Product Specs

Table Of Contents
42 NFCT Near field communication tag
Page
419
Activated
NFC (OTHER) (See activity)
GOIDLE
/COLLISION
DISABLE
DISABLE
NFC (ALL_REQ)
/ AUTOCOLRESSTARTED
/SELECTED
ACTIVATE
/ READY
IDLERU
IDLE
READY_A
NFC (SENS_REQ)
/ AUTOCOLRESSTARTED
NFC (ALL_REQ)
/ AUTOCOLRESSTARTED
SLEEP_A
DISABLE
SENSE
GOSLEEP
NFC (SLP_REQ)
ACTIVE_A
ENABLERXDATA
STARTTX
SENSE
SENSE_FIELD
STARTTX
/TXFRAMEEND
RECEIVE TRANSMIT
ACTIVATE
/RXFRAMEEND
/ RXERROR
Figure 118: NFC state diagram
42.2 Pin configuration
NFC uses two pins to connect the antenna.
These pins are shared with GPIOs, and the PROTECT field in the NFCPINS register in UICR defines the
usage of these pins and their protection level against excessive voltages. The content of the NFCPINS
register is reloaded at every reset.
When NFCPINS.PROTECT=NFC, a protection circuit will be enabled on the dedicated pins, preventing the
chip from being damaged in the presence of a strong NFC field. The GPIO function will be disabled on those
pins as well.
When NFCPINS.PROTECT=Disabled, the device will not be protected against strong NFC field damages
caught by a connected NFC antenna, and the NFCT peripheral will not operate as expected, as it will never
leave the DISABLE state.
The pins dedicated to the NFC antenna function will have some limitation when the pins are configured
for normal GPIO operation. The pin capacitance will be higher on those (refer to C
PAD_NFC
in the GPIO
Electrical Specification on page 154 below), and some increased leakage current between the two pins is
to be expected if they are used in GPIO mode, and are driven to different logical values. To save power the
two pins should always be set to the same logical value whenever entering one of the device power saving
modes. Please refer to I
NFC_LEAK
in GPIO Electrical Specification on page 154 for details.
42.3 EasyDMA
The NFC peripheral implements EasyDMA for reading and writing of data packets from and to the Data RAM
without CPU involvement.
The NFC EasyDMA utilizes one pointer called PACKETPTR for receiving and transmitting packets.
The EasyDMA can either read or write between the NFC peripheral and the RAM, but not at the same time.
The event RXFRAMESTART indicates that the EasyDMA has started writing to the RAM for a receive frame
and the event RXFRAMEND indicates that the EasyDMA has completed writing to the RAM. Similarly, the
event TXFRAMESTART indicates that the EasyDMA has started reading from the RAM for a transmit frame
and the event TXFRAMEND indicates that the EasyDMA has completed reading from the RAM. If a transmit
and a receive operation is issued at the same time, the transmit operation would be prioritized.
Starting a transmit operation while the EasyDMA has already started writing a receive frame to the RAM
will result in unpredictable behavior. Starting an EasyDMA operation whilst there is an ongoing EasyDMA
operation may result in unpredictable behavior. It is recommended to wait for the TXFRAMEEND or