chaff wrote:

There's a transistor inverter shown for IO3's output on the circuit diagram. 100% PWM will result in the transistor 'on' all the time and the output will be low ( the load would be connected between +5v and the IO3 output ). Unless you put a pull-up resistor between 5v and the output pin your meter won't see the IO3 pin float to +5v when PWM is 0% output.