https://devzone.nordicsemi.com/f/nordic-q-a/1671/nrf51822-cpu-speedSeeing, that the nRF51822 was specified to operate with a 16 MHz crystal or oscillator. Is that also the clock what the Cortex-M0 core runs or is there a PLL to increase the cpu clock? (Seeing eg. STM32F0 which are running at 48 MHz).en-USTelligent Community 13Fri, 21 Feb 2014 16:52:28 GMThttps://devzone.nordicsemi.com/thread/7398?ContentTypeID=1Fri, 21 Feb 2014 16:52:28 GMT137ad170-7792-4731-bb38-c0d22fbe4515:492aaaa5-7836-4ea1-bcf9-d3101fcbd1f7FormerMember<p>Joe, if you need higher speed you could also use a 32 MHz crystal. After power up with 16 MHz RC oscillator you need to configure the clock module to let it know that a 32 MHz crystal is being used before switching to the crystal. With this configuration, for not so accurate and timing specific tasks you can still use the 16 MHz RC oscillator and save some power.</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/7397?ContentTypeID=1Thu, 20 Feb 2014 11:39:42 GMT137ad170-7792-4731-bb38-c0d22fbe4515:7baa350e-acea-4667-8c2c-b197a8447016Ole Morten<p>Yes, the CPU speed of the nRF51 series is 16 MHz. This speed is fixed, and can not be changed.</p><div style="clear:both;"></div>