RTC time is not kept in Stm32f103 by vbat

Question

I am using stm32f103c8 and External Clock Crystal (LSE). I connected the Vbat with a 1220 coin battery. But when I turn off VDD and turn on the micro again, the time and date are all zero. Why time is reset? Do I have to change the code too?

static void MX_RTC_Init(void)
{
RTC_TimeTypeDef sTime = {0};
RTC_DateTypeDef DateToUpdate = {0};
hrtc.Instance = RTC;
hrtc.Init.AsynchPrediv = RTC_AUTO_1_SECOND;
hrtc.Init.OutPut = RTC_OUTPUTSOURCE_ALARM;
if (HAL_RTC_Init(&hrtc) != HAL_OK)
{
 Error_Handler();
}
if (HAL_RTC_SetTime(&hrtc, &sTime, RTC_FORMAT_BIN) != HAL_OK)
{
 Error_Handler();
}
 if (HAL_RTC_SetDate(&hrtc, &DateToUpdate, RTC_FORMAT_BIN) != HAL_OK)
 {
 Error_Handler();
 }
}

I set the RTC time with interrupt.

• Colin: Do you run that code every time the processor boots? It looks like that sets the date and time...
• brhans: What do you think happens when you execute HAL_RTC_SetTime(...) and HAL_RTC_SetDate(...) with both sTime and DateToUpdate both set to all zeroes?
• Mojtaba Miraki: So what should I write here?
• brhans: You haven't answered my question.

Answer 1

That code sets time and date every time it is run. You obviously need to change it so that time and date is not set if it is already set and backed up by the battery.

• Mojtaba Miraki: Can you tell me exactly where should be changed please?
• Justme: You better look at STM32 RTC examples and API documentation.
• Mojtaba Miraki: So if you know, tell me what should I do? I am confused.
• Justme: I have never used the battery backup so I would have to figure it out myself too. You asked why the time is reset and if you have to change code, and those questions were easy to answer. Did you look at ST code examples and API documentation?