ZHCS363L August 2011 – March 2017 TRF7970A
PRODUCTION DATA.
When used as the NFC target, the chip is typically in a power down or standby mode. If EN2 = H, the chip keeps the supply system on. If EN2 = L and EN = L the chip is in complete power down. To operate as NFC target or card emulator, the MCU must load a value different from zero (0) in Target Detection Level register (b0-b2) which enables the RF measurement system (supplied by VEXT, so it can operate also during complete power down and consumes only 3.5 µA). The RF measurement constantly monitors the RF signal on the antenna input. When the RF level on the antenna input exceeds the level defined in the in Target Detection Level register, the chip is automatically activated (EN is internal forced high). The typical RF value that causes power-up for each value of B0 to B2 and the function of Target Detection Level register is listed in Table 6-15.
NFC Target Detection Level Register (0x18) – defines level for RF level for wake-up and gives information of NFCID size. This register is directly supplied by VEXT to ensure data retention during complete power down.
BIT | SIGNAL NAME | FUNCTION | COMMENTS |
---|---|---|---|
B7 | Id_s1 | NFCID1 size used in 106 kbps passive target SDD | |
B6 | Id_s0 | ||
B5 | Sdd_en | 1 = Enables internal SDD protocol | Automatic SDD using internal state machine and ID stored in NFCID Number register(1) |
B4 | N/A | ||
B3 | Hi_rf | Extended range for RF measurements | |
B2 | Rfdet_h2 | RF field level required for system wake-up. If all bits are 0, the RF level detection is switched off. | Comparator output is displayed in NFC Target Protocol register B7 (rf_h) |
B1 | Rfdet_h1 | ||
B0 | Rfdet_h0 |
Default: reset to 00 at POR on VEXT (not on POR based on VDD_X), not reset at EN = 0
B0 B1 B2 | 000 | 001 | 010 | 011 | 100 | 101 | 110 | 111 | |
---|---|---|---|---|---|---|---|---|---|
B3 = 0 | RF Vpp | Not active | 480 mV | 350 mV | 250 mV | 220 mV | 190 mV | 180 mV | 170 mV |
B3 = 1 | RF Vpp | Not active | 1500 mV | 700 mV | 500 mV | 450 mV | 400 mV | 320 mV | 280 mV |
When the voltage supply system and the oscillator are started and is stable, the osc_ok goes high (B6 of RSSI Level and Oscillator Status register) and IRQ is sent with bit B2 = 1 of IRQ register (field change). Bit B7 NFC Target Protocol in register directly displays the status of RF level detection (running constantly also during normal operation). This informs the MCU that the chip should start operation as an NFC TARGET device.
When the first command from the INITIATOR is received another IRQ sent with B6 (RX start) set in IRQ register. The MCU must set EN = H (confirm the power-up) in the time between the two IRQs as the internal power-up ends after the second IRQ. The type and coding of the first initiator (or reader in the case of a card emulator) command define the communication protocol type which the target must use. So the communication protocol type is available in the NFC Target Protocol register immediately after receiving the first command. The coding of the NFC Target Protocol register is described next.
NFC Target Protocol Register (0x19) – displays the bit rate and protocol type (active or passive) transmitted by initiator in the first command. It also displays the comparator outputs of both RF level detectors.
BIT | NAME | FUNCTION | DESCRIPTION |
---|---|---|---|
B7 | Rf_h | 1 = RF level is above the set wake-up level | The wake-up level is defined by bits b0-b3 of NFC Target Detection Level register |
B6 | Rf_l | 1 = RF level is above the RF collision avoidance level | The collision avoidance level is defined by bits b0-b2 of NFC Low Field Detection Level register |
B5 | N/A | ||
B4 | FeliCa | 1 = FeliCa type 0 = ISO/IEC 14443 A type |
The first initiator command had physical level coding like FeliCa or like ISO/IEC 14443 A |
B3 | Pas106 | Passive target 106 kbps or card emulation | The first initiator/reader command was SENS_REQ or ALL_REQ |
B2 | Pas14443B | Card emulation ISO/IEC 14443 B | The first reader command was of ISO/IEC 14443 B type |
B1 | Nfcbr1 | Bit rate of first received command | 00 = N/A 01 = 106 kbps 10 = 212 kbps 11 = 424 kbps |
B0 | Nfcbr0 |
Default: reset to 00 at POR and EN = L. B0 to B4 are automatically reset after MCU read operation. B6 and B7 continuously display the RF level comparator outputs.
Based on the first command from INITIATOR following actions are taken:
Table 6-18 shows the function of the IRQ Status register in NFC and card emulation. This register is preset to 0 at POR = H or EN = L and at each write to ISO Control. It is also automatically reset at the end of read phase. The reset also removes the IRQ flag.