code: def read_passive_target(self, card_baud=PN532_MIFARE_ISO14443A, timeout_sec=1):
          
          # Send passive read command for 1 card.  Expect at most a 7 byte UUID.
          response = self.call_function(PN532_COMMAND_INLISTPASSIVETARGET,
                                        params=[0x01, card_baud],
                                        response_length=17)
          # If no response is available return None to indicate no card is present.
          if response is None:
              return None
          # Check only 1 card with up to a 7 byte UID is present.
          if response[0] != 0x01:
              raise RuntimeError('More than one card detected!')
          if response[5] > 7:
              raise RuntimeError('Found card with unexpectedly long UID!')
          # Return UID of card.
          return response[6:6+response[5]]
docs: Wait for a MiFare card to be available and return its UID when found.
          Will wait up to timeout_sec seconds and return None if no card is found,
          otherwise a bytearray with the UID of the found card is returned.