LSERDY is asserted even if oscillator is not connected

[load2005]

I am using stm32F746. I have enabled the RTC via external oscillator using CubeMX.

The crystal is not connected. But I see that RTC is initialized without errors (no timeout) and LSERDY is 1. Manual says LSERDY is 1 when external oscillator is running.

How that could be possible?

[waclawek.jan]

Is the oscillator input pin of floating? It may pick up noise.

The LSERDY circuit is a counter, there's no discrimination for the frequency.

JW

[Tesla DeLorean]

That's kind of weird, a custom design? Things hung of PC13..15 ?

[load2005]

Thanks for reply. They are floating. I will try to ground them and check.

[Uwe Bonnes]

Better disable RCC_BCDR_LSEON and keep the LSE pins floating.

[load2005]

Hi all

I have checked that if both pins of oscillator are connected to the ground LSERDY is still set. A bit strange.

[waclawek.jan]

That indeed is.

Can you please output LSE to MCO1 and check if there are no oscillations?

You don't set LSEBYP, do you?

JW