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Clocking the MK20FX512 with Processor Expert?

Question asked by Simon Haines on Jan 12, 2016
Latest reply on Jan 25, 2016 by Simon Haines

I'm trying to clock a Kinetis MK20FX512 at 96MHz core clock speed and 48MHz bus speed with Processor Expert. I have a 32.768kHz crystal attached to XTAL32/EXTAL32 (with nothing on XTAL0/EXTAL0 and XTAL1/EXTAL1) and I am able to set the following configuration manually in code:

  • RTC OSCE 32.768 kHz oscillator is enabled
  • SIM OSC32KSEL RTC oscillator selected as 32kHz clock source (ERCLK32K)
  • SIM PLLFLLSEL MCGFLLCLK selected for various peripheral clocking options
  • SIM OUTDIV1 Sys: /1
  • SIM OUTDIV2 Bus: /2
  • OSC0 ERCLKEN External reference clock enabled
  • OSC1 ERCLKEN External reference clock enabled
  • MCG OSCSEL 32kHz RTC oscillator selected as FLL external reference clock
  • MCG RANGE0 Low frequency range selected for crystal oscillator
  • MCG HGO0 High gain oscillator configured for low-power operation
  • MCG EREFS0 External reference clock selected (not oscillator) as EREF source
  • MCG IRCS Slow internal reference clock selected (instead of fast IREF)
  • MCG CLKS Output of FLL selected as clock source
  • MCG FRDIV /1 divider for external reference clock (OSCSEL has reset value of 0)
  • MCG IREFS External reference clock selected as source for the FLL
  • MCG IRCLKEN Internal reference clock is enabled
  • MCG IREFSTEN Internal reference clock is disabled in stop mode
  • MCG DMX32 DRST_DRS DCO range is 96MHz


This produces the desired core clock speed of 96MHz and bus speed of 48MHz. Using processor expert, I can't select XTAL32/EXTAL32 as the clock source for the RTC (only RTC_CLKIN is available) or the DMX32 and DRST_DRS values to get the clock to 96MHz. The highest value seems to be 47.972352MHz. Is this a problem with my configuration or with Processor Expert?