How to toggle RTS and DTR lines through Win32 Visual C++ function calls under Windows NT and 9x.

Date: August 7 1998
Rev: 0.00
Distribution: External
KDB Number: kdb-229
Author: SQP


Use the following function call:

EscapeCommFunction
The EscapeCommFunction function directs a specified communications device to
perform an extended function.

BOOL EscapeCommFunction(
HANDLE hFile, // handle to communications device
DWORD dwFunc // extended function to perform
);

Parameters:

hFile
Handle to the communications device. The CreateFile function returns
this handle.

dwFunc
Specifies the code of the extended function to perform. This parameter
can be one of the following values:
CLRDTR Clears the DTR (data-terminal-ready) signal.
CLRRTS Clears the RTS (request-to-send) signal.
SETDTR Sends the DTR (data-terminal-ready) signal.
SETRTS Sends the RTS (request-to-send) signal.
SETXOFF Causes transmission to act as if an XOFF character
has been received.
SETXON Causes transmission to act as if an XON character has
been received.
SETBREAK Suspends character transmission and places the
transmission line in a break state until the ClearCommBreak function is
called (or EscapeCommFunction is called with the CLRBREAK extended function
code). The SETBREAK extended function code is identical to the SetCommBreak
function. Note that this extended function does not flush data that has not
been transmitted.
CLRBREAK Restores character transmission and places the
transmission line in a nonbreak state. The CLRBREAK extended function code
is identical to the ClearCommBreak function.


Return Values
If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error
information, call GetLastError.

Remarks
Windows CE: Windows CE supports the following additional flags for the
dwFunc parameter:

SETIR
Sets the serial port in IR mode.
CLRIR
Sets port into normal serial mode.

QuickInfo
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winbase.h.
Import Library: Use kernel32.lib.

See Also
Communications Overview, Communication Functions, ClearCommBreak,
CreateFile, SetCommBreak

--- end kdb-0229 ---