C# SerialPort的Datareceive事件触发后，BytesToRead的值有时候为零

下位机每隔0.5秒通过串口传25个字节到上位机，串口接收到数据后处理并用zedgraph控件绘制实时曲线图，程序运行几分钟后，Datareceive事件触发后，BytesToRead的值有时候为0，有时是25，也有时是50，界面刷新有时也不是0.5秒。
接收程序：

        private void serialPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            try
            {
                if (mySerialPort.IsOpen)
                {
                    Thread.Sleep(10);
                    int count = mySerialPort.BytesToRead;
                        byte[] data = new byte[count];
                        mySerialPort.Read(data, 0, count);
                        if (data[0] == 0x01 && data[1] == 0x03)
                        {
                            this.Invoke(textChanged, data, count);
                        }
                }
            }
            catch (Exception err)
            {
                throw err;
            }
        }

处理程序：

        textChanged += new UpdateTextEventHandler(ChangeText); 
        private delegate void UpdateTextEventHandler(byte[] buffer,int m);//定义委托
        private event UpdateTextEventHandler textChanged;//定义事件 
        private void ChangeText(byte[] buffer,int m) //事件处理方法
        {
            s1 = "";
            Array.Copy(buffer, 3, float_byte1, 0, 4);
            Array.Copy(buffer, 8, float_byte2, 0, 4);
            Array.Copy(buffer, 13, float_byte3, 0, 4);
            Array.Copy(buffer, 18, float_byte4, 0, 4);
            temperture[0] = BitConverter.ToSingle(float_byte1, 0);
            temperture[1] = BitConverter.ToSingle(float_byte2, 0);
            temperture[2] = BitConverter.ToSingle(float_byte3, 0);
            temperture[3] = BitConverter.ToSingle(float_byte4, 0);
            textBox1.Text = temperture[0].ToString();
            textBox2.Text = temperture[1].ToString();
            textBox3.Text = temperture[2].ToString();
            textBox4.Text = temperture[3].ToString();
            for (int i = 0; i < m; i++)
            {
                s1 += buffer[i].ToString("X2");
                s1 += " ";
            }
            textBox5.Text = s1.ToString();
            if (Curve_Flag == 1)
            {
                i++;
                creatGraph(temperture[j]);
            }


        }

zedgraph绘图：

public void creatGraph(float temp)
        {
            double x = (double)i;
            double y = Convert.ToDouble(temp);
            list.Add(x, y);
            myCurve = zedGraphControl1.GraphPane.AddCurve("", list, Color.Red, SymbolType.None);
            //myCurve.Symbol.Fill = new Fill(Color.Blue);//填充数据点
            zedGraphControl1.AxisChange();//画到zedGraphControl1控件中，此句必加
            zedGraphControl1.Refresh();//重新刷新
        }

串口读取数据的时候不能加Thread.Sleep(10);
你加了延迟表明你想丢弃一些数据，这是不对的。

你每次延时10ms并不能保证数据已完全接收到了，我都是这么读：
byte[] BufRead = new byte[100];
int NowReadint = 0;
int AllReadint = 0;
bool IsSucc = false;
bool IsError = false;
DateTime ReadStartTime = DateTime.Now;
do
{
NowReadint = SPort.BytesToRead;
NowReadint = SPort.Read(BufRead, AllReadint, NowReadint);
AllReadint += NowReadint;
//你的判断条件
if (?????)
{
IsSucc=true;
}
if (DateTime.Now.Subtract(ReadStartTime).TotalMilliseconds > 2000)
{
IsError = true;
break;
}
Thread.Sleep(20);
} while (!IsSucc);

要用一个缓冲来存储串口读来的数据，然后再来判断，这样就不会丢数据