Texas Instruments TRF7970A Manual page 51

www.ti.com
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
B7 Rf_h 1 = RF level is above the set wake-up level
B6 Rf_l 1 = RF level is above the RF collision avoidance level
B5 N/A
1 = FeliCa type
B4 FeliCa
0 = ISO/IEC 14443 A type
B3 Pas106 Passive target 106 kbps or card emulation
B2 Pas14443B Card emulation ISO/IEC 14443 B
B1 Nfcbr1
Bit rate of first received command
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:
• If the first command is SENS_REQ or ALL_REQ, the TARGET must enter the SDD protocol for 106
kbps passive communication. If bit B5 in NFC Target Detection Level register is not set, the MCU
handles the SDD and the command received is send to FIFO. If the RF field is turned off (B7 in the
NFC Target Protocol register goes low) at any time, the system sends an IRQ to the MCU with bit B2
(RF field change) in the IRQ register set high. This informs the MCU that the procedure was aborted
and the system must be reset. The clock extractor is automatically activated in this mode.
• If the command is SENS_REQ or ALL_REQ and the card emulation bit in the ISO Control register is
set, the system emulates an ISO/IEC 14443 A card. The procedure does not differ from the one
previously described for a passive target at 106 kbps. The clock extractor is automatically activated in
this mode.
• If the first command is a SENSF_REQ, the system becomes a TARGET in passive communication
using 212 kbps or 424 kbps. The SDD is relatively simple and is handled by the MCU directly.
• If the first command is ATR_REQ, the system operates as an active TARGET using the same
communication speed and bit coding as used by the INITIATOR. Again, all of the replies are handled
by the MCU. The MCU should check for collision avoidance by checking the external RSSI as
described in Section
MCU can begin the process to send the reply.
• If the first command is coded as ISO/IEC 14443 B and the card emulation bit is set in the ISO Control
register, the system enters ISO/IEC 14443 B emulator mode. The anticollision must be handled by the
MCU, and the chip provides all physical level coding, decoding, and framing for this protocol.
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.
Copyright © 2011–2017, Texas Instruments Incorporated
Table 6-17. NFC Target Protocol Register
FUNCTION
6.5.1.2. When no RF field is detected from the external RSSI result, then the
Submit Documentation Feedback
Product Folder Links:
SLOS743L – AUGUST 2011 – REVISED MARCH 2017
DESCRIPTION
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 ISO/IEC 14443 A
The first initiator/reader command was
SENS_REQ or ALL_REQ
The first reader command was of ISO/IEC 14443 B
type
00 = N/A
01 = 106 kbps
10 = 212 kbps
11 = 424 kbps
TRF7970A
TRF7970A
Detailed Description 51