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RTC using external clock source on EXTAL0 on Kinetis L25

Question asked by Eyal Doron on Jun 17, 2014
Latest reply on Jun 17, 2014 by Dragos GALALAE

Hi all,

I'm confused concerning the RTC clocking. I want to input an externally-supplied 32kHz clock signal into EXTAL0 and run the KL25 in FEE mode. I also want the RTC to operate, both in run and in Stop mode. What is confusing to me is the following:

1) Both the OSC and the RTC peripherals contain register flags which control oscillator on/off and loading capacitors. However, in the KL25 there is only one oscillator (there is no separate RTC oscillator like in the K series devices). The system oscillator is controlled by the OSC0_CR register flags. So, what are the RTC register flags in RTC_CR controlling?

 

2) Suppose I set the system oscillator in bypass mode, and input a 32kHz signal into EXTAL0. I can also configure the system oscillator to remain on in low-power modes. Can I then run the RTC using the OSC32KCLK input clock?

 

Thanks,

Eyal Doron

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