I have connected a led to the DTR line of the serial port just for testing purposes.

Turning the led on/off works just fine with the EscapeCommFunction() function which sets or clears the DTR line.

However, there is a problem. As soon as the serial port is opened with CreateFile(), there is a short pulse on the DTR line which causes the led to blink very shortly. Does someone knows how to prevent this startup pulse to occur?

Thanks in advance.

m_hPort = CreateFile(
		portName,						// Pointer to the name of the port
		GENERIC_READ | GENERIC_WRITE,	// Access (read/write) mode
		0,								// 0, serial ports can not be shared
		NULL,							// Pointer to the security attribute
		OPEN_EXISTING,					// How to open the serial port 
		0,								// Port attributes 
		NULL);							// Handle to port with attribute to copy

	// If it fails to open the port, return false.
	if (m_hPort == INVALID_HANDLE_VALUE) 
		return false;
	return true;