Texas Instruments TRF7970A Instruction Manual page 13

www.ti.com
The transmitter supports OOK and ASK modulation with selectable modulation depth. The TRF7970A also
includes a data transmission engine that comprises low-level encoding for ISO15693, ISO14443A/B and
FeliCa. Included with the transmit data coding is the automatic generation of Start Of Frame (SOF), End
Of Frame (EOF), Cyclic Redundancy Check (CRC), or parity bits.
Several integrated voltage regulators ensure a proper power-supply noise rejection for the complete
reader system. The built-in programmable auxiliary voltage regulator V
20 mA to supply a microcontroller and additional external circuits within the reader system.
6.1.2 NFC Device Operation – Initiator
The desired system of operation (bit rate) is achieved by selecting the option bits in control registers in the
same way as for RFID reader operation. Also the communication to external MCU and data exchange is
identical.
The transmitting system comprises an RF level detector (programmable level) which is used for initial (or
response) RF collision avoidance. The RF collision avoidance sequence is started by sending a direct
command. If successful, the NFC initiator can send the data or commands, the MCU has loaded in the
FIFO register. The coding of this data is done by hardware coders either in ISO14443A/B format or in
FeliCa format. The coders also provide CRC and parity bits (if required) and automatically add preambles,
SOF, EOF, and synchronization bytes as defined by selected protocol.
The receiver system offers same analog features (AGC, AM/PM, bandwidth selection, etc.) as described
previously in RFID and NFC reader and writer description. The system comprises integrated decoders for
passive targets (ISO14443A/B tag or FeliCa) or active targets (ISO14443A/B reader or FeliCa). For all this
options, the system also supports framing including CRC and parity check and removal of SOF, EOF, and
synchronization bytes as specified by the selected protocol.
6.1.3 NFC Device Operation – Target
The desired system of operation (bit rate) is achieved by selecting the option bits in control registers in the
same way as for RFID reader or NFC initiator operation. Also the communication to external MCU and
data exchange is identical.
The activation of NFC target is done when a sufficient RF field level is detected on the antenna. The level
needed for wake-up is selectable and is stored in non-volatile register.
When the activation occurs, the system performs automatic power-up and waits for the first command to
be received. Based on this command, the system knows if it should operate as passive or active target
and at what bit rate. After activation, the receiver system offers the same analog features (for example,
AGC, AM/PM, and bandwidth selection) as in the case of an RFID reader.
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) to enable 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 internally forced high).
When the voltage supply system and the oscillator are started and are stable, 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 NFC TARGET
device. When the first command from the INITIATOR is received another IRQ sent with B6 (RX start) set
Copyright © 2011–2014, Texas Instruments Incorporated
Submit Documentation Feedback
Product Folder Links: TRF7970A
SLOS743K – AUGUST 2011 – REVISED APRIL 2014
(pin 32), is able to deliver up to
DD_X
Detailed Description
TRF7970A
13