Interfacing PDM digital microphones using STM32 MCUs and MPUs

[AShpi.2]

Hi,

At Application Note 5027: "Interfacing PDM digital microphones using STM32 MCUs and MPUs" it described how to connect PDM microphone to SPI I/F of STM32. My question is:

at SPI I/F clock is active only when there is SPI transaction, how can I cause the SPI clock to be active constantly?

Thanks

Aaharon

[SimonePradolini]

Hi @AShpi.2​ ,

Chapter 2.1 explains the SPI use case: SPI is set as master only (so MOSI is not used), L/R (that is the CS) is set HIGH or LOW and data can be read consequently on MISO pin on falling or rising edge of the clock.

Once you feed a proper clock to the ST MEMS microphones, it starts generating data. It is always on, no data ready or other signal must be interpreted.

So, by just setting the SPI as explained above, the mic receives the clock and starts emitting PDM signal on MISO, CS is always active and so SPI will continuously remain active.

Best regards

Simone