nRF52840 Preview DK v0.9.x

NFC antenna interface

The nRF52840 Preview DK board supports a near field communication (NFC) tag.

NFC-A listen mode operation is supported on the nRF52840 SoC. The NFC antenna input is available on connector J5 on the nRF52840 Preview DK board.

Figure 1. NFC antenna connector
NFC antenna connector on the nRF52840 Preview Development Kit board

NFC uses two pins, L24 (NFC1) and J24 (NFC2), to connect the antenna. These pins are shared with GPIOs (P0.09 and P0.10) and the PROTECT field in the NFCPINS register in UICR defines the usage of these pins and their protection level against abnormal voltages. The content of the NFCPINS register is reloaded at every reset.

Important: The NFC pins are enabled by default.

NFC can be disabled and GPIOs enabled by defining the CONFIG_NFCT_PINS_AS_GPIOS variable in the project settings. This can be done by defining the preprocessor symbol in Keil. Go to: Project > Options for Target > C/C++ > Preprocessor Symbols > Define, and add the CONFIG_NFCT_PINS_AS_GPIOS variable after NRF52. This functionality can be removed by doing a nRFjprog --recover.

Pins L24 and J24 are by default configured to use the NFC antenna, but if they are needed as normal GPIOs, R44 and R46 must be NC and R43 and R45 must be shorted by 0R.

Figure 2. NFC input schematic
nRF52840 Preview Development Kit NFC input schematic