STM32F030 Datasheet here.
- On page 14, it's mentioned that:
"System clock selection is performed on startup, however the internal RC 8 MHz oscillator is selected as default CPU clock on reset. An external 4-32 MHz clock can be selected, in which case it is monitored for failure."
I believe that microcontroller can be run perfectly using internal crystal. Am I right? If I am, then in what cases would someone want to connect an external crystal to the controller? Is it to run the controller at a lower frequency (to save power)? I think this can also be achieved by setting some prescalers on the internal clock. Are there certain applications which mandate the requirement of an external crystal? If yes, what could they be?
- Page 21 says:
The RTC clock sources can be:
• A 32.768 kHz external crystal
• A resonator or oscillator
• The internal low-power RC oscillator (typical frequency of 40 kHz)
• The high-speed external clock divided by 32
Will RTC be able to keep accurate time on internal clock source? I am fine with +-5 seconds per day. Can I achieve that comfortably?
I have always seen 32.768 kHz crystal being used with RTC chips which makes it easy to count due to 2^15 value. However internal clock source gives it a 40 kHz signal. Could there be any issues arising due to this?
- Usually in microcontrollers with internal RTC, there is a dedicated VBAT pin which is used to keep the RTC alive during power failure. I couldn't find such a pin on this device. Where can I connect the battery to get the intended backup supply for RTC? There are multiple VDD pins but I am unable to make out whether one of them is VBAT pin or not and if yes, then which one. Pin definitions are from page 28-33.