C#串口编程求助

pc与mcu通信，每帧为7byte 帧格式为起始位0x80--上位机地址---下位机地址---传感器编号---命令---数据1----数据0
mcu端处理流程如下：(中断接收)
  (1)接收帧头，如接收正确，状态机跳到(2)，否则状态机停留(1)
  (2)接收上位机地址，其余据上类推....
当一帧数据接收完成后，rx_receive_finished_flag置1  代码如下：

void USART1_IRQHandler(void)
{
if(USART_GetFlagStatus(USART1,USART_FLAG_RXNE)==SET)
{
USART_ClearFlag(USART1,USART_FLAG_RXNE);
rx_temp=USART_ReceiveData(USART1);

switch(rx_state)
{
case FRAME_HEAD_STATE:
if(rx_temp==0x80)
rx_state=UP_ADDR_STATE;
break;
case UP_ADDR_STATE:
if(up_addr==0x00)
{
up_addr=rx_temp;
rx_state=LOW_ADDR_STATE;
}
else if(rx_temp==up_addr)
rx_state=LOW_ADDR_STATE;
else
rx_state=FRAME_HEAD_STATE;
break;
case LOW_ADDR_STATE:
if(rx_temp==low_addr)
rx_state=SENSOR_ADDR_STATE;
else
rx_state=FRAME_HEAD_STATE;
break;
case SENSOR_ADDR_STATE:
curr_sensor_addr=rx_temp;
rx_state=CMD_DATA_STATE;
rx_cnt=2;
break;
case CMD_DATA_STATE:
rx_data[rx_cnt]=rx_temp;
if(rx_cnt>0)
rx_cnt--;
else
{
rx_cnt=0;
rx_receive_finished_flag=1;
rx_state=FRAME_HEAD_STATE;
}
break;
default:
rx_state=FRAME_HEAD_STATE;
break;
}

}
}

由于不熟悉上位机软件，故将上述方法借鉴与C#的串口编程中。（上位机发送一帧数据，下位机收到后即返回收到的那帧数据）
自认为下面上位机接收是基于中断方式，当一帧数据接收完成后 rx_receive_finished_flag = true;
（定时器在发送数据时启动，200ms后检测rx_receive_finished_flag == true？并输出相应消息，用以提示下位机是否
正确收到数据帧）

private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)     -----------##1
        {
            byte rx_temp = 0;
            rx_temp = (byte)serialPort1.ReadByte();
            serialPort1.DiscardInBuffer();

            switch (rx_state)
            {
                case FRAME_HEAD_STATE:
                    if (rx_temp == 0x80)
                        rx_state = UP_ADDR_STATE;
                    break;
                case UP_ADDR_STATE:
                    if (rx_temp == frame[1])
                        rx_state = LOW_ADDR_STATE;
                    else
                        rx_state = FRAME_HEAD_STATE;
                    break;
                case LOW_ADDR_STATE:
                    if (rx_temp == frame[2])
                    {
                        rx_state = CMD_DATA_STATE;
                        rx_data_cnt = 2;
                    }
                    else
                        rx_state = FRAME_HEAD_STATE;
                    break;
                case CMD_DATA_STATE:
                    buffer[rx_data_cnt] = rx_temp;
                    if (rx_data_cnt > 0)
                        rx_data_cnt--;
                    else
                    {
                        rx_data_cnt = 0;
                        rx_receive_finished_flag = true;
                        rx_state = FRAME_HEAD_STATE;
                    }
                    break;
            }

        }

很遗憾，每次发送后定时器弹出的消息都是“ERROR”，而下位机显示屏上显示的数据却是正确的接收数据----显然上位机接收处理部分出了问题，在哪里？
该怎么修正？？

将上位机接收部分改为
//=========================================================================================
        //接收数据
        private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)   ----------##2
        {
            int bytes = serialPort1.BytesToRead;
            byte[] buffer = new byte[bytes];
            serialPort1.Read(buffer, 0, buffer.Length);
            string str = ByteArrayToHexString(buffer).Trim();
            if (textBox2.Text == "")
                textBox2.Text = str;
            else
                textBox2.Text = textBox2.Text + " " + str;
        }
文本显示数据和发送数据是一致的。
糊涂了，不清楚##1为什么不对，serialPort1_DataReceived是每有一byte进入接收缓冲区就触发一次还是....？ --------------------编程问答-------------------- 不太懂 --------------------编程问答-------------------- ding --------------------编程问答-------------------- 简单的讲，就是能不能每接收一个字节就触发一次中断

补充：.NET技术 ,  C#