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load2005
load2005
Associate III
August 1, 2019
Question

LSERDY is asserted even if oscillator is not connected

  • August 1, 2019
  • 6 replies
  • 1096 views

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?

This topic has been closed for replies.

6 replies

waclawek.jan
waclawek.jan
Super User
August 1, 2019

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
Tesla DeLorean
Guru
August 1, 2019

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

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load2005
load2005Author
Associate III
August 1, 2019

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

Uwe Bonnes
Uwe Bonnes
Chief
August 1, 2019

Better disable RCC_BCDR_LSEON and keep the LSE pins floating.

load2005
load2005Author
Associate III
August 11, 2019

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
waclawek.jan
Super User
August 12, 2019

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

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