Port 201  -  Game controller

        A read should be preceded by an initializing write of any
        data. The write will start the timing for the resistive
        values.


        Digital inputs:
          (1=no contact, 0=pressed)

          1xxx xxxx  Joystick B, button 2
          x1xx xxxx  Joystick B, button 1
          xx1x xxxx  Joystick A, button 2
          xxx1 xxxx  Joystick A, button 1


        Resistive inputs
          Lenght of pulse determined by 0-100K ohm resistive load.
          Time=24.2 ms + (0.011 ms*resistance)

          xxxx 1xxx  Joystick B, y-coordinate
          xxxx x1xx  Joystick B, x-coordinate
          xxxx xx1x  Joystick A, y-coordinate
          xxxx xxx1  Joystick A, x-coordinate