I am developping an arduino shield that uses the uart lines (pin0/1) to communicate for the arduino.
The small problem with that is that i can’t upload a sketch to the arduino when the shield is on it, because uart lines are shared with usb (for arduino models with only one uart).
One solution, at least for avr boards, would be to disable the shield communication ( set RX to high z and ignore TX) when the reset line is active (low).
My question is : is this approach correct for all arduino models?
Do all arduino have an active low reset line, and do they all keep the line active during sketch upload?