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STM32L0x1 Accurate LSE Clocks

Question asked by dobyns.marcie on Oct 21, 2015
Latest reply on Oct 21, 2015 by dobyns.marcie
Hello!

We are trying to generate a clock signal around 1.024MHz.  We currently have a 32768 watch crystal connected up and are hoping to get at least the 0.5% accuracy as alluded to in the reference guide:

Multispeed internal RC oscillator (MSI), trimmable by software, able to generate 7 frequencies (65 kHz, 131 kHz, 262 kHz, 524 kHz, 1.05 MHz, 2.1 MHz, 4.2 MHz). When a 32.768 kHz clock source is available in the system (LSE), the MSI frequency can be trimmed by software down to a ±0.5% accuracy

However, we're currently seeing quite a lot of jitter on the 32kHz signal, even when it's routed directly out to TP1.  If we need to switch to a 32kHz crystal we can, we just need to understand where all the jitter is coming from.

Is there any 'gotcha' setting we need to look into in order to use the crystal to trim the frequency better?  Is it because we're trying to get to 1.024MHz with the watch crystal instead of the x16 value of 1.048MHz?

Thanks!

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