IOCTL_SERIAL_LSRMST_INSERT IOCTL (winioctl.h)

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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 control code. See the Remarks section for status value details.

To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL DeviceIoControl(
  (HANDLE) hDevice,             // handle to device
  IOCTL_SERIAL_LSRMST_INSERT,   // dwIoControlCode
  (LPVOID) lpInBuffer,          // input buffer 
  (DWORD) nInBufferSize,        // size of input buffer 
  NULL,                         // lpOutBuffer
  0,                            // nOutBufferSize
  (LPDWORD) lpBytesReturned,    // number of bytes returned
  (LPOVERLAPPED) lpOverlapped   // OVERLAPPED structure
);

Remarks

Note

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.

Requirements

Requirement Value
Minimum supported client Windows XP
Minimum supported server Windows Server 2003
Header winioctl.h (include Windows.h)

See also