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How to use RTC on FRDM-KL25Z board.

Question asked by Yasuhiko Koumoto on Sep 22, 2014
Latest reply on Sep 23, 2014 by Yasuhiko Koumoto

Hi all,


I am working on FRDM-K20D50M and FRDM-KL25Z boards.

Also I would like to use RTC to make MCU woken up from the low power mode.

In the FRDM-K20D50M case, it seems to be no problem.

However, in the FRDM-KL25Z case, the MCU hangs up when RTC_CR[OSCE] bit is set.

I think the reason would be because no 32kHz OSC was not equipped on the FRDM-KL25Z board,

For your reference, I will show my code below.


void RTC_init(void)
    SIM_SCGC6 |= SIM_SCGC6_RTC_MASK;// by this statement, hard fault becomes not occur

    RTC_CR |= RTC_CR_OSCE_MASK; //<= hanged up at this statement
    RTC_TPR = 0;
    RTC_TAR = 0;
    while((RTC_SR &( RTC_SR_TOF_MASK|RTC_SR_TIF_MASK))!=0);
    RTC_SR |= RTC_SR_TCE_MASK;  //<= although enabled RTC, count does not count up


If 'RTC_CR |= RTC_CR_OSCE_MASK' does not exist, the hanged-up does not occur.

However the overflow interrupt neither occur.

Could anyone let me know how to use RTC on FRDM-KL25Z board?

Otherwise, can RTC not actually be used on FRDM-KL25Z board?


Best regards,

Yasuhiko Koumoto.