Check balance using USSD Command in C#

Question

I update for this question and know it worked correctly..

I try to check balance in my mavecom modem but I got no response in my textbox. It stays empty.

Here my code :

private SerialPort _port;

private void simpleButton1_Click(object sender, EventArgs e)
    {
        _port = new SerialPort();
        _port.PortName = cbPort.Text;
        _port.BaudRate = 115200;
        _port.Parity = Parity.None;
        _port.DataBits = 8;
        _port.StopBits = StopBits.One;
        _port.Handshake = Handshake.RequestToSend;

        port.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived);
        port.Open();

        port.Write("AT+CUSD=1,\"" + txtUSSD.Text + "\",15" + "\r");
    }

private void port_DataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        try
        {
            // read the response.
            var response = ((SerialPort)sender).ReadLine();

            // Need to update the txtProvider on the UI thread .
            //showing result in txtOutput based on txtProvider USSD Command
            this.Invoke(new Action(() => txtOutput.Text = response)); 
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

This is solved and can be use to check the balance....

Also good idea to register to `DataReceived` before opening the serial port. — Niels Filter, Jul 28 '15 at 13:13
Don't add the words "[Solved]" to the title, that is not how it works. Tick the correct answer instead. — JK., Nov 16 '15 at 03:10
no correct answer for this question,.. i just fix it myself and wanna the other reader can know and use this sample code,.. thanks — aminvincent, Nov 16 '15 at 03:17

score 1 · Accepted Answer · edited May 23 '17 at 12:04

Good start, you are properly terminating AT command lines with \r (not using WriteLine or any other such incorrect approaches that unfortunately are common beginner problems). However the format of the command is defined in 27.007 to be

AT+CUSD=[<n>[,<str>[,<dcs>]]]
...
Defined values
...
<str>: string type USSD-string ...

and string parameters shall always be enclosed with double quotes (V.250 chapter 5.4.2.2 String constants: String constants shall be bounded at the beginning and end by the double-quote character).

So without knowing the textProvider object in detail I am quite confident that your code should be

port.Write("AT+CUSD=1,\"" + txtProvider.Text + "\",15" + "\r");

but note that if txtProvider.Text contains any " characters they must be escaped (not as \" by the way, check 5.4.2.2).

However even with the above fixed you need to seriously rework your reception handling. You MUST read and parse every single line of response from the modem until you get a Final result code back (most commonly OK or ERROR, but there are several others). Any other way cannot work reliably. See this answer for pseudo code structure of how to do it properly.

And as commented, you are closing the port too early.

@hlovdal when i change ussd at command like `port.Write("AT+CUSD=1,\"" + txtProvider.Text + "\",15" + "\r");` nothing happen,...no result in txtOutput — aminvincent, Jul 29 '15 at 04:05

Check balance using USSD Command in C#

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