Modem Communication ! Urgent

I have to develop an application using MFC & VC++ & Windows APIs  for communicating with the modem .If anybody has an
idea about this , please reply back with a detailed  explanation .
                   Thank you ,
Who is Participating?
piano_boxerConnect With a Mentor Commented:
All commands is sent to the modem using the AT prefix:

1. Initialize moden (
    SEND: ATZ\n    (Or whatever appropriate)
    WAIT: OK, ERROR, (Timeout)

2. Dial phone number
    SEND: ATDT12345678\n (12345678 is the number to call)
    WAIT: CONNECT  (Modem connected OK. Can be followed by connect speed)
          ERROR\r\n    (Error in command)
          NO CARRIER\r\n, NO ANSWER\r\n (No reply from other modem)
          BUSY\r\n     (Line is busy)

2a.  Is CONNECT is the response from dialog then the modem will switch to datamode and you can send/receive data.

3. Disconnect (There are two methods):

    Method 1:   Lower the DTR hardware line
                (EscapeCommFunction(hPort, CLRDTR));

    Method 2:   Send + (plus character) three times with a small
                delay in between. The modem will the switch to
                command mode. Send ATH0\n to hang up.

sankar012898Author Commented:
Edited text of question
sankar012898Author Commented:
Edited text of question
Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

For Win32?
Here is some code for opening any comport and setup parameters.
nPort: 0=COM1, 1=COM2....


HANDLE OpenCommPort(int nPort, int nBaudrateIdx)

    HANDLE hPort;
    CString strPort;
        strPort.Format(_T("COM%d"), nPort);
        strPort.Format(_T("\\\\.\\COM%d"), nPort);

    // Open COM1.....COMx
    hPort = CreateFile(strPort,GENERIC_READ|GENERIC_WRITE,
        0,    /* comm devices must be opened w/exclusive-access */
        NULL, /* no security attrs */
        OPEN_EXISTING, /* comm devices must use OPEN_EXISTING */
        NULL  /* hTemplate must be NULL for comm devices */
        return NULL;

    // Setup timeout values for reading and writing to the port
    ctmo.ReadIntervalTimeout = 100;
    ctmo.ReadTotalTimeoutMultiplier = 1;
    ctmo.ReadTotalTimeoutConstant = 2000;
    ctmo.WriteTotalTimeoutMultiplier = 1;
    ctmo.WriteTotalTimeoutConstant = 1000;
    SetCommTimeouts(hPort, &ctmo);

    const int br[] = { 300, 1200, 2400, 4800, 9600, 14400, 19200 };

    // Setup port to use CTS/RTS hardware flow control with 8 databits
    // 1 stopbit and no parity.

    DCB dcb;
    ZeroMemory(&dcb, sizeof(dcb));
    dcb.DCBlength = sizeof(DCB);
    dcb.BaudRate = br[nBaudrateIdx];
    dcb.fBinary = TRUE;
    dcb.fParity = 0;
    dcb.fOutxCtsFlow = 1;
    dcb.ByteSize = 8;
    dcb.Parity = NOPARITY;
    dcb.StopBits = 0;
    dcb.fDtrControl = DTR_CONTROL_ENABLE;
    dcb.fRtsControl = RTS_CONTROL_ENABLE;
    dcb.fAbortOnError = FALSE;
    if(!SetCommState(hPort, &dcb))
        return NULL;

    return hPort;


To read and write to the port, just use the normal ReadFile()/WriteFile() functions

Here is an example of how to reset the modem:

BOOL ResetModem(HANDLE hPort)
    CString sCmd = _T("Z\n");

    DWORD dwIOLen;
    if(WriteFile(hPort, sCmd, sCmd.GetLength(), &dwIoSize, NULL))
        return TRUE;

    return FALSE;

Off-cause you would want to check the responses from the modem when sending
commands or dialing but that is just basic Win32 IO.
Please refer to online manual about the following functions.

There is an example on the VC5 CD: \Devstudio\Vc\Samples\Sdk\Win32\Comm
Theses sites can also give you some help. 
sankar012898Author Commented:
hi piano_boxer & trestan,
              Thanks for your reply . I understood your  code .
 Infact I have  programmed the COM port myself in a similar way  for communicating  with Barcode readers and printers but I  wanted  to  know  how to  dial a  telephone number by a
program  when the modem is connected to a com port and
 also how to send  data over telephone wires .
sankar012898Author Commented:
Hi piano_boxer,
         Thanks  for your  answer .
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.