Kinetis MicrocontrollersのトピックClock Settings

Clock Settings

john71 — Wed, 28 Jun 2017 06:22:40 GMT

I have a project powered with a battery. So in order to reduce power consumption (besides sleep mode) I want to lower the clock frequency.

But in pll_init() I see the following limitations

// Check PLL divider settings are within spec.
if ((prdiv_val < 1) || (prdiv_val > 8)) {return 0x41;}
if ((vdiv_val < 16) || (vdiv_val > 47)) {return 0x42;}

// Check PLL reference clock frequency is within spec.
ref_freq = crystal_val / prdiv_val;
if ((ref_freq < 8000000) || (ref_freq > 32000000)) {return 0x43;}

// Check PLL output frequency is within spec.
pll_freq = (crystal_val / prdiv_val) * vdiv_val;
if ((pll_freq < 180000000) || (pll_freq > 360000000)) {return 0x45;}

The last limitation contradicts others. Or I don't understand something.

What minimum frequency I can get, considering I work with MK70FN1M0VMJ12?

Re: Clock Settings

Hui_Ma — Fri, 30 Jun 2017 06:33:17 GMT

Hi,

The K70 MCG module provides more working mode, the PEE is one working mode using PLL provide the system/core clock. The MCG module supports below working mode:

The K70 PLL output Min. clock frequency is 90MHz:

Customer could consider to use MCG working with FBE mode, which is using external oscillator clock as system/core clock .

Wish it helps.

Have a great day,
Ma Hui

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Re: Clock Settings

john71 — Sat, 01 Jul 2017 14:08:07 GMT

I see. Thank you.