RTC_CLKIN and RTC_CLKOUT pins assignment on Kinetis

[yujiegou]

Do anyone noted that the RTC_CLKIN and RTC_CLKOUT pins assignment on Kinetis?

For example, on KL25Z (LQFP80),  RTC_CLKIN is assigned on pin1 and RTC_CLKOUT is assigned on pin pin56,

how to route if the user place one external 32k crystal in his PCB board?

[Paul_Tian · Accepted solution]

Hi, Yu Jie

Pin RTC_CLKIN is used to provide clock source for RTC. Pin RTC_CLKOUT is a output of RTC clock. So if you want to give a clock source to RTC_CLKIN, I think you cannot use crystal but oscillator.

Hope my reply can help you.

Best Regards

Paul

[yujiegou]

Hi Paul,

Thanks for your quick respons.

It is a pity KL could only use one oscillator but not crystal, this would be high cost and high current consumption.

Thanks again.

Mark

[dereksnell]

You can use a crystal with the Kinetis oscillator, and clock the RTC from that.  The oscillator uses the pins XTAL and EXTAL to connect to a crystal.  In Kinetis L, the system oscillator can use a 32kHz crystal, and clock the RTC.  Refer to the Clock Distribution chapter in the Reference Manual for more details

[diegocolombo]

Yes Derek,but say that you want to use USB, that need 48MHz or submultiple of it,and RTC too..

I think that in this case at least an oscillator is needed

it could be for 32768 Hz for RTC_CLKIN or 48MHz for USB_CLKIN

Do you confirm?

Regards

Diego