nRF5340 NFC/GPIO pins during reset

[Samuel Carey]

During reset and initialization are the NFC pins configured as GPIO or as NFC?

If they are in NFC mode can you clarify if they have any special behavior on boot (pulls, impedance to ground, etc)?

I have found a note that the nRF52832 NFC Pins default to NFC but it is unclear if this is true of the 5340.

[Amanda Hsieh]

Hi Samuel, 

When UICR.NFCPINS is at its documented reset value (0xFFFFFFFF), PROTECT is NFC, the NFC protection path is enabled, and the pads are not usable as normal GPIOs. 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 protection circuit will short the two pins together if voltage difference exceeds approximately 2V. The GPIO function on those pins will also be disabled. See PS nRF5340 NFC / Pin configuration 

Regards,
Amanda H.

[Samuel Carey]

You say "approximately 2V". How approximately? Is 1.8V close enough that it may sometimes short?

[Samuel Carey]

Similarly, are the NFC pins effectively floating inputs? If I have an external input with a weak pull down, will the NFC defeat the pull-down and initialize high?