I have been trying to implement calendar functionality on my STM32f103C8 using the built in RTC peripheral.
Going through the RTC section of the reference manual, it states that the clock source to RTC can be either of HSE/128 or LSE or LSI. So far so good.
But then I found this regarding RTC in the RCC section
What do they mean by "RTC state is not guranteed if the Vdd supply is powered off..." when using HSE/128 as the RTC clock source? I was under the impression that as long as the BACKUP domain is not resetted (Vbat present if Vdd turned off), the RTC state would be maintained. Isn't that the whole point of RTC?