How do I read continuous values displaying on a device(motioncontroller) in GUI using C#

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C#

How do i read continuous values which are displayed on a device(ESP 301 Motion Controller) in GUI using C# (WFA).

I have a RS232 cable connected.

Correct me if i am wrong .Is't like i add the device's .dll(File) as reference to the file and then use the Data sheet's ASCII commands to read (display) which is on Device's Panel..?

What I have tried:

using System;
using System.Drawing;
using System.Windows.Forms;
using System.IO.Ports;


namespace MotionController
{
    public partial class Form1 : Form
    {

        public Form1()
        {
            InitializeComponent();
            getavailableports();
        }
        void getavailableports()
        {
            String[] ports = SerialPort.GetPortNames();
            comboBox1.Items.AddRange(ports);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (comboBox1.Text == "") 
               {
                MessageBox.Show("Select the COM Port", "Error" ,
                                 MessageBoxButtons.OKCancel,
                                 MessageBoxIcon.Error);
               }
            else
            {
                SerialPort SerialPort1 = new SerialPort("COM1", 9600);
                SerialPort1.Open();
                button1.BackColor = Color.Green;
                button2.BackColor = Color.Transparent;
                if (SerialPort1.IsOpen)//if the serialport is open
                {
                    button1.Enabled = false;//disable the start button
                    button2.Enabled = true;//enable the stop button
                                      
                }
            }
        }
            

        private void button2_Click(object sender, EventArgs e)
        {
            SerialPort SerialPort1 = new SerialPort("COM1", 9600);
            SerialPort1.Close();
            button2.BackColor = Color.Red;
            button1.BackColor = Color.Transparent;
            button1.Enabled = false;//disable the start button
            button2.Enabled = true;//enable the stop button
       }
  

// Uncomplete Code - Displaying Values..?

        private void textBox1_TextChanged(object sender, EventArgs e)
        {
            SerialPort SerialPort1 = new SerialPort("COM1", 9600);
            SerialPort1.Open();
            if (SerialPort1.IsOpen == true)
            {
                int OpenInstrument(string strCOM1,int 9600);
                string strCOMPort: SerialPort.Port(); 
                int baudrate: 9600;
                SerialPort1.ReadLine(3MD?);
                return;
            }


        }
    }
    }