Reads back the PID constants stored on the Grizzly.

def read_pid_constants(self):
        """Reads back the PID constants stored on the Grizzly."""
        p = self._read_as_int(Addr.PConstant, 4)
        i = self._read_as_int(Addr.IConstant, 4)
        d = self._read_as_int(Addr.DConstant, 4)
        
        return map(lambda x: x / (2 ** 16), (p, i, d))