Fractional mode register changes need a delay?

[AlbertoGarlassi]

I'm trying to change the PLLxFRACR on-the fly. Per the reference manual something like this should work:

__HAL_RCC_PLL2FRACN_DISABLE();

__HAL_RCC_PLL2FRACN_CONFIG(8191);

__HAL_RCC_PLL2FRACN_ENABLE();

On a STM32H750 this code seems to have no effect. But works OK wihen a delay between the disable and the config lines is inserted. Some microseconds is enough.

Is it really this way or am I missing something?

Regards

Alberto

[AlbertoGarlassi]

Ok, it makes sense, thanks. Only thing I can add is that it seems that the delay needed is not fixed, sometimes the register is updated even without any delay. So we need a worst-case value.

[KDJEM.1]

Hello @Piranha ,

The RCC_PLL3FRACR register bit field typo is fixed in RM0433 Rev 8.

Thank you.

Kaouthar