Generate an analog signal on pin for milliseconds with a
duty cycle of 0 to 255.
A duty cycle of 255 corresponds to an
output value of 100%.
The IO direction of the pin will be set to output, the PWM pulse train is
output, and then the pin is set to tristate (input). If the pin is
connected to an RC filter, then the voltage will stay on the capacitor for a
period of time determined by the load.