How to set PDM_CLK properly, when it is lower than default?

[Kirill_K]

Hi!
I ran into a little misunderstanding in setting up clock frequency for PDM. I need to work with lower clock frequency than default - 0.64 MHz. I see, that PDM_CLK = 32/Prescaler, and Prescaler correlates with the content of PDMCLKCTRL register. It seems, that change PDMCLKCTRL by 0x00400000 changes Prescaler by 1. Assuming that, I found necessary values of Prescaler and PDMCLKCTRL (PDMCLKCTRL = 0x03800000, Prescaler = 50). But tests showed that with these settings real PDM_CLK is lower than expected, about 0.45 MHz.
My question is: how to correlate PDMCLKCTRL and Prescaler value? Is there some equation for that?

[Sigurd]

Hi,

There is not a simple equation for this. You could try PDMCLKCTRL 0x05100000 in order to get 0.64 MHz

Note that only the values listed in the PS have been fully and thoroughly tested. If you are using values that are not listed in the PS, we cannot guarantee that they will work and it will be on your own risk.

[Kirill_K]

Ok, thank you