Not expected frequency on NUCLEO-L496 RTC output calibration

[Sirac]

Hi,

I'm trying to improve the accuracy of RTC. For that, I use the AN2604 witch describe this.

But, when I activate the calibration output of RTC at 512Hz, I have only 496Hz at the output. (AsynchPrediv =127). I tried this simple code to the nucleo-L476 and I have a perfect 512Hz clock.

On the L496, if I change AsynchPrediv to 124 and I can see a frequency around 512Hz.

What could be wrong with the L496?

[Sirac]

I change the board of L496 and again, same frequency. So I change the crystal, the frequency is slightly better (504Hz) but too far from 512Hz.

I hope there is no trouble with MCU itself

[waclawek.jan]

Try an external oscillator with LSE, e.g. a signal generator (setting LSEBYP, see External source (LSE bypass) subchapter in RM).

JW

[Sirac]

Good Idea, I test that asap

Thank's

[mbarg.1]

I have similar issue with Nucleo-H723G boards - i have 4 of them - LSE is runnig around 30800 Hz

[AScha.3]

try:

1. set LSE drive to high

2. make the caps on crystal smaller...what C-load your crystal should have?

[mbarg.1]

I have the problem on Nucleo-H723G boards with default (cubeIde 13.1) setup.

We use official demo boards with official demo sw to avoid discussions on hw/sw.

[waclawek.jan]

Please don't hijack threads.

Start your own thread stating the problem, what hw and what sw exactly (what is official demo sw?) did you use and how exactly do you detect the problem.

JW

[mbarg.1]

Sorry for mixing apples with potatoes...

I will open a new topic asap.