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.
dwIoControlCode = IOCTL_SERIAL_LSRMST_INSERT; // operation code
lpInBuffer; // address of input buffer
nInBufferSize; // size of input buffer
lpOutBuffer = NULL; // address of output buffer; not used; must be NULL
nOutBufferSize = 0; // size of output buffer; not used; must be zero
lpBytesReturned; // address of actual bytes of output
Parameters
lpInBuffer
Points 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
Specifies the size, in bytes, of the buffer pointed to by lpInBuffer. For this operation, this value should be 1.
lpOutBuffer
Points to an output buffer. Not used with this operation. Set to NULL.
nOutBufferSize
Specifies the size, in bytes, of the buffer pointed to by lpOutBuffer. Not used with this operation. Set to zero.
lpBytesReturned
Points to a DWORD that receives the actual size, in bytes, of the data stored into lpOutBuffer.
Return Values
If the operation succeeds, DeviceIoControl returns TRUE.
If the operation fails, DeviceIoControl returns FALSE. 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. |
See Also