请教(Money酬谢)---C#读取电子称串口数据，及时显示在TextBox控件

公司要求将电子称串口数据与电脑串口相连接，实现数据的即时通讯，其主要用来称产品，然后计算出相应个数。以下是我写的代码，基本都是参照网上高人写的。
但是就是不能实现这个自动读取电脑称仪表数据的功能，以下是程序核心代码。
哪位高人能指点一下，本人感激万分。如果有朋友愿意协助下，定以适当Money作为酬谢。QQ:526284639
 private void Form2_Load(object sender, EventArgs e)
        {
            InitPort();
        }
        private void InitPort()
        {      
            com.BaudRate = 9600;
            com.PortName = "COM4";
            com.DataBits = 8;
            com.Parity = Parity.None;
            com.StopBits = StopBits.One;
            com.WriteTimeout = 3000;
            com.ReadTimeout = 3000;
            com.ReceivedBytesThreshold = 1;
            com.DtrEnable = true;
            com.RtsEnable = true;      
            com.DataReceived += new SerialDataReceivedEventHandler(com_DataReceived);
            if (!com.IsOpen)
            {
                com.Open();
            }
            else
            {
                MessageBox.Show("Please open relative port");
                return;
            }
        }

        private void com_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {

            try
            {
                   if (!com.IsOpen)
            {
                com.Open();
            }
            com.ReadTimeout = 500;
            Thread.Sleep(500);
            string res = "";
            byte[] buffer = new byte[com.BytesToRead];
           // MessageBox.Show(buffer.Length.ToString());
            com.Read(buffer, 0, buffer.Length);
            res = System.Text.Encoding.ASCII.GetString(buffer);
            if (res == "")
            {
                MessageBox.Show("串口读取数据为空，参数设置是否正确!");           
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }            
        }
   private void sendDataRequest()
        {
            byte[] arrByte = new byte[2];
            //发送命令 1BH+70H  与电子称通讯，读取电子称数据，16进制  
            arrByte[0] = Convert.ToByte(0x1B);
            arrByte[1] = 0x70;
            com.Write(arrByte, 0, 2);
            byte[] buffer = new byte[com.BytesToRead];         
        }