data event handler to serial port is not triggering?

[ravikiran32]

I am just a beginner and i would like to send sms using 5800 nokia piece. What i would like to do is send "at" command to mobile and read response "OK" from the port(sent by the mobile). I can send commands and get response through hyperterminal but it is not working with my code, i learnt that in my code "SerialDataReceivedEventHandler" is not triggering. Please assit me in developing the code.
here is the code i have written.

SerialPort sp = new SerialPort("com1", 9600, Parity.None, 8, StopBits.One);
    public AutoResetEvent receivenow;
 private void button1_Click(object sender, EventArgs e)
        {
         try
            {
                receivenow = new AutoResetEvent(false);
                sp.ReadTimeout = 300;             //300
                sp.WriteTimeout = 300;           //300
                sp.Encoding = Encoding.GetEncoding("iso-8859-1");
                sp.DataReceived += new SerialDataReceivedEventHandler(sp_datareceived);
                sp.RtsEnable = true;
                sp.DtrEnable = true;
                testSMS();
            }
            catch (Exception ex) { MessageBox.Show(ex.ToString()); }
       
        }
        private void testSMS()
        {
            receivenow = new AutoResetEvent(false);
            sp.Open();
            sp.DiscardInBuffer();
            sp.DiscardOutBuffer();
            receivenow.Reset();
            sp.WriteLine("AT" + "\r");
            
              }

        private void sp_datareceived(object sender, SerialDataReceivedEventArgs args)
        {
            
                 receivenow.Set();
                string responsetocmd = sp.ReadExisting();
                label1.Text = responsetocmd;
              

        }

thanks in advance..........