User's Manual

TRF7970A
www.ti.com SLOS743K –AUGUST 2011–REVISED APRIL 2014
6.14.3.3.10 NFC Target Protocol Register (0x19)
This register is used (when read) to display the bit rate and protocol type when an NFC/RFID
Initiator/Reader is presented. An example use of this scenario would be when the TRF7970A is placed
into card emulation (Type A or Type B) and another TRF7970A or NFC device (polling for other NFC
devices) is presented to the TRF7970A in card emulation mode. The IRQ indicates that a field was
detected (IRQ Status = 0x04) or that Auto SDD has completed (IRQ Status = 0x08, if configured for
AutoSDD).
If Auto SDD is set and 0x04 is returned in IRQ status, then this register can be read out to see which
commands are coming in for gaining knowledge of the polling cycle sequence. Then, when the correct first
matching command (that is, REQA or REQB) is issued from Reader or Initiator, if AutoSDD is set, the IRQ
fires and the IRQ Status is 0x08, indicating completion of the SDD. The next IRQ should return 0x40 as
status, the Register 0x19 can be checked to make sure it is correct value (that is, 0xC9 for Type A at 106
kpbs or 0xC5 for Type B at 106 kbps) indicating there are bytes in the FIFO and a read of the FIFO status
indicates how many bytes to read out. For example, after AutoSDD is completed, there are four bytes in
the FIFO, and these should be the RATS command coming in from the reader, which the MCU controlling
the TRF7970A in Card Emulation mode must respond to. If AutoSDD is not set, as another example with
the TRF7970A in ISO14443B Card Emulation mode, then the field detect happens as previously described
and IRQs also fire to indicate RX is complete (0x40). This register must be checked and compared against
case statement structure that is set up for the value of this register to be 0xC5, indicating that an
ISO14443B command at 106 kbps was issued. When this register (0x19) is 0xC5, then the FIFO Status
can be read and should hold a value of 0x03, and when read, be the REQB command (0x05, 0x00, 0x00);
the controlling MCU must respond with the ATQB response. The next steps for either of these examples
follow the revelent portions of the ISO14443-3 or -4 standards, then the NFC Forum specifications,
depending on the system use case or application.
Table 6-53. NFC Target Protocol Register (0x19)
Function: Displays the bit rate and protocol type (active or passive) transmitted by initiator in first command. It also displays the comparator
outputs of both RF level detectors.
Default: 0x00 at POR = H and EN = L. B0 to B4 are automatically reset after MCU continuous read operation. B6 and B7 continuously
display the RF level comparator outputs.
Bit Name Function Description
RF level is above the wake- The wakeup level is defined by bits B0 to B2 in the NFC Target Detection Level
B7 Rf_h
up level setting register (0x18)
RF level is above the RF
The collision avoidance level is defined by bits B0 – B2 in the register 0x16
B6 Rf_l collision avoidance level
(NFC Low Field Detection Level)
setting
B5 Reserved Reserved Reserved
1 = FeliCa
B4 FeliCa The first initiator command had physical level coding of FeliCa or ISO14443A
0 = ISO14443A
Passive target at 106 kbps
B3 Pas_106 The first initiator/reader command was SENS_REQ or ALL_REQ
or transponder emulation
ISO14443B transponder
B2 Pas_14443B The first reader command was ISO14443B
emulation
B1 NFCBR1 00 = Reserved
Bit rate of first received 01 = 106 kbps
command 10 = 212 kbps
B0 NFCBR0
11 = 424 kbps
Copyright © 2011–2014, Texas Instruments Incorporated Detailed Description 71
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