STM32H7 Internal RTC Accuracy

[ttemc.1]

Dear Team,

Could you please provide the internal RTC accuracy for the STM32H7 microcontroller?

Additionally, I clarify the following point: 'Digital calibration circuit with 0.95 ppm resolution, to compensate for quartz crystal inaccuracy.

 

Regards,

TEMC - Efftronics systems Pvt Ltd

[AScha.3]

Hi,

There is no internal RTC, so no accuracy value.

There is a internal LSI, RC oscillator, that can be used for some raw timing, but not for any good RTC.

You have to add an external crystal, LSE, set the drive level high, add the load caps matching the crystals datasheet.

[ttemc.1]

Dear A Scha,

This means the accuracy of the RTC depends entirely on the external crystal, right? Regarding my previous post about the 'digital calibration circuit with 0.95 ppm resolution to compensate for quartz crystal inaccuracy,' could you please clarify that specific point?

 

Regards,

TEMC - Efftronics systems Pvt Ltd

[Andrew Neil]

This means the accuracy of the RTC depends entirely on the external crystal, right

Of course: the accuracy of any clock - whether electric, electronic, mechanical, or whatever - depends entirely on its timing reference.

[Gyessine]

Hello ​@ttemc.1 

RTC can use LSI as clock source, which is a 32 kHz clock.

But for the best accuracy, LSE is better as clock source for the RTC. The LSE clock frequency is 32 768 Hz.

If the application must use LSI, you can maximize accuracy by modifying the asynchronous and synchronous prescaler registers and by applying smooth calibration. The following article explains how to do this.
BR
Gyessine

[Andrew Neil]

the STM32H7 microcontroller

Which one ?

“STM32H7” is a whole family of microcontrollers:

https://www.st.com/en/microcontrollers-microprocessors/stm32h7-series.html

Please give your specific part number.

 

clarify the following point: 'Digital calibration circuit with 0.95 ppm resolution, to compensate for quartz crystal inaccuracy.

Where, exactly, did you find that point?

 

 

 

[ttemc.1]

Dear Andrew Neil,

 

In STM32H755xI part we find that line. 

Regards,

TEMC - Efftronics systems Pvt Ltd

[Andrew Neil]

So that’s the “overview” - read on to find the detailed description …

You may need to see the Reference Manuals RM0399, STM32H745/755 and STM32H747/757 advanced Arm®-based 32-bit MCUs:

https://www.st.com/resource/en/reference_manual/rm0399-stm32h745755-and-stm32h747757-advanced-armbased-32bit-mcus-stmicroelectronics.pdf

 

See also Application Notes AN4759, Introduction to using the hardware real-time clock (RTC) and the tamper management unit (TAMP) for STM32 MCUs:

https://www.st.com/resource/en/application_note/an4759-introduction-to-using-the-hardware-realtime-clock-rtc-and-the-tamper-management-unit-tamp-for-stm32-mcus-stmicroelectronics.pdf

 

via: https://www.st.com/en/microcontrollers-microprocessors/stm32h755xi.html#documentation