https://devzone.nordicsemi.com/f/nordic-q-a/15462/why-nrf51422-have-problem-with-timerwithout timer it work fine but when i use timer it goes here. my timer code is this #define APP_TIMER_PRESCALER 0 /**&lt; Value of the RTC1 PRESCALER register. */ #define APP_TIMER_MAX_TIMERS 6 /**&lt; Maximum number of simultaneously created timersen-USTelligent Community 13Sat, 06 Aug 2016 06:11:41 GMThttps://devzone.nordicsemi.com/thread/59055?ContentTypeID=1Sat, 06 Aug 2016 06:11:41 GMT137ad170-7792-4731-bb38-c0d22fbe4515:f26955cc-484f-41db-a146-33cedfeeda7cnavid<p>that was helpfull . thanks</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/59054?ContentTypeID=1Fri, 05 Aug 2016 16:48:45 GMT137ad170-7792-4731-bb38-c0d22fbe4515:50ee7d7a-6cc1-48be-aa76-a6daa0158c9aStefan Birnir Sverrisson<p>Hi navid</p> <p>Not sure actually. Have you tried to increase APP_TIMER_MAX_TIMERS or APP_TIMER_OP_QUEUE_SIZE constants, just to see if that makes a difference? Have you enabled the RTC1 in nrf_drv_config.h file (The application timer library uses RTC1 in the background). To find out what is wrong, you could check if there is any error code thrown. Start debugging as described on <a href="https://devzone.nordicsemi.com/question/60125/my-device-is-freezing-and-restarting/?answer=60126#post-id-60126">this thread</a> and <a href="https://devzone.nordicsemi.com/blogs/821/an-introduction-to-error-handling-in-nrf5-projects/">this thread</a>. Also, make sure the priority of RTC1 is APP_IRQ_PRIORITY_LOW, which should be set in the nrf_drv_config.h file in your project folder.</p><div style="clear:both;"></div>