串口发送数据接收数据问题。

 private void Form1_Load(object sender, EventArgs e)

        {

           if (cbCom.Items.Count > 0)

            {

                cbCom.SelectedIndex = 0;

                sp1.ReceivedBytesThreshold=1;

                sp1.BaudRate = 9600;

                sp1.DtrEnable = true;

                sp1.RtsEnable = true;

                sp1.ReadTimeout = 1000;

                sp1.ReceivedBytesThreshold = 1;

                sp1.DataReceived += new 

                SerialDataReceivedEventHandler(this.Sp1_DataReceived);

                sp1.Open();

            }

        }

        private void Sp1_DataReceived(object sender, SerialDataReceivedEventArgs e)

        {

            if (sp1.IsOpen)     

            {



                DateTime dt = DateTime.Now;

                txtReceived.Text += dt.GetDateTimeFormats('f')[0].ToString() +"\r\n";

                try

                {

                    Byte[] receivedData = new Byte[sp1.BytesToRead];      

                    sp1.Read(receivedData, 0, receivedData.Length);         

                    AddContent(new UTF8Encoding().GetString(receivedData));

                }

                catch (System.Exception ex)

                {

                    MessageBox.Show(ex.Message, "出错提示!!!!!");

                    txtSendStr.Text = "";

                }

            }

            else

            {

                MessageBox.Show("请打开某个串口", "错误提示");

            }

        }