Directs a specified communications device to perform an extended function.

BOOLEAN EscapeCommFunction(
  COMMHANDLE hComm,  // handle to communications device
  DWORD dwFunc       // extended function to perform
);

Parameters

hComm

[in] Handle to the communications device. OpenComm returns this handle.

dwFunc

[in] Specifies the code of the extended function to perform. This parameter can be one of the following values:

Value	Description
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 ClearCommBreak is called (or EscapeCommFunction is called with the CLRBREAK extended function code). The SETBREAK extended function code is identical to SetCommBreak. Note that this extended function does not flush data that is not yet 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

Non-zero

Success.

0 (zero)

Failure. To determine the status, call GetLastRtError.

Status

E_CONTEXT

Attempt to change flow control line when flow control enabled.

E_DISCONNECTED

COMM channel is closed

E_PARAM

Invalid parameter

Requirements