User's Manual

TRF7970A
SLOS743K –AUGUST 2011–REVISED APRIL 2014 www.ti.com
Figure 6-32. RX Sequence on I/O_6 in DM0 (Analog Capture)
Step 7: Terminating Direct Mode 0
After the EOF is received, data transmission is over, and Direct Mode 0 can be terminated by sending a
Stop Condition (in the case of SPI, make the Slave Select go high). The TRF7970A is returned to default
state.
6.11 Special Direct Mode for Improved MIFARE™ Compatibility
See the application report TRF7970A Firmware Design Hints (SLOA159).
6.12 NFC Modes
6.12.1 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 Tag 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.
48 Detailed Description Copyright © 2011–2014, Texas Instruments Incorporated
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