AnsweredAssumed Answered


Question asked by John Russell on May 7, 2015
Latest reply on May 11, 2015 by John Russell



I'm currently migrating products from MC13224V to Kinetis Kw21D256 processors, using the TWR as a starting point, no problems there.

Have designed new boards for the actual product and have a problem with the 32MHz modem oscillator.

In document and in the kw Reference Manual MKW2xDxxxRM.pdf it is mentioned that the MC1324 modem has a feature that allows using trim caps internal to the silicon that allow the 32MHz crystal oscillator to be software trimmed.

For example in the reference manual :

"As described in “Crystal Trim Operation”, the modem crystal oscillator frequency can be

trimmed by programming modem XTAL_TRIM register. The trimming procedure varies

the frequency by a few hertz per step, depending on the type of crystal. As the


XTAL_TRIM register value is increased, the frequency is decreased. This feature is

useful for factory calibration of the crystal frequency to set the accuracy for the radio as

required by the 802.15.4 Standard."


However there is no XTAL_TRIM register mentioned in the modem registers section and no Crystal Trim Operation" section. I've checked all the direct and indirect register docs - nothing there.


Does the Mkw21D256 modem have the crystal trim feature mentioned in the docs?

If so, how is it accessed?