NRF52840 nRESET pin

[Mike]

When pin AC13 is configured as an nRESET pin, is an internal pullup enabled?  I don't have an external pullup on the pin currently and our reset circuit works so it seems like it does, but I just want to confirm if that is by design.

[hmolesworth]

Yes, the pull-up is enabled; I assume the pull-up value is about 13k (standard pull-up) as I never found a separate specification

[Mike]

Also, it seems that during reset the output of REG0 goes to 0 volts.  We are using a battery hooked up to VDDH, I just want to confirm that this is the expected operation.

[hmolesworth]

That sounds worrying, need Nordic Engineer input for this .. if Reg0 indeed goes to 0 volts, then the power for the core including the reset pin itself will disappear leading to a potential oscillating condition once the core recovers ..

The other issue with the reset pull-up is that extended shelf life is not possible by simply holding down a reset button as the discharge current is high given 13k pull-up resistance. I only mention this as I came across a case where the user was doing just that, taping down the reset button (not the nRF52840 though). They changed to system off with another pin used as wake-up.

[Mike]

My mistake, it looks like it drops down to 1.8V before being initialized back to 3.3V.  Is there a way to program it so that REG0 is permanently 3.3V?

[Øyvind]

Hello, 

You can read more about how to configure the power supply in the Power and Clock Management Chapter. The REG0 output is available in High Voltage mode, and configured in the REGOUT0 register.

Kind regards,
Øyvind