N6 PLL: FRAC change on the fly as in H7 impossible ?

[LCE]

Heyho,

the title says it...

In RM0486, 14.6.5 PLL description, page 437 / 438 I find this:

Using the PLLs in fractional mode

PLL off ... set FRAC ... PLL on

Caution: Do not update DIVN and DIVNFRAC after the PLL has been enabled.

On the other hand, there are comments that some dividers can be changed on the fly.

So maybe it might work? Has anybody tried?

With these 4 PLLs and the great clock routing possibilities, the ability to change FRAC values on the fly with this high resolution would be a fantastic feature for synchronization, without using an external VCO.

[FBL · Accepted solution]

Hi @LCE 

For  STM32N6, you should not change the FRAC value on the fly. The PLL must be disabled before updating DIVN or DIVNFRAC, as per the official RM0486.

[LCE]

Thanks, would have been a great feature.