code: def power_down(self, wakeup_enable):
          
          wakeup_set = 0
          for i, src in enumerate(self.power_down_wakeup_sources):
              if src in wakeup_enable:
                  wakeup_set |= 1 << i
          data = self.command(0x16, chr(wakeup_set), timeout=0.1)
          if data[0] != 0:
              self.chipset_error(data)
docs: Send the PowerDown command to put the PN531 (including the
          contactless analog front end) into power down mode in order to
          save power consumption. The *wakeup_enable* argument must be a
          list of wake up sources with values from the
          :data:`power_down_wakeup_sources`.