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How to keep HSI running in STOP mode?

Associate II

Hello support team.

I'm using the STM32L011D4P, I configured the MCO output to repeat the HSI oscillator output divided by 16 and have a 1 MHz signal. With the help of an oscilloscope it is possible to identify a 1 MHz square wave.

In the datasheet, I discovered that it is possible to keep the HSI active even in STOP mode, activating the HSI16KERON bit in the RCC_CR register. I am using the LL_RCC_HSI_EnableInStopMode() function to activate HSI16KERON.

To enter low power mode, I am calling the function: HAL_PWR_EnterSTOPMode (PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI), but the 1 MHz signal from the MCO pin disappears.

In STOP mode is the HSI oscillator being turned off, or is only the MCO pin output being turned off?

I would like the 1 MHz signal to remain working during the low power phase (STOP).

Best Regards.

ST Employee

Hello @Takahashi ,


By default on STM32L0 devices all clocks are turned off in Stop mode but the HSI16 can run when HSI16KERON is set, as you did by calling the function LL_RCC_HSI_EnableInStopMode(). 

But the MCO is not available in Stop mode that is why the output disappears, on other products like the STM32U5 for instance we have the LSCO (Low-speed output clock) why remains available in low power modes. Unfortunately this feature is not on STM32L0 devices.


Best regards,


Associate II

Thank you very much for the answer Aime.

Would it be possible to use some other low consumption mode to achieve this goal?
If so, what would that mode be and what is the estimated consumption?


Best Regards.

Hi @Aime ,

> But the MCO is not available in Stop mode

Where is this documented?