Connect a PLC Device

Shifu is compatible with the Siemens S7 series. Shifu can be used to modify the memory of an S7 PLC via HTTP requests. This article will show how to access a Siemens S7-1200 1214C PLC and interact with it.

Connection

Step 1

Before connecting to Shifu, the PLC should have a physical connection to the host machine of Shifu through the Ethernet and own an IP address. We use 192.168.0.1 here as the IP address. (If the IP address of your PLC device is not 192.168.0.1, you can change PLC_ADDRESS in deviceshifu-plc-deployment.yaml to the IP address of your device.)

Step 2

Create a folder named plc_configuration_directory and create the following four configuration files in this folder.

First, a configuration is required to access the IP address and device type:

Click here to view deviceshifu-plc-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: deviceshifu-plc-deployment
  name: deviceshifu-plc-deployment
  namespace: deviceshifu
spec:
  replicas: 1
  selector:
    matchLabels:
      app: deviceshifu-plc-deployment
  template:
    metadata:
      labels:
        app: deviceshifu-plc-deployment
    spec:
      containers:
        - image: edgehub/deviceshifu-http-http:v0.0.1
          name: deviceshifu-http
          ports:
            - containerPort: 8080
          volumeMounts:
            - name: deviceshifu-config
              mountPath: "/etc/edgedevice/config"
              readOnly: true
          env:
            - name: EDGEDEVICE_NAME
              value: "edgedevice-plc"
            - name: EDGEDEVICE_NAMESPACE
              value: "devices"
        - image: edgehub/plc-device:v0.0.1
          name: plc
          env:
            - name: PLC_ADDRESS
              value: "192.168.0.1"
            - name: PLC_RACK
              value: "0"        
            - name: PLC_SLOT
              value: "1"
            - name: PLC_CONTAINER_PORT
              value: "11111"
      volumes:
        - name: deviceshifu-config
          configMap:
            name: plc-configmap-0.0.1
      serviceAccountName: edgedevice-sa
      

Some general configurations are also required:

Click here to view deviceshifu-plc-configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: plc-configmap-0.0.1
  namespace: deviceshifu
data:
#    device name and image address
  driverProperties: |
    driverSku: PLC
    driverImage: plc-device:v0.0.1
    driverExecution: " "
#    available instructions
  instructions: |
    sendsinglebit:
    sendcontent:
    getcontent:
    getcpuordercode:
#    telemetry retrieval methods
#    in this example, a device_health telemetry is collected by calling hello instruction every 1 second
  telemetries: |
    device_health:
      properties:
        instruction: getcpuordercode
        initialDelayMs: 1000
        intervalMs: 1000

Click here to view deviceshifu-plc-service.yaml

apiVersion: v1
kind: Service
metadata:
  labels:
    app: deviceshifu-plc-deployment
  name: deviceshifu-plc
  namespace: deviceshifu
spec:
  ports:
    - port: 80
      protocol: TCP
      targetPort: 8080
  selector:
    app: deviceshifu-plc-deployment
  type: LoadBalancer

Click here to view edgedevice-plc.yaml

apiVersion: shifu.edgenesis.io/v1alpha1
kind: EdgeDevice
metadata:
  name: edgedevice-plc
  namespace: devices
spec:
  sku: "PLC"
  connection: Ethernet
  address: 0.0.0.0:11111
  protocol: HTTP
status:
  edgedevicephase: "Pending"

Step 3

Add the PLC device to Shifu. Create and start deviceShifu:

kubectl apply -f ../plc_configuration_directory

Operations

Shifu can read and write the memory of the PLC through HTTP requests.

Before the next step, we need to start an nginx container to send and receive HTTP requests, with the following commands:

kubectl run nginx --image=nginx:1.21 -n deviceshifu 
kubectl exec -it nginx -n deviceshifu -- bash

Three instructions are sendsinglebit, getcontent and getcpuordercode. We can execute these instructions on the device via Shifu.

sendsinglebit

sendsinglebit modifies a single bit. It needs the following parameters:

• rootaddress: the name of the memory area. e.g. M for Merker and Q for Digital Output
• address: the address of the memory area
• start: the start position
• digit: the offset from the start position
• value: the new value to set

For example, the command curl "deviceshifu-plc/sendsinglebit?rootaddress=Q&address=0&start=0&digit=1&value=1" will modify the second bit of Q0.1 to 1.

curl "deviceshifu-plc/sendsinglebit?rootaddress=Q&address=0&start=0&digit=1&value=1"; echo

Check the PLC and you will find the second indicator light in Q area is on.

getcontent

getcontent gets the value of a specific address in a memory area. It needs the following parameters:

• rootaddress: the name of the memory area. e.g. M for Merker and Q for Digital Output
• address: the memory area's address
• start: the start position

For example, the command curl "deviceshifu-plc/getcontent?rootaddress=Q&address=0&start=0 will return the value of Q0.0.

curl "deviceshifu-plc/getcontent?rootaddress=Q&address=0&start=0"

getcpuordercode

getcpuordercode gets the static information of PLC.

curl "deviceshifu-plc/getcpuordercode"; echo