COM Exception on serial port RRS feed

  • Question

  • Hi! 

    I'm working on reading a serial port where is attached a USB/Modbus converter. I wrote the code following the official Microsoft UART example ( write and read  from a serial port).

    But it randomly gives me this type of exception.(first code block)

    Checking on serial port I figured out that the message sent like"hello" sometimes is sent two times consequently like "hellohello" which makes out the issue.

    How can I avoid it? May I need a cancellation token? Can someone give me some advice on this topic? thank you very much!

    "System.Runtime.InteropServices.COMException HResult=0x800710DD Messaggio=L'identificatore di operazione non è valido. L'identificatore di operazione non è valido. Origine=Windows Analisi dello stack: at Windows.Storage.Streams.DataReader.LoadAsync(UInt32 count) at DQ61_Quanta.ModBus.<ReadAsync>d__9.MoveNext() in C:\Users\mtroplini\source\repos\DQ61_Alfa\DQ61_Quanta\ModBus.cs:line 88 at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at DQ61_Quanta.MainPage.<VisualizzaDati>d__13.MoveNext() in C:\Users\mtroplini\source\repos\DQ61_Alfa\DQ61_Quanta\MainPage.xaml.

    using System;
    using System.Diagnostics;
    using Windows.UI.Xaml;
    using Windows.UI.Xaml.Controls;
    using Windows.UI.Xaml.Media;
    using System.Threading.Tasks;
    using Windows.UI;
    namespace DQ61_Quanta
        public sealed partial class MainPage : Page
        {//non relevant code           
            private DispatcherTimer Timer;
            private string Ricevuto;
            //non relevantcode
            public MainPage()
            private async void MainTimer(object sender, object e)
                    if (modBus.Opened)
                        await modBus.WriteAsync();
                catch (Exception ex)
                    Debug.WriteLine("Errore riscontrato al Timer:" + ex);
            } //Timer Tick a 10 sec
            private void AvvioTimer()
                Timer = new DispatcherTimer();
                Timer.Interval = TimeSpan.FromSeconds(10);
                Timer.Tick += MainTimer;
            } //avvio timer set a 10 sec
            public async void VisualizzaDati()
                if (modBus.Opened)
                    Ricevuto = await modBus.ReadAsync(1024);
                    if (Ricevuto != null)
                        probDATA = F03.TryParse(Ricevuto);
                    if (iotHUB.Opened_)
            } //funzione per visualizzare i dati, farci un parse, e inviarli ad iot hub

            public async Task WriteAsync()
                DataWriter dataWriter = new DataWriter(PortaSeriale.OutputStream);
                #region: conversione in hex
                string Funzione03 = "0x01 0x03 0x80 0x01 0x00 0x04 0x3C 0x09";
                // Spezzo Array negli spazzi //converto in byte base 16// Passo ad array
                byte[] bytes = Funzione03.Split(' ').Select(item => Convert.ToByte(item, 16)).ToArray(); 
                // Converto in Hexadecimal, formato invio "01-03-80-... ecc"
               // string HexMessage = string.Join("-", bytes.Select(item => item.ToString("X2"))); ma serve? XD
                // standard per scrittura dati al seriale collegando e scollegando il buffer
                await dataWriter.StoreAsync();
                dataWriter = null;
            } //scrittura asincrona sul buffer della porta COM
            public async Task<string> ReadAsync(uint ReadBufferLength)
                Task<UInt32> loadAsyncTask;
                byte[] ByteLettura = null;
                // Set InputStreamOptions per completare la lettura asincrona di 1 o + byte
                dataReader.InputStreamOptions = InputStreamOptions.Partial;
                // creazione task per aspettare dati alla serialPort.InputStream
                loadAsyncTask = dataReader.LoadAsync(ReadBufferLength).AsTask();
                UInt32 bytesRead = await loadAsyncTask; //base 32bit
                if (bytesRead > 0) //se leggi byte, convertili in Hexadecimal
                    #region: conversione in hex
                    ByteLettura = dataReader.ReadBuffer(bytesRead).ToArray();
                    string HexMessage = string.Join("-", ByteLettura.Select(item => item.ToString("X2")));
                    return HexMessage;
                return $""; //ritorna nulla se i byte letti sono vuoti

    **cleared from non relevant code*

    • Edited by LemonPies Tuesday, November 20, 2018 3:04 PM
    Monday, November 12, 2018 8:18 AM

All replies

  • Hi LemonPies,

    Thank you for posting here.

    For your question, what is the type of your project?

    According to your error message, we could not make sure what cause the error. I try to test your. How do you send the message?

    Please provide more details.

    Best Regards,


    MSDN Community Support
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    Wednesday, November 14, 2018 7:35 AM
  • Hi Wendy, sorry for my late reply.

    So my project can be described as: getting data from a device throught a modbus rsu 485 (the device is connected to a raspberry pi with a modbus/usb converter). 

    The message (wich is the modbus query to read registers) is sent from the serial port of RPI using DataReader like:

                await dataWriter.StoreAsync();
                dataWriter = null;

    (I have modified the post in order to obscure my azure personal key)

    Monday, November 19, 2018 8:05 AM
  • nothing found? :(
    Friday, November 23, 2018 3:55 PM