Receiving data from COM3 port gives error?

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I am trying to read and write data on serial port (COM3) and my write method works well but read method doesn't ,I showed my code below please have a look their and correct me if i am going wrong.

Thanks.

C#

public partial class Form1 : Form
    {
        private SerialPort port = new SerialPort("COM3");

        public Form1()
        {
            InitializeComponent();
        }

        public void port_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            string indata = port.ReadExisting();
            textBox1.Text = indata;
        }

        private void Enable_Click(object sender, EventArgs e)// enable button
        {
            port.BaudRate = 9600;

            port.Open();

            if (port.IsOpen)
                {
                    Enable.Enabled = false;
                    Disable.Enabled = true;
                }
        }

        private void Disable_Click(object sender, EventArgs e) // disable button
        {
            if (port.IsOpen)
            {
                port.Close();
                Enable.Enabled = true;
                Disable.Enabled = false;
            }
        }

        private void button1_Click(object sender, EventArgs e) // send button
        {
            try
            {
                string strToSend;
                strToSend = textBox2.Text;

                if (port.IsOpen)
                {
                    port.Write(strToSend);
                    port.Close();
                }
                else
                {
                    port.Open();
                    port.Write(strToSend);
                    port.Close();
                }
            }
            catch(Exception es) { MessageBox.Show(es.Message); }
        }

        private void button2_Click(object sender, EventArgs e) //receive button
        {
            try
            {
                port.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived);
                port.Open();
                Application.Run();
            }
            catch (Exception es) { MessageBox.Show(es.Message); }
        }
    }

Posted 18-Sep-15 19:54pm

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[no name] 20-Sep-15 9:39am

Have a look here. It is Basic and easy to understand:
Serial Comms in C# for Beginners[^]

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maurizio ferreira · Answer 1 · 2015-09-18T21:03:00

Hello,
I don't have at hands a dev environment to test it,
so I can give you only generic advices.

First of all, why do you write the initialization statements in the button2_click procedure ?

I would move it in the constructor, just after initialize_components.
that is :

C#

public Form1()
{
  InitializeComponent();
  port.BaudRate = 9600;
  port.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived);
}

After that you should remove the Application.run() statement from the button2.click statement.

Application.Run() should be called just after having created the main form,
from the application main procedure so that the application can correctly handle any events that happens to it.

Third, try to understand what the error message say and let us know about it.

Fourth, how can the sender of the data knows it is time to send it ?
There is a kind of 'protocol' between this application and the sender ?

Does the sender reply to a message sent to it by this application or it sends data asynchronously ?

If this is the case, you should leave the port open all the time, that is, open it at program start and close it at program termination.

Best regards.
Maurizio.

Richard MacCutchan · Answer 2 · 2015-09-18T22:04:00

ReadExisting[^] will only read whatever is available at the port at that moment. You only try to read when the button is clicked so there is no synchronisation between your application and the port. You need to look for data continuously when you have received an indication that there is some available.

Receiving data from COM3 port gives error?

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