System Off & GPIO pull-up / pull-down

[Jason De Lorme]

If the nRF51 chip is in System Off state, do the GPIO pins retain the pull-ups or pull-downs? If so, what value do they have and how much current can they sink or source?

This post gets close to answering, but not exactly: devzone.nordicsemi.com/.../

[Stefan Birnir Sverrisson]

Hi Jason

All GPIO configuration is retained is System Off. Perhaps you could benefit from looking at the system-off-wakeup-on-gpio example which shows how pins are configured to wake up from System Off.

The default sink/source current is 0.5mA. This can be configured however by writing to the PIN_CNF register for a specfic pin, bits D, see section 13.2.8 in nRF51 Series Reference Manual v2.1. To see specifically how this is done in code, look at the definition for the nrf_gpio_cfg_sense_input function in nrf_gpio.h in the above linked example. Standard drive is 0.5mA max, high drive is 5mA max. Max combined drive for all GPIO's is 15mA.

[Jason De Lorme]

Thank you, Stefan. To be clear, when the chip is in System Off and I have previously configured pull-down on a pin, will that pin have 0 volts (LOW) or will it float? Specifically I'm looking at controlling an external device that needs the pin to be pulled low when the chip is in System Off and I need to know if we have to add our own pull down resistor on our board or if we could rely on the nRF51 pull down resistor?

Thank you!

[Stefan Birnir Sverrisson]

Yes, the pin will be pulled low in System Off as the GPIO configuration is retained in System Off