ISO IEC 21481-2021 pdf Information technology — Telecommunications and information exchange between systems — Near field communication interface and protocol 2 (NFCIP-2)

7 External RF field detection During external RF field detection, an NFCIP-2 device shall, for a period of T IDT + n × T RFW , detect external RF fields at fc with a value higher than H THRESHOLD and shall not generate an RF field. T IDT , T RFW , n and H THRESHOLD are specified in ISO/IEC 18092.
9 Mode selection and switching This clause specifies the procedure, which is comprised of mode selection and the sequence for mode switching, for NFCIP-2 devices to switch to the NFC mode, the PCD mode, the PICC mode or the VCD mode. Initially the NFCIP-2 device shall not generate its RF field prior to the procedure. The mode is selected prior to the execution of the following sequence. When repeating the procedure, the NFCIP-2 device may stop generating its RF field to change the communication modes. The NFCIP-2 device shall execute the following sequence: a) If the PICC mode has been selected, the NFCIP-2 device shall not generate its RF field and shall switch to the PICC mode. b) If the NFC mode has been selected, the NFCIP-2 device shall switch to the NFC mode. c) If the PCD mode has been selected, and if the NFCIP-2 device 1) generates its RF field, it shall switch to the PCD mode; 2) does not generate its RF field, it shall perform external RF field detection as specified in Clause 7. If no external RF field is detected, the NFCIP-2 device shall generate an RF field as specified in Clause 8 and switch to the PCD mode. Otherwise, the NFCIP-2 device shall recommence the procedure. d) If the VCD mode has been selected, and if the NFCIP-2 device 1) generates its RF field, it shall switch to the VCD mode;2) does not generate its RF field, it shall perform external RF field detection as specified in Clause 7. If no external RF field is detected, the NFCIP-2 device shall generate an RF field as specified in Clause 8 and switch to the VCD mode. Otherwise, the NFCIP-2 device shall recommence the procedure. Figure 2 illustrates the procedure.