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SLOS743L – AUGUST 2011 – REVISED MARCH 2017
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Detailed Description
Copyright © 2011–2017, Texas Instruments Incorporated
(1)
See the
for details on automatic SDD dependencies.
6.12 Special Direct Mode for Improved MIFARE™ Compatibility
See
Using Special Direct Mode With the TRF7970A
6.13 NFC Modes
6.13.1 Target
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
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.
Table 6-15. NFC Target Detection Level Register
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 V
DD_X
), not reset at EN = 0
Table 6-16. Bits B0 to B3 of the NFC Target Detection Level Register
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.
