NRF52840 SPI Clock configuration

RE: NRF52840 SPI Clock configuration

Jørgen Holmefjord — Thu, 25 Oct 2018 14:59:28 GMT

Hi,

Even if it is possible to set other values in the frequency register, it is not recommended to use other values than the ones specified in the product specifications.

Other values are not tested, and using them can cause unexpected behavior.

Best regards,
Jørgen

RE: NRF52840 SPI Clock configuration

lemi — Thu, 25 Oct 2018 13:55:10 GMT

Thank you for your fast reply.

Is there a documentation or schematic how exactly this divider is working? Because i've seen the divider uses Bit number 31 to 19, therefore I am able to decrease the speed to 2000Hz (which i've measured). I did not find any information inside the product specification of the NRF52840

Is it possible to change the peripherial clock (use PCLK32 instead) ?

RE: NRF52840 SPI Clock configuration

Turbo J — Thu, 25 Oct 2018 13:41:04 GMT

Your <=10kHz SPI clock won't be possible in hardware. The Frequency divider is based on the 64 (SPIM3) or 16MHz peripherial clock and has a limited number of dividing "bits" - 125kHz is the slowest available speed.

Below that you either need bit-bangig (manually toggeling GPIOs in software) or you could try to use a PWM peripherial in case you don't need MISO data.