code: def duty_cycle(self):
          
          pwm = self._pca.pwm_regs[self._index]
          if pwm[0] == 0x1000:
              return 0xffff
          return pwm[1] << 4
docs: 16 bit value that dictates how much of one cycle is high (1) versus low (0). 0xffff will
             always be high, 0 will always be low and 0x7fff will be half high and then half low.