Product Specs

42 NFCT — Near field communication tag
Page
418
Wake-on-field is supported in SENSE mode while the device is either in System OFF or System ON mode.
When the antenna enters an NFC field, an event will be triggered notifying the system to activate the
NFC functionality for incoming frames. In System ON, if the energy detected at the antenna increases
beyond a threshold value, the module will generate a FIELDDETECTED event. The module will generate a
FIELDLOST event when the quality or strength of the field no longer support NFC communication. Please
refer to NFCT Electrical Specification on page 436 for the Low Power Field Detect threshold values.
In system OFF, the NFC Low Power Field Detect function can wake the system up through a reset. The NFC
bit in register RESETREAS on page 85 will be set as cause of the wake-up.
If the system is put into system OFF mode while a field is already present, the NFC Low Power Field Detect
function will wake the system up right away and generate a reset.
Note that as a consequence of reset, NFC is disabled, so the reset handler will have to activate NFC again
and set it up properly.
The HFXO must be running before the NFC peripheral goes into ACTIVATED state. Note that the NFC
peripheral calibration is automatically done on ACTIVATE task. The HFXO can be turned off when the NFC
peripheral goes into SENSE mode. The shortcut FIELDDETECTED_ACTIVATE can be used when the
HFXO is already running while in SENSE mode.
Outgoing data will be collected from RAM with the EasyDMA function and assembled according to the
TXD.FRAMECONFIG register. Incoming data will be disassembled according to the RXD.FRAMECONFIG
register and the data section in the frame will be written to RAM via the EasyDMA function.
The NFC peripheral includes a frame timing controller that can be used to accurately control the inter-frame
delay between the incoming frame and a corresponding outgoing frame. It also includes optional CRC
functionality.
The NFC peripheral has a set of different states. The module can change state by triggering a task, or when
specific operations are finalized. Events and tasks allow software to keep track of and change the current
state.
See Figure 117: NFC block diagram on page 417 and Figure 118: NFC state diagram on page 419 for
more information.
Notes:
• FIELDLOST event will not be reflected in the state machine (for instance by going back to the DISABLE
state), it is up to software to decide on the actions to take when a field lost occurs.
• FIELDLOST event is not generated in SENSE mode.
• FIELDDETECTED event is generated only on the transition from FIELDLOST event to energy
detected by the NFC peripheral. So, sending SENSE task while field is still present does not generate
FIELDDETECTED event.
• If the FIELDDETECTED event is cleared before sending the ACTIVATE task, then the FIELDDETECTED
event shows up again after sending the ACTIVATE task. The shortcut FIELDDETECTED_ACTIVATE can
be used to avoid this condition.