https://devzone.nordicsemi.com/f/nordic-q-a/84353/nrf52840-systick-external-clock-sourceHello Question: On what clock/clock-speed does the system tick timer run, when configured to use the external clock instead of the CPU clock? I&#39;ve seen a couple of threads discussing the system tick timer using the processor clock (CPU clock)en-USTelligent Community 13Fri, 04 Feb 2022 08:54:46 GMThttps://devzone.nordicsemi.com/thread/351243?ContentTypeID=1Fri, 04 Feb 2022 08:54:46 GMT137ad170-7792-4731-bb38-c0d22fbe4515:f6b7efa2-8718-424f-adcc-18e3a930ec0aAmanda Hsieh<p>Hi,&nbsp;</p> <p><span>ARM&#39;s documentation for the&nbsp;Cortex-M Systick can be found&nbsp;</span><a href="https://developer.arm.com/documentation/dui0553/b/?lang=en">here</a><span>.</span><span></span></p> <p><span>-Amanda</span></p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/351158?ContentTypeID=1Thu, 03 Feb 2022 14:34:31 GMT137ad170-7792-4731-bb38-c0d22fbe4515:3f9d6551-9c81-4151-90ed-0d17eed40702M. David.<p>Ok. But&nbsp;if&nbsp;Iconfigure the&nbsp;CLKSOURCE of the&nbsp;<span>SysTick</span><span>-&gt;</span><span>CTRL register 0, does this mean:</span></p> <p>- undefined behaviour</p> <p>- its runing on the CPU clock speed</p> <p><pre class="ui-code" data-mode="text">SysTick-&gt;CTRL = SysTick_CTRL_ENABLE_Msk;</pre></p> <p></p> <p>Is this documented anywhere?</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/351081?ContentTypeID=1Thu, 03 Feb 2022 12:03:48 GMT137ad170-7792-4731-bb38-c0d22fbe4515:f32916bd-947f-4018-885d-392397d972cbAmanda Hsieh<p>Hi,&nbsp;</p> <p>Unfortunately,&nbsp;it <span>only supports CPU clock.&nbsp;&nbsp;</span></p> <p><span>Regards,<br />Amanda</span></p><div style="clear:both;"></div>