5.1 Active Communication

The TRF7970A ISO Control register (0x01) sets the modulation of the transceiver RF field when is in initiator mode and the bit rate to load modulate when it is in target mode. The NFC active and passive initiator (bit 5 = 1 and bit 2 = 1) for baud rates of 212 kbps and 424 kbps, can be achieved by initializing the transceiver as a NFC-F reader (Bit 5 = 1 and bits 4-0 = 0x12 (212 kbps) or 0x13 (424 kbps)). Each time the transceiver finishes sending a command while being an initiator or target, the transceiver must:

1. Turn off the field by modifying the ISO Control register → 0x21 (passive target).
2. Write to RX Special Setting register (0x0A) → 0x80 (band-pass filter set for 110 kHz to 570 kHz)
3. Write to Adjustable FIFO IRQ Levels register (0x14) → 0x0F (IRQ triggered when there are 96 bytes in FIFO during RX or 32 bytes during TX)