nrf52832 Peripheral Clock Assignment

[ptskyin]

Hi,

The nrf52832 product spec shows all the clocks provided by HFCLK and LFCLK. But where can I find which peripheral is using which peripheral clock specifically?

For example, which clock is used by UART and TWI?

Thanks for the help in advance!

[Dmitry]

Hi,

LFCLK is used by RTC and WDT, maybe also LPCOMP (if it needs any clock at all). Others use HFCLK.

[nothingmuchyou]

This doesn't really answer the original question. Where in the product specification does it say where each clock goes?? I've been looking for awhile. 

[Dmitry]

Yes, there is no such info in a single place for quick look, only in description of modules that use clock different from PCLK16. LFCLK is mentioned in spec for RTC and WDT, the same is for radio and NFC that require HFXO. Other modules will use either HFINT running on-demand, or HFXO if it's already started. Most are running from PCLK16M, timers can work from PCLK1M when it's sufficient, PCLK32M is used for I2S and PDM. Anyway you can't control these lines independently.

What's really missing is a notice about switching between HFINT and HFXO - while it looks quite clear, many developers are got catched. Because of a difference in frequency, this switching sometimes causes issues especially with UART and PWM.

[nothingmuchyou]

Dmitry said:

PCLK32M is used for I2S and PDM. Anyway you can't control these lines independently.

Could you point me to the place in the product specification that says this?

Dmitry said:

Most are running from PCLK16M

Could you also point me to the place in the product specification that says this?

[Dmitry]

nothingmuchyou said:

PCLK32M is used for I2S and PDM. Anyway you can't control these lines independently.

Could you point me to the place in the product specification that says this?

nRF52832 PS 1.4, pages 441 and 456 (master clock registers)

nothingmuchyou said:

Most are running from PCLK16M

Could you also point me to the place in the product specification that says this?

Unfortunately no, but it was mentioned by Nordic engineers many times on this forum, for example here.

[nothingmuchyou]

Thanks for your help Dmitry. Maybe this next question is silly but how do I know who is a Nordic engineer on this forum vs just a customer like me? It's hard to tell what to take as a spec in the datasheet vs what to take with a grain of salt.

[Sigurd]

Hi,

nothingmuchyou said:

how do I know who is a Nordic engineer on this forum vs just a customer like me?

If you hover your mouse cursor over the username picture/avatar, or click on the username, then Nordic engineers will have this kind of badge:

nothingmuchyou said:

Where in the product specification does it say where each clock goes??

There is no single table for this in the nRF52 PS, in the nRF51 PS we have this table:

ideally something similar should have been present in the nRF52 PS as well.

[nothingmuchyou]

Sigurd said:

ideally something similar should have been present in the nRF52 PS as well

Do you think there will be an update to the documentation?