KE18 auto trim frequency

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KE18 auto trim frequency

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davidsherman
Senior Contributor I

The KE18F512 manual mentions trimming the FIRC clock, and shows registers for enabling the auto trim from an external clock.  It shows the divider settings as well, but the one thing it doesn't mention is what the reference frequency is supposed to be.  What is the reference frequency?

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davidsherman
Senior Contributor I

Still looking for an answer on this, the reference manual is lacking some information, like what frequency the auto tune expects to use the auto tune feature.  Can this feature be used?

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Robin_Shen
NXP TechSupport
NXP TechSupport

Hi David,

Sorry for the inconvenience.

I have asked the Kinetis AE team for help on this case. And I will inform you as soon as I get any feedback.

 

Best Regards,

Robin

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davidsherman
Senior Contributor I

Thank you for looking into this, I appreciate it.

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Robin_Shen
NXP TechSupport
NXP TechSupport

The Fast IRC Trim Predivide[TRIMDIV] is intended for the SOSC and the expectation is to set the div ratio to give you a 31250Hz divided clock, so it configure the SCG_FIRCTCFG[TRIMDIV] according the external OSC frequency.

Best Regards,

Robin

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Robin_Shen
NXP TechSupport
NXP TechSupport

Hi David,

Sorry for the late reply!

System OSC can be configured as clock source to tune the Fast IRC.

SCG_FIRCTCFG.png

Figure 18-1. Clocking Diagram.png

And you can find the frequency in  'Table 44. External Oscillator frequency specifications (OSC)' of KE1xFP100M168SF0.

Table 44. External Oscillator frequency specifications (OSC).png

Best Regards,

Robin

 

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davidsherman
Senior Contributor I

Unfortunately, that didn't answer my question at all.  I've already seen exactly what you've posted, there is no mention of the reference frequency the auto tune needs.  It talks about the divider "divide the system OSC down for Fast IRC trimming", but what frequency do you divide it down to?  The frequency ranges you mention only show the ranges the oscillator is capable of working, not what the reference frequency for fast IRC trimming is.

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