NRF51822 can not wakeup from sheep mode with RTC interrupt.https://devzone.nordicsemi.com/f/nordic-q-a/20558/nrf51822-can-not-wakeup-from-sheep-mode-with-rtc-interruptI did not use softdevice; //this my code void SysClk_LFInit(void) { NRF_CLOCK-&gt;LFCLKSRC = (CLOCK_LFCLKSRC_SRC_RC &lt;&lt; CLOCK_LFCLKSRC_SRC_Pos); NRF_CLOCK-&gt;EVENTS_LFCLKSTARTED = 0; NRF_CLOCK-&gt;TASKS_LFCLKSTART = 1; while (NRF_CLOCK-&gt;EVENTS_LFCLKSTARTEDen-USTelligent Community 13Fri, 17 Mar 2017 12:51:10 GMTRE: NRF51822 can not wakeup from sheep mode with RTC interrupt.https://devzone.nordicsemi.com/thread/80147?ContentTypeID=1Fri, 17 Mar 2017 12:51:10 GMT137ad170-7792-4731-bb38-c0d22fbe4515:597c3e44-9f6f-4b24-906d-0d53cb0084dbFormerMember<p>In order for the COMPARE0 to trigger an interrupt, the interrupt needs to be enabled:</p> <pre><code>NRF_RTC1-&gt;INTENSET = RTC_INTENSET_COMPARE0_Msk; </code></pre> <p>In addition, in the the interrupt event should be cleared in the interrupt handler:</p> <pre><code>NRF_RTC0-&gt;EVENTS_COMPARE[0] = 0; </code></pre> <p>Please check if the above suggestions change anything.</p><div style="clear:both;"></div>