Are UICR OTP registers eraseable with nrfjprog's --sectoranduicrerase?

[nwl_at_whisper]

Hello,

The documentation for the nRF5340 says that the UICR OTP registers can only be written to a non-0xFFFF value a single time:
> Can only be written to a non 0xFFFF value once.

I am wondering if this OTP can be reset to factory default via nrfjprog, or if it is truly OTP and cannot be reset at all once it is written. The nrfjprog manual: https://infocenter.nordicsemi.com/pdf/nRF5x_Command_Line_Tools_v1.0.pdf does not specify.

Thanks,

Nick

[Einar Thorsrud]

Hi Nick,

The --sectoranduicrerase option does not really make sense on the nRF53 series, as the only way you can erase the UICR is by an erase all (for instance a "nrfjprog --recover"). That said, when you do an erase all, that erases both the UICR and OTP. In other words, it is not true OTP, but rather an emulated OTP.

Specifically, the OTP in the nRF53 allows a single write per half-word. This works so that if all bits in a half-word is '1', a write is allowed. If any of the bits are '0' that means it has already been written to, and a write is not allowed. A full chip erase will reset everything back to all '1' though, including the OTP region.

Einar