[UWP] serialdevice.cleartosendstate always returns false

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C#

serial-port

Win10

I use two FT232RL (FTDI) USB to Serial adapters to utilize UART communication with RTS/CTS flow control between 2 PCs. My hardware configuration: TX<-->RX; RX<-->TX; CTS<-->RTS; RTS<-->CTS; GND<-->GND.

I enable RTS signal of one adapter and want to get the CTS state of the other adapter. I used SerialDevice.PinChanged event to catch this change. My app in computer B calls PinChanged handler whenever I enable/disable RTS signal of computer A and I could verify that CTS signal of computer B is changed (by checking the value of PinChangedEventArgs.PinChange). However, the value of SerialDevice.ClearToSendState is always false. Therefore, I could not determine whether other device(computer B) is ready to receive data or not.

I used following code to configure serial device and handle event:

private async void ConnectDevice(string entryId)
{
    try
    {
        // serialPort is a private variable of MainPage
        serialPort = await SerialDevice.FromIdAsync(entryId);

        // Configure serial settings
        serialPort.WriteTimeout = TimeSpan.FromMilliseconds(1000);
        serialPort.ReadTimeout = TimeSpan.FromMilliseconds(1000);
        serialPort.BaudRate = 9600;
        serialPort.Parity = SerialParity.None;
        serialPort.StopBits = SerialStopBitCount.One;
        serialPort.DataBits = 8;
        serialPort.Handshake = SerialHandshake.RequestToSend;
        serialPort.PinChanged += SerialPort_PinChanged;

        // Listien to incomming data
        Listen();
    }
    catch (Exception ex)
    {
        status.Text = ex.Message;
    }
}

private async void SerialPort_PinChanged(SerialDevice sender, PinChangedEventArgs args)
{
    switch (args.PinChange)
    {
        case SerialPinChange.ClearToSend:
            // If device is ready, write data
            if (serialPort.ClearToSendState)
                await WriteAsync();
            break;
        default:
            break;
    }
}

Is my implementation correct? How could I use RTS/CTS flow control in a UWP app?

What I have tried:

I tried to set SerialDevice.Handshake as SerialHandshake.None and use another type of adapter. But it still does not work.