问读取串口C#.net 2.0以获取称重机输出时出现问题

EN

public string readWeight()
{
    string lastError = "";
    string weightData = "";
    SerialPort port = new SerialPort();
    port.PortName = "COM1";
    port.BaudRate = 9600;
    port.Parity = Parity.Even;
    port.DataBits = 7;
    port.StopBits = StopBits.One;
    port.Handshake = Handshake.RequestToSend;
    try {
        port.Open();
        weightData = port.ReadExisting();
        if(weightData == null || weightData.Length == 0) {
            lastError = "Unable to read weight. The data returned form weighing machine is empty or null.";
            return lastError;
        }
    }
    catch(TimeoutException) {
        lastError = "Operation timed out while reading weight";
        return lastError;
    }
    catch(Exception ex) {
        lastError = "The following exception occurred while reading data." + Environment.NewLine + ex.Message;
        return lastError;
    }
    finally {
        if(port.IsOpen == true) {
            port.Close();
            port.Dispose();
        }
    }
    return weightData;
}