Texas Instruments TRF7970A Instruction Manual page 49

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Bit Signal Name
B7 Id_s1
B6 Id_s0
B5 Sdd_en
B4
B3 Hi_rf
B2 Rfdet_h2
B1 Rfdet_h1
B0 Rfdet_h0
(1) Refer to the device errata (SLOZ011) for details on automatic SDD dependencies.
Default: reset to 00 at POR on VEXT (not on POR based on V
Table 6-16. Bits B0 to B3 of the NFC Target Detection Level Register
b0 B1 B2
B3 = 0 RF Vpp Not active
B3 = 1 RF Vpp Not active
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 tag 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 Signal Name
B7 Rf_h
B6 Rf_l
B5
B4 FeliCa
B3 Pas106
B2 Pas14443B
B1 Nfcbr1
B0 Nfcbr0
Copyright © 2011–2014, Texas Instruments Incorporated
Table 6-15. NFC Target Detection Level Register
Function
NFCID1 size used in 106 kbps passive target SDD
1 = Enables internal SDD protocol
N/A
Extended range for RF measurements
RF field level required for system wake-up. If all
bits are 0, the RF level detection is switched off.
000 001 010
480 mV 350 mV
1500 mV 700 mV
Table 6-17. NFC Target Protocol Register
Function
1 = RF level is above the set wake-up level
1 = RF level is above the RF collision avoidance
level.
N/A
1 = FeliCa type
0 = ISO14443A type
Passive target 106 kbps or tag emulation
Tag emulation ISO14443B
Bit rate of first received command
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SLOS743K – AUGUST 2011 – REVISED APRIL 2014
Automatic SDD using internal state machine and ID
stored in NFCID Number register
Comparator output is displayed in NFC Target
Protocol register B7 (rf_h)
), not reset at EN = 0
DD_X
011 100 101
250 mV 220 mV 190 mV
500 mV 450 mV 400 mV
The wake-up level is defined by bits b0-b3 of NFC
Target Detection Level register
The collision avoidance level is defined by bits b0-
b2 of NFC Low Field Detection Level register
The first initiator command had physical level
coding like FeliCa or like ISO14443A
The first initiator/reader command was SENS_REQ
or ALL_REQ
The first reader command was of ISO14443B type
00 = N/A
01 = 106 kbps
10 = 212 kbps
11 = 424 kbps
TRF7970A
TRF7970A
Comments
(1)
110 111
180 mV 170 mV
320 mV 280 mV
Comments
Detailed Description 49