nRESET Pin floating in Deep Sleep which is causing wake up unintentionally

Question

Hello All,

I am having a trouble with the nReset Pin during Deep Sleep. The issue is that the board is waking up from Deep Sleep due to floating nReset Pin. I am using a nrf52480.

Before going to a Deep Sleep I am making this nReset Pin to the following configuration:-

    // Disable The GPIO needed for N_RESET_PIN
    nrf_gpio_cfg( N_RESET_PIN,
                         NRF_GPIO_PIN_DIR_INPUT,
                         NRF_GPIO_PIN_INPUT_CONNECT,
                         NRF_GPIO_PIN_PULLUP,
                         NRF_GPIO_PIN_S0S1,
                         NRF_GPIO_PIN_NOSENSE);

However when in deep sleep I manually checked that the nReset pin is in floating or Pull Up mode using a multimeter. Connected a multimeter (supposed to be very high impedance) to between Vdd and nRESET. Measured 0V as expected.

Then connected multimeter between gnd and nRESET. Measured 2.2V, however the sensor started to advertise.

As per this observation it is seen that the Pin configuration is going to NO_PULL from PULLUP while calling a Deep Sleep Function sd_power_system_off().

Why does this happen ?. Is there a work around for this ?.

Thanks,
Aswin :)

Jared · Answer

Hi

Before going to a Deep Sleep I am making this nReset Pin to the following configuration:-

    // Disable The GPIO needed for N_RESET_PIN
    nrf_gpio_cfg( N_RESET_PIN,
                         NRF_GPIO_PIN_DIR_INPUT,
                         NRF_GPIO_PIN_INPUT_CONNECT,
                         NRF_GPIO_PIN_PULLUP,
                         NRF_GPIO_PIN_S0S1,
                         NRF_GPIO_PIN_NOSENSE);

This is not quite how you enable PIN RESET on nRESET pin.

See the system_nRF52840.c file for a example on this:

    /* Configure GPIO pads as pPin Reset pin if Pin Reset capabilities desired. If CONFIG_GPIO_AS_PINRESET is not
      defined, pin reset will not be available. One GPIO (see Product Specification to see which one) will then be
      reserved for PinReset and not available as normal GPIO. */
    #if defined (CONFIG_GPIO_AS_PINRESET)
        if (((NRF_UICR->PSELRESET[0] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Connected << UICR_PSELRESET_CONNECT_Pos)) ||
            ((NRF_UICR->PSELRESET[1] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Connected << UICR_PSELRESET_CONNECT_Pos))){
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_UICR->PSELRESET[0] = 18;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_UICR->PSELRESET[1] = 18;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NVIC_SystemReset();
        }
    #endif

nRESET Pin floating in Deep Sleep which is causing wake up unintentionally

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