Basic Modbus Example

Baisc Modbus example. Example demonstrates basic usage of QML components provided by CuteHMI.Modbus.3 extension.

To run the example use cutehmi.view.4 tool.

cutehmi.view.4 CuteHMI.Examples.Modbus.Basic.0

Let's make a quick tour over View.qml file.

First thing to notice are CuteHMI imports.

import CuteHMI.Modbus 3.0
import CuteHMI.Services 2.0

Example uses CuteHMI.Modbus.3 and CuteHMI.Services.2 extensions.

Next thing to notice is a configuration of a Modbus server. The server is given an IP address, a port and a slave address.

        TCPServer {
            id: server
 
            host: "127.0.0.1"
            port: 50002
            slaveAddress: 1
        }

Similarly we configure Modbus client.

        TCPClient {
            id: client
 
            host: "127.0.0.1"
            port: 50002
            slaveAddress: 1
        }

We want our server to be managed by CuteHMI.Services.ServiceManager, so that we don't need to worry about its connection status. This is simply done by embedding it inside CuteHMI.Services.Service component.

    Service {
        id: serverService
 
        name: "TCP Server"
 
        TCPServer {
            id: server
 
            host: "127.0.0.1"
            port: 50002
            slaveAddress: 1
        }
    }

Similarly we want the client to be turned into a service. Outside a service client would not perform polling, handle connection errors and so on.

    Service {
        id: clientService
 
        name: "TCP Client"
 
        TCPClient {
            id: client
 
            host: "127.0.0.1"
            port: 50002
            slaveAddress: 1
        }
    }

As the client and the server are configured we can move on to establishing some interaction between them. Let's create a button that will tell the client to send a request to turn on a coil.

            Button {
                text: "Client set coil"
                onClicked: client.requestWriteCoil(10, true)
            }

Once the button is clicked it will send a request to write coil value at address 10. This may look suspicious on a localhost, but the whole communication is done over TCP/IP protocol. Now let's reset coil value to off on the server side.

            Button {
                text: "Server reset coil"
                onClicked: server.requestWriteCoil(10, false)
            }

Now let's introduce CuteHMI.Modbus.CoilController. Controllers typically are a better mean of control as they allow for property binding.

                CoilController {
                    id: coilController
 
                    device: client
                    address: 10
                    onValueChanged: coilSwitch.checked = value
                }

We assign a device using id of of the client. We also set up the same address as used by buttons. We use onValueChanged signal handler to update value of a corresponding switch once the value in the controller changes. The switch itself updates the value of a controller once the user changes its value.

                onCheckedChanged: coilController.value = checked

Value of the coil can be binded to other properties as it is done with active property of status indicator.

                active: coilController.value

The same procedure is repeated for a holding register, of course using different set of controls - adequate to holding register 16 bit integer capacity.

            Button {
                text: "Client set holding register"
                onClicked: client.requestWriteHoldingRegister(10, 2020)
            }
 
            Button {
                text: "Server reset holding register"
                onClicked: server.requestWriteHoldingRegister(10, 0)
            }
 
            SpinBox {
                id: holdingRegisterSpinBox
 
                from: 0
                to: 10000
                value: holdingRegisterController.value
 
                onValueChanged: holdingRegisterController.value = value
 
                HoldingRegisterController {
                    id: holdingRegisterController
 
                    device: client
                    address: 10
                    onValueChanged: holdingRegisterSpinBox.value = value
                }
            }
 
            Label {
                text: holdingRegisterController.value
            }

Last, but not least. We start the services by calling CuteHMI.Services.ServiceManager.start() slot.

    Component.onCompleted: ServiceManager.start()