Clock source used by SAADC and UART ?

RE: Clock source used by SAADC and UART ?

John — Tue, 28 Mar 2023 13:35:23 GMT

Hi haakonsh Where in the datasheet is this mentioned that all peripherals runs on PCLK16M? Is there any peripherals that run on other clock sources like PCLK1M and PCLK32?

RE: Clock source used by SAADC and UART ?

haakonsh — Wed, 25 Mar 2020 13:42:59 GMT

All peripherals run on PCLK16M unless otherwise stated, that's why it's advisable to run HFXO for best results.

RE: Clock source used by SAADC and UART ?

Nathan O. — Wed, 25 Mar 2020 13:00:14 GMT

The sample() function is already called periodically through the use of the app_timer module in my code.

I was actually wondering what clock was used to handle the acquisition time and to make the SAADC actualy work (for a single sample).

RE: Clock source used by SAADC and UART ?

haakonsh — Wed, 25 Mar 2020 11:54:01 GMT

No, you're just manually triggering the SAMPLE TASK from CPU once by calling nrf_drv_saadc_sample().

You need to set-up a TIMER with a COMPARE EVENT connected to the SAADC's SAMPLE TASK to continuously trigger sample the SAADC.

Remember to set an acquisition time relative to your source impedance, according to the SAADC spec. See the Acquisition time chapter for details.

RE: Clock source used by SAADC and UART ?

Nathan O. — Wed, 25 Mar 2020 11:00:03 GMT

Thanks for your answers.

Regarding the point 3, this is what I use to configure and start the SAADC :

  static const nrf_drv_saadc_config_t config = {
    .resolution = NRF_SAADC_RESOLUTION_12BIT,
    .oversample = NRF_SAADC_OVERSAMPLE_DISABLED,
    .interrupt_priority = APP_SAADC_IRQ_PRIORITY,
    .low_power_mode = false,
  };
  
  ...
  
  nrf_saadc_channel_config_t channel_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(SAADC_INPUT_BATT);
  err_code = nrf_drv_saadc_channel_init(SAADC_CHANNEL_BATT, &channel_config);
  
  ...
  
  nrf_drv_saadc_sample();

I guess it's TIMER with PCLK26M that's used in this case by the SAADC (for sampling I mean not for triggering the conversion) ?

RE: Clock source used by SAADC and UART ?

haakonsh — Wed, 25 Mar 2020 10:50:35 GMT

Yes, you are correct.
I believe it's PCLK16M. Both PCLK16M and 1M are just clock divisions from HFCLK.
The RTC uses the LFCLK, the TIMER uses PCLK16M. Any EVENT from any peripheral can be used to trigger the SAADC's SAMPLE TASK, not just the timers/counters. For best SAADC results it's recommended to use the TIMER with HFXO running.
Yup!