https://devzone.nordicsemi.com/f/nordic-q-a/79951/zephyr-ncs-how-to-tell-which-attribute-has-cccd-changedHi, I understand the on_cccd_changed() will be called when CCCD changed. But I can&#39;t figure out which attribute it&#39;s associated with. I try to print out the UUID which is always 2902. The code below is from the NCS BLE tutorial. I have 4 characteristicsen-USTelligent Community 13Fri, 24 Sep 2021 17:22:27 GMThttps://devzone.nordicsemi.com/thread/331152?ContentTypeID=1Fri, 24 Sep 2021 17:22:27 GMT137ad170-7792-4731-bb38-c0d22fbe4515:20d09fb9-96da-4cdc-a106-a3775c9f4583bluebeam<p>Right... what as I thinking. I must be too quick copying and pasting same code block four times and start to wonder how I can tell them apart if they&#39;re calling the same function...&nbsp; :-(</p> <p>Thanks!</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/331112?ContentTypeID=1Fri, 24 Sep 2021 13:29:19 GMT137ad170-7792-4731-bb38-c0d22fbe4515:81acbc3c-23a9-472c-81f3-37c7619d11bbEinar Thorsrud<p>Hi,</p> <p>When you use&nbsp;BT_GATT_CCC that is the CCCD for the characteristic you&nbsp;declared immediately before. To separate between them, use separate callback functions (see for instance&nbsp;zephyr\subsys\bluetooth\audio\vocs.c for an example).</p> <p>When the event handler is called (<code>on_cccd_changed()</code> in your case), you get a pointer to the attribute and the value (first and second parameter to the callback function respectively).</p><div style="clear:both;"></div>