoint: !ref s7EndpointDB1000
        publish:
          topic: !sub '${Cybus::MqttRoot}/DB1000'

Our example mapping transfers the data from the endpoint to a specified MQTT topic. The important part is where we define from which source we want the data to be transferred to which target. The source is defined by using subscribe and setting the endpoint to reference the endpoint from the endpoints section above. The target is defined by using publish and setting the topic to what MQTT topic we want the data to be published on. In this example we are using !sub which is similar to !ref but substitutes values from somewhere else as a string replacement.

Interim summary

Adding up the three previous sections, a full commissioning file would look like this:

---
description: >
  S7 Example

metadata:
  name: "S7 Device"

resources:
# ----------------------------------------------------------------------------#
# Connection Resource - S7 Protocol
# ----------------------------------------------------------------------------#
  s7Connection:
    type: Cybus::Connection
    properties:
      protocol: S7
      connection:
        host: 192.168.2.60
        port: 102
        rack: 0
        slot: 1
        pollInterval: 1000

# ----------------------------------------------------------------------------#
# Endpoint Resource - S7 Protocol
# ----------------------------------------------------------------------------#
  s7EndpointDB1000:
    type: Cybus::Endpoint
    properties:
      protocol: S7
      connection: !ref s7Connection
      subscribe:
        address: DB10,X0.0

# ----------------------------------------------------------------------------#
# Mapping Resource - S7 Protocol
# ----------------------------------------------------------------------------#
  mapping:
    type: Cybus::Mapping
    properties:
      mappings:
        - subscribe:
            endpoint: !ref s7EndpointDB1000
          publish:
            topic: !sub '${Cybus::MqttRoot}/DB1000'

Writing Data

Usually we also want to write data to the device. This can easily be accomplished by defining another endpoint where we use write instead of subscribe.

s7EndpointDB1000Write:
  type: Cybus::Endpoint
  properties:
    protocol: S7
    connection: !ref s7Connection
    write:
      address: DB10,X0.0

We also append our mappings to transfer any data from a specific topic to the endpoint we just defined.

mapping:
  type: Cybus::Mapping
  properties:
    mappings:
      - subscribe:
          endpoint: !ref s7EndpointDB1000
        publish:
          topic: !sub '${Cybus::MqttRoot}/DB1000'
      - subscribe:
          topic: !sub '${Cybus::MqttRoot}/DB1000/set'
        publish:
          endpoint: !ref s7EndpointDB1000Write

To actually write a value, we just have to publish it on the given topic. In our case the topic would be services/s7device/DB1000/set and the message has to look like this:

{
  "value": true
}

Commission the device on the Connectware

We are finally ready to connect to our Siemens S7 PLC and use it! Go to the Services tab in the Connectware, click on the (+) button in the upper right corner and choose the Commissioning File that we just created.

In case you used parameters in the file, you will be prompted now to fill those in.

If you are ready, press Install and the service will be installed. The status section indicates the health of the service and the resources it defines.

Once the service is installed it needs to be enabled. Therefor click on the service and press ENABLE in the top, right corner.

You will be prompted to authorize all permissions the service needs to operate. After going through all of them, click on ALLOW to enable the service.

If everything went well, the service should change its status to ENABLED (green).

To see the incoming data go to the Explorer Tab in the Connectware and see the MQTT topic we specified in the Commissioning Files.

To watch data flowing simply go to the Explorer Tab and activate watching for the topics we are interested in. To see the value change just publish a value like described in the Writing Data section.

Summary

In this Cybus Learn article we learned how to connect and use a S7 device on the Connectware. See Example Project Repo for the complete Commissioning File. If you want to keep going and get started with connecting your own S7 device with custom addressing, please visit the Reference docs to get to know all the Connectware S7 protocol features.

Going further

A good point to go further from here is the Service Basics Lesson, it covers how to use the data from your S7 device.

Disclaimer:
Step7, TIA Portal, S7, S7-1200, Sinamics are trademarks of Siemens AG

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