C# Serial Port Communication

I am trying to return a value from an RTU by using a serial port connection.  My settings are 19.2k, parity none, 8 and 1.  I am trying retrieve information by typing in a TLP.  The code below is what I currently have from going off another example but I'm not sure how to type in a TLP, click a button to send the data and then receive it back in another text box.

public partial class Form1 : Form
    {
        string myString;

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (serialPort1.IsOpen)
            {
                serialPort1.Close();
            }
            serialPort1.PortName = "COM1";
            serialPort1.BaudRate = 19200;

            serialPort1.Open();
            serialPort1.DtrEnable = true;
            serialPort1.RtsEnable = true;
            if (serialPort1.IsOpen)
            {
                button1.Enabled = true;
                textBox2.ReadOnly = true;
            }
        }

        private void Form1_FormClosing(object sender, FormClosedEventArgs e)
        {
            if (serialPort1.IsOpen)
            {
                serialPort1.Close();
            }
        }

        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (!serialPort1.IsOpen)
            {
                return;
            }
            char[] buff = new char[1];
            buff[0] = e.KeyChar;
            serialPort1.Write(buff, 0, 1);
            e.Handled = true;
        }

        private void DisplayText(object sender, EventArgs e)
        {
            textBox1.AppendText(myString);
        }

        private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {
            myString = serialPort1.ReadExisting();
            this.Invoke(new EventHandler(DisplayText));
        }
    }