In general, is the output voltage from a GPIO pin of most microcontrollers always regulated? Is it always 3.3V or whatever?
A lot of microcontrollers, the VIN is suppose to be above 3.3V with some bit of margin. And the digital output voltage from the GPIO pin seems to be just under 3.3V or so. But then I see BLE modules that use coin cells and the VIN can be 2.5 to 4.8V, and I don't know if the GPIO output floats down if VIN starts going down.
I don't really know what happens between VIN and the output pin, basically. What's all that stuff in there?