RTC hrtc.Init.AsynchPrediv & hrtc.Init.SynchPrediv = 10 Registers

[erastusC]

Can somebody please help me.

The code below is initializing the RTC.

The clock works I can set and read time and date no problem.

Somehow if I change these register:

hrtc.Init.AsynchPrediv = 131;

hrtc.Init.SynchPrediv = 10;

It has no impact on the clock accuracy I keep on gaining time.

I would have thought by "tweaking" the values it will either speed up or slow down the RTC.

 Code was generated by using the STM32 cube IDE.

/** Initialize RTC */

hrtc.Instance = RTC;

hrtc.Init.HourFormat = RTC_HOURFORMAT_24;

hrtc.Init.AsynchPrediv = 131;

hrtc.Init.SynchPrediv = 10;

hrtc.Init.OutPut = RTC_OUTPUT_DISABLE;

hrtc.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;

hrtc.Init.OutPutType = RTC_OUTPUT_TYPE_OPENDRAIN;

if (HAL_RTC_Init(&hrtc) != HAL_OK)

{

Error_Handler();

}



/* USER CODE BEGIN Check_RTC_BKUP */



/* USER CODE END Check_RTC_BKUP */



/** Initialize RTC and set the Time and Date

*/

sTime.Hours = 13;

sTime.Minutes = 58;

sTime.Seconds = 0;

sTime.DayLightSaving = RTC_DAYLIGHTSAVING_NONE;

sTime.StoreOperation = RTC_STOREOPERATION_RESET;

if (HAL_RTC_SetTime(&hrtc, &sTime, RTC_FORMAT_BIN) != HAL_OK)

{

Error_Handler();

}

sDate.WeekDay = RTC_WEEKDAY_WEDNESDAY;

sDate.Month = RTC_MONTH_NOVEMBER;

sDate.Date = 19;

sDate.Year = 25;



if (HAL_RTC_SetDate(&hrtc, &sDate, RTC_FORMAT_BIN) != HAL_OK)

{

Error_Handler();

}

[Gyessine · Accepted solution]

hello @erastusC 
Based on AN4759, RTC prescalers are used to adjust power consumption. Tweaking them can reduce power consumption. The RTC is programmed to provide a precise time-of-day clock.
BR
Gyessine

[erastusC]

Many thanks I did not understand it properly.

Thanks

[waclawek.jan]

Somehow if I change these register:

hrtc.Init.AsynchPrediv = 131;

hrtc.Init.SynchPrediv = 10;

It has no impact on the clock accuracy I keep on gaining time.

How do you know this has no impact on clock accuracy?

JW