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STM32F4 external oscillator

Question asked by Gregorsanec.Toni on Jan 28, 2014
Latest reply on Jan 28, 2014 by Gregorsanec.Toni

I have connected external clock source of 25 MHz from local oscillator to the
OSC_IN pin of STM32F4. The problem is, that sometimes happens, that
CPU does not start from external HSE and bit RCC_CR_HSERDY is never set.
I checked clock with oscilloscope and it looks fine. I also put CPU in reset and
wait until oscillator stable, but even this does not guarantee valid start-up. 
In manual I did not found any detailed explanation about HSERDY bit when
CPU is clocked by the external clock source.

Is there any limitation when connection external oscillator instead of crystal?