FRDM-K66F, MCG and 12MHz.

[workalot]

Workalot is studyiing the MK66 MCU using the FRDM-K66F board and is seeking advice on MCG and 12MHz.

Is it so that 12MHz excludes use of the PLL as an 180MHz MCU clock? 16MHz would do it it seems.

[workalot]

Thank you Mark Butcher,

This and your advice at "MK66 180 Mhz, how config clock with Config Tools " has sorted thing out. Some things to mention/ponder...

1) Unlike my code your code did not hang at IREFST. The difference was you do not set HGO.

2) I found that 180MHz runs without setting RUNHS. I'm presuming while this is possible, it only when RUNHS is set that 180MHz is guaranteed.

3) Wonder if the Flash issue is because of the elevated voltage in RUNHS mode.

Anyway, thank you,

[mjbcswitzerland]

Hi

Yes it is possible to run at 180MHz in RUN mode (without Flash programming restrictions) but it is not using the processor within its guaranteed specification (over-clocking). It is OK to do this in a hobby project but would not be acceptable in a serious product development and negligent in some products (especially anything that required high reliability or were safety critical in any respects).

Regards

Mark

[mjbcswitzerland · Accepted solution]

Hi

12MHz crystal can be used for 180MHz operation (in HSRUN mode).

http://www.utasker.com/kinetis/MCG.html

See below (simulation of K66 board) with the following settings:

#define CRYSTAL_FREQUENCY    12000000                    // 12 MHz crystal
#define CLOCK_DIV            1                           // input must be divided to 8MHz..16MHz range (/1 to /8)
#define CLOCK_MUL        30                              // the PLL multiplication factor to achieve operating frequency of 180MHz (x16 to x47 possible) [PLL output range 90..180MHz - VCO is PLL * 2]
#define BUS_CLOCK_DIVIDE     3                           // 180/3 to give 60MHz (max. 60MHz)
#define FLEX_CLOCK_DIVIDE    3                           // 180/3 to give 60MHz (max. 60MHz)
#define FLASH_CLOCK_DIVIDE   7                           // 180/7 to give 25.714MHz (max. 28MHz)

Beware of restrictions in HSRUN mode - for example flash programming is not possible.

Regards

Mark