The comm/datamodem device class consists of modem devices. You access these devices by using the Win32 file and communications functions. Devices in this class are associated with line devices that support the LINEMEDIAMODE_DATAMODEM media mode, which is specified in the dwMediaModes member of the LINEDEVCAPS structure for the line device.

The lineGetID and phoneGetID functions fill a VARSTRING structure, setting dwStringFormat to the STRINGFORMAT_BINARY value and appending these additional members:

HANDLE hComm; // handle of open comm. device

CHAR szDeviceName[1]; // name of comm. device

The hComm member is the handle of the open communications port. This member is NULL if the port is not yet open or if the dwSelect parameter of lineGetID is not the LINECALLSELECT_CALL value. If a call is active, the service provider typically opens the port itself to get direct control of the communications hardware, but is only required to return a valid handle if the line is connected. The service provider opens the port using the FILE_FLAG_OVERLAPPED value and then configures the port using the settings specified by the lineSetDevConfig function. You can set additional configuration options for the device by using Win32 functions with the returned handle.

The szDeviceName member is a null-terminated ASCII string that specifies the name of the communications port associated with the line, address, or call.

If hComm is a valid handle, you can use it in subsequent calls to Win32 file functions, such as ReadFile and WriteFile, to send and receive data on the call. When you are finished using the communications port and preferably before you use the lineDeallocateCall function to deallocate the call, you must close the port by using the CloseHandle function.

When using the lineGetDevConfig and lineSetDevConfig functions, some service providers require that the configuration data for this device class have the following format:

typedef struct tagDEVCFG {


COMMCONFIG commconfig;


// Device setting information

typedef struct tagDEVCFGDR {

DWORD dwSize;

DWORD dwVersion;

WORD fwOptions;

WORD wWaitBong;


The following is device configuration information for use with the lineGetDevConfig and lineSetDevConfig functions.


Sum of the size of the DEVCFGHDR structure and the actual size of COMMCONFIG structure.


Version number of the Unimodem DevConfig structure. This member can be MDMCFG_VERSION (0x00010003).


Option flags that appear on the Unimodem Option page. This member can be a combination of these values:


Displays the pre-terminal screen.


Displays the post-terminal screen.


Dials the phone manually, if capable of doing so.


Displays the modem tray icon.

Only the LAUNCH_LIGHTS value is set by default


Number of seconds (in two seconds granularity) to replace the wait for credit tone ($).


COMMCONFIG structure that can be used with the Win32 communications and MCX functions.

Software for developers
Delphi Components
.Net Components
Software for Android Developers
More information resources
Unix Manual Pages
Delphi Examples
Databases for Amazon shops developers
Amazon Categories Database
Browse Nodes Database