i need help.
We use nrf52840 and DK17.0.2
Using saadc with oversampling x8 , Single-ended mode.
Question
When Event monitoring using limits , Is the timing at which the conversion results are compared after averaging?
Or will it be compared for each sampling?
Processing to exclude when it is out of range even once before being averaged thinking about.
Best Regards,
take.
Hi,
The Limit event is not generated until after averaging (when END event is generated).
I just verified this using the following code (modified from https://github.com/andenore/NordicSnippets/blob/master/examples/saadc/main.c):
/**
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/** @file
* @defgroup nrf_adc_example main.c
* @{
* @ingroup nrf_adc_example
* @brief ADC Example Application main file.
*
* This file contains the source code for a sample application using ADC.
*
* @image html example_board_setup_a.jpg "Use board setup A for this example."
*/
#include <nrf.h>
int main(void)
{
volatile int16_t result = 0;
static int16_t sample_count = 0;
volatile float precise_result = 0;
// Start HFCLK from crystal oscillator, this will give the SAADC higher accuracy
NRF_CLOCK->TASKS_HFCLKSTART = 1;
while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
NRF_CLOCK->EVENTS_HFCLKSTARTED = 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_10us << 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_AnalogInput0 << SAADC_CH_PSELP_PSELP_Pos;
NRF_SAADC->CH[0].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;
NRF_SAADC->CH[0].LIMIT = (3000 << SAADC_CH_LIMIT_HIGH_Pos) | (500 << SAADC_CH_LIMIT_LOW_Pos);
// Configure the SAADC resolution.
NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_12bit << SAADC_RESOLUTION_VAL_Pos;
NRF_SAADC->OVERSAMPLE = SAADC_OVERSAMPLE_OVERSAMPLE_Over8x << SAADC_OVERSAMPLE_OVERSAMPLE_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;
NRF_SAADC->EVENTS_CH[0].LIMITH = 0;
NRF_SAADC->EVENTS_CH[0].LIMITL = 0;
NRF_SAADC->EVENTS_DONE = 0;
// Do a SAADC sample, will put the result in the configured RAM buffer.
while(NRF_SAADC->EVENTS_CH[0].LIMITH == 0 && NRF_SAADC->EVENTS_CH[0].LIMITL == 0)
{
NRF_SAADC->TASKS_SAMPLE = 1;
while(NRF_SAADC->EVENTS_DONE == 0);
sample_count++;
NRF_SAADC->EVENTS_DONE = 0;
}
while (NRF_SAADC->EVENTS_END == 0);
sample_count = sample_count;
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;
precise_result; // to get rid of set but not used warning
// 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;
while (1)
{
__WFE();
}
}
The sample_count variable is 8 after the LIMITH/LIMITL events is generated, if the input pin is connected to GND or VDD before running the application.
Best regards,
Jørgen
I'm sorry for the late reply.
I understand.
Thank you very much.