SAADC VDD Measurement with nRF52833

Question

Hello, I am trying to measure the input voltage on an nRF52833 and it is not behaving as expected.

The following code is taken from here and works as expected on any nRF52832-based device I have tested, returning the correct board input voltage. When I try it on our nRF52833 board it returns 0.

Are there any changes to the SAADC configuration or register addresses that need to be accounted for when porting between the 832 and 833? Thank you in advance.

#include "nrf52833.h"
#include "nrf52833_bitfields.h"


uint16_t battery_sample_voltage()
{
    volatile int16_t result = 0;
    volatile float precise_result = 0;

    // Configure SAADC singled-ended channel, Internal reference (0.6V) and 1/6 gain.
    NRF_SAADC->CH[0].CONFIG = (SAADC_CH_CONFIG_GAIN_Gain1_6    << SAADC_CH_CONFIG_GAIN_Pos) |
                            (SAADC_CH_CONFIG_MODE_SE         << SAADC_CH_CONFIG_MODE_Pos) |
                            (SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos) |
                            (SAADC_CH_CONFIG_RESN_Bypass     << SAADC_CH_CONFIG_RESN_Pos) |
                            (SAADC_CH_CONFIG_RESP_Bypass     << SAADC_CH_CONFIG_RESP_Pos) |
                            (SAADC_CH_CONFIG_TACQ_3us        << SAADC_CH_CONFIG_TACQ_Pos);

    // Configure the SAADC channel with VDD as positive input, no negative input(single ended).
    NRF_SAADC->CH[0].PSELP = SAADC_CH_PSELP_PSELP_VDD << SAADC_CH_PSELP_PSELP_Pos;
    NRF_SAADC->CH[0].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;

    // Configure the SAADC resolution.
    NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_14bit << SAADC_RESOLUTION_VAL_Pos;

    // Configure result to be put in RAM at the location of "result" variable.
    NRF_SAADC->RESULT.MAXCNT = 1;
    NRF_SAADC->RESULT.PTR = (uint32_t)&result;

    // No automatic sampling, will trigger with TASKS_SAMPLE.
    NRF_SAADC->SAMPLERATE = SAADC_SAMPLERATE_MODE_Task << SAADC_SAMPLERATE_MODE_Pos;

    // Enable SAADC (would capture analog pins if they were used in CH[0].PSELP)
    NRF_SAADC->ENABLE = SAADC_ENABLE_ENABLE_Enabled << SAADC_ENABLE_ENABLE_Pos;

    // Calibrate the SAADC (only needs to be done once in a while)
    NRF_SAADC->TASKS_CALIBRATEOFFSET = 1;
    while (NRF_SAADC->EVENTS_CALIBRATEDONE == 0);
    NRF_SAADC->EVENTS_CALIBRATEDONE = 0;
    while (NRF_SAADC->STATUS == (SAADC_STATUS_STATUS_Busy <<SAADC_STATUS_STATUS_Pos));

    // Start the SAADC and wait for the started event.
    NRF_SAADC->TASKS_START = 1;
    while (NRF_SAADC->EVENTS_STARTED == 0);
    NRF_SAADC->EVENTS_STARTED = 0;

    // Do a SAADC sample, will put the result in the configured RAM buffer.
    NRF_SAADC->TASKS_SAMPLE = 1;
    while (NRF_SAADC->EVENTS_END == 0);
    NRF_SAADC->EVENTS_END = 0;

    // Convert the result to voltage
    // Result = [V(p) - V(n)] * GAIN/REFERENCE * 2^(RESOLUTION)
    // Result = (VDD - 0) * ((1/6) / 0.6) * 2^14
    // VDD = Result / 4551.1
    precise_result = (float)result / 4551.1f;

    // Stop the SAADC, since it's not used anymore.
    NRF_SAADC->TASKS_STOP = 1;
    while (NRF_SAADC->EVENTS_STOPPED == 0);
    NRF_SAADC->EVENTS_STOPPED = 0;

    return (uint16_t)(precise_result*1000);
}