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LSERDY is asserted even if oscillator is not connected

load2005
Associate III

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?

6 REPLIES 6

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

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

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load2005
Associate III

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

Uwe Bonnes
Principal III

Better disable RCC_BCDR_LSEON and keep the LSE pins floating.

load2005
Associate III

Hi all

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

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