The WriteRealPort method starts writing any data to real serial port at any time.  

LONG WriteRealPort(
 BYTE* Buf , // data buffer
 LONG* Count// number of bytes to read

  Buf – [out] Pointer to the buffer that receives the data read from the serial port.         Count – [in] Pointer to number of bytes to be read from the port.
Return Values
  If the function succeeds, the return value is TRUE. If the port is already being sniffed or does not exist, the return value is FALSE.