NRF52840 PDM Clock Control Value for Stereo Application

[joer55]

Hi:

I am working on a stereo microphone application using the NRF52840.  I would like to have the 2 microphones output 16K samples per second (8K samples each for left and right microphones). I can set the PDMCLKCTRL register for 32K samples per second (16K samples per microphone, using PDMCLKCTRL value 0x0A00 0000) but cannot find any reference for setting it to a lower value.

I found a formula for the NRF53x PDM for setting the PDMCLKCTRL but it does not seem to apply to the NRF52x  (PDMCLKCTRL = 4096 * [(Fpdm * 1048576) / (Fsrc + (Fpdm/2))] ) .

Could I get the formula for setting the PDMCLKCTRL register (or a value for 8K per channel output)?  Either divisor (64 or 80) value would be fine.

Thanks,

Joe

[Jørgen Holmefjord]

Hi,

Please have a look at this post. I assume half the frequency (0x0A00 0000 = 1.280 MHz --> /2 = 0.64 MHz) should be correct for what you want to achieve?

Note that other configurations than the ones listed in the PS is not tested/verified and may not function correctly.

Best regards,
Jørgen

[joer55]

Hi Jorgen:

Thanks for the reply, yes, the value from that post looks to be correct.  I do understand that non-PS listed values may not work correctly.

Best Regards,

Joe