KL05 Clock

[danreltek]

I have a FRDM-KL05Z board and I noticed something peculiar that's bothering me.

The fastest crystal on the board 8.0 MHz.

Yet one of the LED blink projects (in Keil uVision, I think) uses a delay loop that simply increments a local variable. I doesn't use any system timer or interrupt.

The trouble is that given the numbers it is counting to, there is no way it should be able to do this in the time it actually takes. It seems like it is actually running at its max speed of 48Mhz.

Is there a clock multiplier on chip or some other internal reference?

Thanks

Dan

[Alice_Yang]

Hi Dan,

There are not only one multiplier on the chip,

The selection and multiplexing of system clock sources is controlled and programmed via

the MCG module. The setting of clock dividers and module clock gating for the system

are programmed via the SIM module.

I suggest you firstly see the Clocking diagram(see screenshot below)(KL05RM->p106).

And we can choose clock source from these :

Hope it helps

Alice

[danreltek]

Thanks Alice,

So this seems to suggest that when I come to designing a purpose built PCB, I do not have to use any external crystal if I use the 4MHz IRC.

Is that true? If so, I like it a lot!

Regards

Dan

[Alice_Yang · Accepted solution]

Hi Dan,

Yes, you can calculate it according the clocking diagram above and check the Reference Manual ,

Check whether 4MHz can meet your need, if yes , you need not to use external crystal .

Best Regards,

Alice

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[danreltek]

Great!

Thanks Alice

[Alice_Yang]

You are welcome !