Boy：請參考EscapeCommFunction
見BCB->Help->Windows SDK
引用線上說明如下：
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    Identifies 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:     Value        Meaning
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.     See Also
ClearCommBreak, CreateFile, SetCommBreak 
請參考！