Clock using internal 48M-IRC oscillator

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Clock using internal 48M-IRC oscillator

Contributor II

Hello all, 

We are working on K24 and we are switching from 8MHz crystal to the IRC48M internal oscillator for our legacy systems.

We have observed that the controller operates in FEI mode on RESET and moves into PEE mode. 

It transitions from FEI -> FBE -> PBE -> PEE mode.

While we are able to generate the same core, bus and flash frequencies in FEI and PEE mode, we are unable to generate similar frequency(generating higher frequency) as the legacy system in FBE and PBE mode using OUTDIV. 

My question is, since we are entering FBE and PBE only to transition to PEE is it okay to have higher frequencies than the legacy systems?


Please find the table to see the frequencies: 

Modes8MHz crystal output48MIRC oscillator output
FBE and PBE modes

8 MHz - Core

4 MHz - Bus

1.6MHz - Flash

1.6Mhz - Flex

48 MHz - Core

24 MHz - Bus

9.6 MHz - Flash

9.6MHz - Flash

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Specialist V

Hi Sachin

As long as the clocks are within specification during the transition there is no problem.

See for practical MCG guide.


[uTasker project developer for Kinetis and i.MX RT]