string[] portList = System.IO.Ports.SerialPort.GetPortNames();
for (int i = 0; i < portList.Length; i++)
{
    string name = portList[i];
    comboBox.Items.Add(name);
}

SerialPort mySerialPort = new SerialPort("COM2");//端口
mySerialPort.BaudRate = 9600;//波特率
mySerialPort.Parity = Parity.None;//校驗位
mySerialPort.StopBits = StopBits.One;//停止位
mySerialPort.DataBits = 8;//數據位
mySerialPort.Handshake = Handshake.Non;
mySerialPort.ReadTimeout = 1500;
mySerialPort.DtrEnable = true;//啟用數據終端就緒信息
mySerialPort.Encoding = Encoding.UTF8;
mySerialPort.ReceivedBytesThreshold = 1;//DataReceived觸發前內部輸入緩沖器的字節數
mySerialPort.DataReceived += new SerialDataReceivedEvenHandler(DataReceive_Method);

mySerialPort.Open();

// Write a string
port.Write("Hello World");

// Write a set of bytes
port.Write(new byte[] { 0x0A, 0xE2, 0xFF }, 0, 3);

// Close the port
port.Close();

string serialReadString;
private void port_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
    serialReadString = port.ReadExisting());
    this.txt1.Invoke( new MethodInvoker(delegate { this.txt1.AppendText(serialReadString); }));
}

void com_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
    // Use either the binary OR the string technique (but not both)
    // Buffer and process binary data
    while (com.BytesToRead > 0)
        bBuffer.Add((byte)com.ReadByte());
    ProcessBuffer(bBuffer);

    // Buffer string data
    sBuffer += com.ReadExisting();
    ProcessBuffer(sBuffer);
}

private void ProcessBuffer(string sBuffer)
{
    // Look in the string for useful information
    // then remove the useful data from the buffer
}

private void ProcessBuffer(List<byte> bBuffer)
{
    // Look in the byte array for useful information
    // then remove the useful data from the buffer
}