IOCTL_SERIAL_LSRMST_INSERT

The IOCTL_SERIAL_LSRMST_INSERT DeviceIoControl operation enables or disables the placement of line status and modem status values into the regular data stream that an application acquires through the ReadFile function.

When this line-status and modem-status data placement mode is enabled, status values are preceded in the data stream by an escape character. The user-definable escape character is set by the IOCTL_SERIAL_LSRMST_INSERT operation. Status values consist of 1 to 3 BYTEs. See the Remarks section below for status value details. 

BOOL DeviceIoControl(
  (HANDLE) hDevice,        // handle to device of interest
  IOCTL_SERIAL_LSRMST_INSERT,  // dwIoControlCode, control code of
                           // operation to perform
  (LPVOID) lpInBuffer,     // address of input buffer 
  (DWORD) nInBufferSize,   // size, in bytes, of input buffer 
  NULL,                    // lpOutBuffer is not used; must be NULL
  0,                       // nOutBufferSize is not used;
                           // must be zero
  (LPDWORD) lpBytesReturned,   // pointer to variable to receive
                           // output byte count
  (LPOVERLAPPED) lpOverlapped  // pointer to OVERLAPPED structure
                           // for asynchronous operation
);

Parameters

hDevice
Handle to the object on which the operation is to be performed. To obtain a device handle, call the CreateFile function.
dwIoControlCode
Control code for the operation. This value identifies the specific operation to be performed and the type of device on which the operation is to be performed. Use IOCTL_SERIAL_LSRMST_INSERT for this operation.
lpInBuffer
Pointer to a buffer that contains a single BYTE.

If the BYTE is a nonzero value, it is the desired line-status and modem-status value escape character. The operation will turn the LSRMST_INSERT line-status and modem-status data placement mode on.

If the BYTE is zero, the operation will turn the LSRMST_INSERT line-status and modem-status data placement mode off.

The escape character can not be the XON or XOFF character.

nInBufferSize
Size, in bytes, of the buffer pointed to by lpInBuffer. For this operation, this value should be 1.
lpOutBuffer
Pointer to an output buffer. Not used with this operation. Set to NULL.
nOutBufferSize
Size, in bytes, of the buffer pointed to by lpOutBuffer. Not used with this operation. Set to zero.
lpBytesReturned
Pointer to a DWORD variable.

If lpOverlapped is NULL (nonoverlapped I/O), lpBytesReturned is used internally and cannot be NULL.

If lpOverlapped is not NULL (overlapped I/O), lpBytesReturned can be NULL.

lpOverlapped
Pointer to an OVERLAPPED structure.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, this parameter must point to a valid OVERLAPPED structure. In this case, DeviceIoControl is performed as an overlapped (asynchronous) operation. If the device was opened with the FILE_FLAG_OVERLAPPED flag and lpOverlapped is NULL, the function fails in unpredictable ways.

If hDevice was opened without specifying the FILE_FLAG_OVERLAPPED flag, this parameter is ignored and the DeviceIoControl function does not return until the operation has been completed, or until an error occurs.

Return Values

If the operation succeeds, DeviceIoControl returns a nonzero value.

If the operation fails, DeviceIoControl returns zero. To get extended error information, call GetLastError.

Remarks

Note that an application that uses this scheme must examine each character in the data stream to determine the presence of modem-status or line-status data.

The following values follow the designated escape character in the data stream if the LSRMST_INSERT mode has been turned on :

Value Meaning
SERIAL_LSRMST_ESCAPE Indicates the reception of the escape character itself into the data stream.
SERIAL_LSRMST_LSR_DATA Indicates that a line status change occurred, and data was available in the receive hardware buffer. Following this BYTE is a BYTE value of the line status register is the BYTE present in the receive hardware buffer when the line status change was processed.
SERIAL_LSRMST_LSR_NODATA Indicates that a line status change occurred, but no data was available in the receive hardware buffer.
SERIAL_LSRMST_MST Indicates that a modem status change occurred. Following this BYTE is a BYTE that is the value of the modem status register when the modem status change was processed.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Unsupported.
  Windows CE: Unsupported.
  Header: Declared in winioctl.h.

See Also

Device Input and Output Overview, Device Input and Output Operations, DeviceIoControl, ReadFile