我写了一个串口程序！是和一台仪器进行通信，在通讯过程中，我发送一条指令后，仪器会回复一条指令，我要判断回复的指令是否正确，我把接受的数据放在ReceiveData中，每次判断前我要知道接收到的仪器的指令是否更新过，我现在不知道怎么判断接受的的数据是否更新？？
   private void serialPort1_DataReceived(object sender, e)//串口接收数据
        {
           while (serialPort1.BytesToRead > 0)
            {
                    ReceiveData += serialPort1.ReadExisting();//接受的数据放在ReceiveData
            }
            ReceiveData = "";
        }
        private void collect_data_Click(object sender, EventArgs e)//通信过程
        {
            int i;
            sendmesg[1] = "WAV" + wave_set.Text.ToString() + '\r';//x射线波长
            sendmesg[9] = "SKM" + voltage_set.Text+ current_set.Text + '\r';//管电压，管电流
            sendmesg[10] = "SHO" + '\r';//开光栅
            sendmesg[11] = "Q/" + '\r';
                WriteData("SHR"+'\r');
            while (!string.Equals(ReceiveData,'\n' + "C=?" + '\r')) ;
                WriteData("/S" + '\r');
            for (i = 1; i < 13; i++)//这个地方出现问题，因为不知道怎么判断接收的的数据已经更新？？？？？？？？？？
            {
                while (!string.Equals(ReceiveData,'\n' + "C=?" + '\r')) ;
                WriteData(sendmesg[i]);
            }
            button3.Enabled = true;
        }

顶下