I can't receive data from CardReader with SerialPort class

Question

I am able to receive data using serial port debug tools with the Modbus protocol.

The parameters below are the same. However, I set a breakpoint in the DataReceived method but it is never encountered. Below is my program:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO.Ports;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace TestBalance
{
    public partial class Form1 : Form
    {
        SerialPort sp;
        public Form1()
        {
            InitializeComponent();
            sp = new SerialPort("COM21", 9600, Parity.None, 8, StopBits.One);
            sp.Open();
            sp.ReceivedBytesThreshold = 1;
            sp.RtsEnable = true;
            sp.DtrEnable = true;
            sp.DataReceived+=sp_DataReceived;
            sp.Write("01 03 100b 0002 b109");
            Thread.Sleep(200);
            //string message= sp.ReadExisting();
            //MessageBox.Show(message);
        }

        private void sp_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            string message = sp.ReadLine();
            MessageBox.Show(message);
        }
    }
}

Answer 1

Okay, without having much information about how your device works. I can only take some guesses at what may be your problem.

In the case that your device is synchronous, make sure that you are sending an end-of-line (EOL) sequence to the device. Some devices will need an EOL in order to signal the sending of data. This EOL is often carriage-return followed by line-feed, or just carriage-return. So you may have to change your data to "01 03 100b 0002 b109\\r" . Notice that I have added a carriage-return. Also, you can use "\\n" for line-feed or "\\r\\n" for both carriage-return and line-feed.

Also, not knowing what kind of a device you are using. You would do well to make sure that you have the serial-port settings all correct. Make sure that the baud-rate is actually supposed to be 9600. You can't just choose whatever you want, the device you are talking to will have a preset baud-rate inside the hardware that you are required to use.

Additionally, make sure you have the COM port number correct. Open up device-manager and make sure you are talking to the correct port.

Finally, I have never seen anyone subscribe to the SerialPort class how you did it. Change your code to properly match the MSDN example right here . Use:

this.sp.DataReceived 
    += new SerialDataReceivedEventHandler(this.sp_DataReceived);