rtc clock source

[newherogg-netizen]

Most of MCUs may have rtc as integrated which may has clock source options such as ext xtal, int. rc osc, or pll on mcu clock.
Which one is used for micropython as default? Guessing as PLL MCU Clock, it may differ from MCU to MCU. Actually I'm focusing on ESP32 C3 supermini board which does have ext xtal for RTC.

I could find many micropython projects on internet sites which have seperated RTC modules such as PCF85063A. I just wonder if the cheaper RTC modules with ext Xtal have better accuracy than internal RTCs of the MCUs.

[Josverl]

I think you are asking : Why ?
External sub-boards such as the PCF85063A will keep time wile the MCU is sleeping , or off.
It may even act as a wake source.

I would expect a specialized clock board to have better accuracy , and support for leap-years DST etc , but if it is really cheap - then the accuracy may not be up to par.
periodic SNTP may help - but it really depends on your use case.
https://github.com/ekondayan/micropython-ntp

[newherogg-netizen]

Thank you for your comments.
Oh, I couldn't consider the battery backup feature.

[peterhinch]

I just wonder if the cheaper RTC modules with ext Xtal have better accuracy than internal RTCs of the MCUs.

Depends on the MCU. ESP8266 has a lousy RTC, for example. An external RTC such as DS3231 or MAX31328 will have an accuracy of about 2mins/yr, which is better than an uncalibrated MCU crystal oscillator. However some MCU's (STM for example) allow the oscillator to be calibrated to similar accuracy (given a reference time source). An external RTC will have battery backup - but some MCU's also support this.

So there's no general answer.

[newherogg-netizen]

Thank you for your comments.
I've used DS3231 module before for my small projects, expecting just better accuracy besides other features.
But it was not satisfactory. Later I guessed that the cheaper chinese module used fake chip, maybe.

[peterhinch]

Later I guessed that the cheaper chinese module used fake chip, maybe.

Very possibly. Real DS3231modules are extremely accurate (as per their spec).