code: def sense_ttb(self, target):
          
          log.debug("polling for NFC-B technology")
  
          if target.brty not in ("106B", "212B", "424B"):
              message = "unsupported bitrate {0}".format(target.brty)
              raise nfc.clf.UnsupportedTargetError(message)
  
          self.chipset.in_set_rf(target.brty)
          self.chipset.in_set_protocol(self.chipset.in_set_protocol_defaults)
          self.chipset.in_set_protocol(initial_guard_time=20, add_sof=1,
                                       check_sof=1, add_eof=1, check_eof=1)
  
          sensb_req = (target.sensb_req if target.sensb_req else
                       bytearray.fromhex("050010"))
  
          log.debug("send SENSB_REQ " + hexlify(sensb_req))
          try:
              sensb_res = self.chipset.in_comm_rf(sensb_req, 30)
          except CommunicationError as error:
              if error != "RECEIVE_TIMEOUT_ERROR":
                  log.debug(error)
              return None
  
          if len(sensb_res) >= 12 and sensb_res[0] == 0x50:
              log.debug("rcvd SENSB_RES " + hexlify(sensb_res))
              return nfc.clf.RemoteTarget(target.brty, sensb_res=sensb_res)
docs: Sense for a Type B Target is supported for 106, 212 and 424
          kbps. However, there may not be any target that understands the
          activation command in other than 106 kbps.