nRF5340 NFC/GPIO pins during reset

RE: nRF5340 NFC/GPIO pins during reset

Samuel Carey — Fri, 06 Nov 2026 21:37:39 GMT

Thank you for the reply. So to clarify: if I set the PROTECT to disabled and then power cycle the 5340, will the pins reboot as exclusively GPIO or will there be a short time on boot that they will use the NFC inputs?

RE: nRF5340 NFC/GPIO pins during reset

Amanda Hsieh — Fri, 06 Nov 2026 21:26:56 GMT

When UICR.NFCPINS.PROTECT=NFC, the PS describes a protection path that ties NFC1 and NFC2 together if their differential voltage exceeds ~2 V, and states GPIO is disabled on those pads (see NFCT — Pin configuration); the PS gives no tolerance on that ~2 V, so 1.8 V differential cannot be assumed safe. Vsense (~1.2 Vp differential, high-Z in sense mode,see NFCT electrical spec) is carrier/field detect, not the same as that clamp. With PROTECT=NFC, do not treat the pads as GPIO inputs for strapping; external pulls are not a supported, specified way to set a digital level (and they still electrically load the NFC pad). For GPIO or reliable digital behavior, use PROTECT=Disabled (and accept loss of NFC antenna + protection per PS) or another GPIO. See NFCPINS and NFCT — Pin configuration.

RE: nRF5340 NFC/GPIO pins during reset

Samuel Carey — Thu, 05 Nov 2026 21:08:41 GMT

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?

RE: nRF5340 NFC/GPIO pins during reset

Samuel Carey — Thu, 05 Nov 2026 21:07:03 GMT

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

RE: nRF5340 NFC/GPIO pins during reset

Amanda Hsieh — Thu, 05 Nov 2026 20:50:00 GMT

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.