Using TCXO with STM32L0

[JR2963]

Hello,

I would like to use TCXO (25 MHz) for timing STM32L071. It doesn't really work for me. When I put a scope probe behind C1, a signal can be seen in the picture. (some 27 Hz). Do you know what's wrong? The power supply for TCXO is 3.3

Please any idea? Thank you.

[Michal Dudka · Accepted solution]

Check if you are not looking at "aliasing"
https://www.tek.com/en/support/faqs/what-aliasing-and-how-do-i-detect-it-and-fix-it-my-oscilloscope

[JR2963]

HEY you are right!!  That's surprising! I'm currently observing a 25 MHz signal with about 2 Vpp between C and R.

Just can not see MCO outpu on PA8... Set in CubeMx..

[Michal Dudka]

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@JR2963 wrote:

Just can not see MCO outpu on PA8... Set in CubeMx..

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Read user manual to CubeMX (if exists), or set MCO by yourself without CubeMX... In LL API on STM32F0 it takes about three or four lines:

LL_AHB1_GRP1_EnableClock(LL_AHB1_GRP1_PERIPH_GPIOA); // Enable GPIOA clodk
LL_GPIO_SetPinMode(GPIOA,LL_GPIO_PIN_8,LL_GPIO_MODE_ALTERNATE); // Set PA8 to "alternate"
LL_GPIO_SetAFPin_8_15(GPIOA,LL_GPIO_PIN_8,LL_GPIO_AF_0); // select appropriate alternate function
LL_RCC_ConfigMCO(LL_RCC_MCO1SOURCE_SYSCLK,LL_RCC_MCO1_DIV_1); // select MCO source

By the way, what is purpose of C1 and R14 and how do you control DC voltage at PH0 input ?

[JR2963]

Now the MCO output works. Thank you!

So you think C1 and R14 are not necessary and I can connect it directly? (I came from some STM32 wiring where I saw C and R.)

[Michal Dudka]

More than unnecessary. I think that its wrong.