The reset value of PSELRESET in nRF52840 why not is 0xffffffff, but 0x0012, and how can i change it?

[janho.cn]

Hi, I want to use the p0.18 as a GPIO without being connected to nRESET function. So I removed "CONFIG_GPIO_AS_PINRESET" from the define option in Keil. And then i found that the reset value of PSELRESET  was still been set as 0x0012  when I debugged the example project. Is the datasheet wrong? And then I try to set PSELRESET as: 

while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
NRF_UICR->PSELRESET[0] = 0xffffffff;
while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
NRF_UICR->PSELRESET[1] = 0xffffffff;

But it doesdn't work, the value of the PSELRESET  still is 0x0012.

So i want to known how to change the PSELRESET  to be  0xffffffff. Thank you.

[Hung Bui]

Hi,

You would need to erase the UICR to change the PSELRESET value to 0xFFFFFFFF. The write command can only change from bit 1 to bit 0. 

Make sure you back up other value in the UICR and re-write them back .