A stylus pen is disclosed that can detect touch signals from a digitizer and dynamically determine which digitizer (e.g., make/model) generated the touch signals. The stylus pen can then switch to one of a plurality of candidate protocols, without interaction from the user, so as to communicate with the digitizer. The digitizer need not explicitly communicate what protocol it supports to the stylus pen. Rather, the stylus pen analyzes the digitizer waveforms and compares the waveforms to known signatures to determine which digitizer is being used. The stylus pen can then dynamically set a protocol used to communicate with the digitizer that matches the protocol expected by the digitizer.