C# .NET How to read continuously an input from a PLC through Modbus

Question

I am using the EasyModbus library from GitHub to communicate to the PLC, I tried the required functions and I accomplish to run them on visual studio 2019 individually, and worked fine.

I did a basic program to switch on and off an output of the PLC by using two buttons. And also reading/monitoring an output from the same PLC by changing two colors(yellow On and red Off) on C# form1.

Then, when I click the on and off buttons they work fine but on the other hand, the reading/monitoring function didn't work. I need someone to illustrate some modifications how to run these functions simultaneously and at the same time changing the on/off status of the output and also reading the status of an output of the PLC.

Thank you

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using EasyModbus;
using System.Windows.Forms;

namespace PLC
{
    public partial class Form1 : Form
    {
        ModbusClient modbusClient;
        
        public Form1()
        {
            InitializeComponent();
            ON.Visible = true; //yellow
            OFF.Visible = true;//red
            modbusClient = new ModbusClient("COM5");//communication settings
            modbusClient.UnitIdentifier = 1;
            modbusClient.Baudrate = 19200;
            modbusClient.Parity = System.IO.Ports.Parity.None;
            modbusClient.StopBits = System.IO.Ports.StopBits.One;
            modbusClient.Connect();


    // reading function begin
            var value = modbusClient.ReadCoils(0, 1);// read coil zero and if it is true change color yellow else change color to red
            

            if (value[0] == true)
            {
                ON.Visible = true;
                OFF.Visible = false;
            }
            else
            {
                ON.Visible = false;
                OFF.Visible = true;
            }

    // end of reading function

        } 
        private void button1_Click(object sender, EventArgs e)// on button
        {
            modbusClient.WriteSingleCoil(0, true);//toggle coil zero to on
        }

        private void button2_Click(object sender, EventArgs e)// off button
        {
            modbusClient.WriteSingleCoil(0, false);// toggle coil zero to off
        }
    }
}

score 0 · Answer 1 · answered Nov 13 '21 at 21:50

Try to use timers. Here is your modified code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using EasyModbus;
using System.Windows.Forms;


namespace StackOverflowAnswer
{
    public partial class Form1 : Form
    {
        ModbusClient modbusClient;

        public Form1()
        {
            InitializeComponent();
            ON.Visible = true; //yellow
            OFF.Visible = true;//red
            // ### changed to TCP - I have no COM ports ###
            modbusClient = new ModbusClient("127.0.0.1", 502); //communication settings
            //modbusClient.UnitIdentifier = 1;
            //modbusClient.Baudrate = 19200;
            //modbusClient.Parity = System.IO.Ports.Parity.None;
            //modbusClient.StopBits = System.IO.Ports.StopBits.One;
            modbusClient.Connect();

            #region Modified section
            var readModBusTimer = new Timer()
            {
                Interval = 500,
                Enabled = true
            };

            readModBusTimer.Tick += ReadModBusTimer_Tick;
            readModBusTimer.Start();

            // reading function begin
            ReadCoils();

            // end of reading function

        }

        private void ReadCoils()
        {
            var value = modbusClient.ReadCoils(0, 1);// read coil zero and if it is true change color yellow else change color to red


            if (value[0] == true)
            {
                ON.Visible = true;
                OFF.Visible = false;
            }
            else
            {
                ON.Visible = false;
                OFF.Visible = true;
            }
        }

        private void ReadModBusTimer_Tick(object sender, EventArgs e)
        {
            ReadCoils();
        }
        #endregion
        private void button1_Click(object sender, EventArgs e)// on button
        {
            modbusClient.WriteSingleCoil(0, true);//toggle coil zero to on
        }

        private void button2_Click(object sender, EventArgs e)// off button
        {

            modbusClient.WriteSingleCoil(0, false);// toggle coil zero to off
        }


    }
}

C# .NET How to read continuously an input from a PLC through Modbus

1 Answers1