Error opening serial port COM5

Okay - I've reinstalled the IDE (Arduino 1.6.8 - 1.6.9 has install errors) on my PC (Windows10, 64-bit) and still get the error when I upload the code to an Arduino UNO. The Board is identified in the IDE as an Arduino/Genuino UNO (which it is), connected to port "COM5(Arduino/Genuino Uno)". I'm using the programmer "AVRISP mkII" to do the updates. Compiles fine, then the LED's flash and the "Port Busy" error shows up.
I am connected to digital pins 0 and 1 in the sketch - is this a problem? If so, is there any way to override the default RX/TX mode to allow the pins to be used as general I/O?

The pins 0 and 1 are used for serial communication and should not be used for any other function. Try modifying the code and change the pins. That should proabably help you. :slight_smile:

You can change the serial pins with the “softserial” libs.

Look it up for specifics and examples.

It seems the hardware won't allow my configuration - I need just one more I/O port. So I'll have to use a different board. Thanks for the suggestions. The clearest explanation was in the schematics - TX and RX are connected to the UART chip via resistors. No chance to reconfigure without cutting traces on the board.