https://devzone.nordicsemi.com/f/nordic-q-a/102207/question-about-the-value-of-p_ble_evt--header-evt_idhello, If you look at the function below in nrf_sdh_ble.c, &quot; printf(&quot;BLE event: 0x%x.&quot;, p_ble_evt-&gt;header.evt_id); &quot; shows the value of &#39;p_ble_evt-&gt;header.evt_id&#39;. If you check the value for the connection status in the terminal window, en-USTelligent Community 13Tue, 25 Jul 2023 11:38:09 GMThttps://devzone.nordicsemi.com/thread/438055?ContentTypeID=1Tue, 25 Jul 2023 11:38:09 GMT137ad170-7792-4731-bb38-c0d22fbe4515:0d4ba7c8-12d5-44da-95ac-49dbd962f012Hung Bui<p>Hi PRK,</p> <p>0x10 =&nbsp;BLE_GAP_EVT_CONNECTED</p> <p>0x55 =&nbsp;<span>BLE_GATTS_EVT_EXCHANGE_MTU_REQUEST</span></p> <p>If you take a look at ble_ranges.h you can find this:&nbsp;<br /><img style="max-height:240px;max-width:320px;" src="https://devzone.nordicsemi.com/resized-image/__size/640x480/__key/communityserver-discussions-components-files/4/pastedimage1690284900858v1.png" alt=" " /></p> <p>They are the event base. So 0x10 will be long to BLE_GAP_EVT_BASE. And in ble_gap.h you will find the events with the base 0x10:&nbsp;<br /><img style="max-height:240px;max-width:320px;" src="https://devzone.nordicsemi.com/resized-image/__size/640x480/__key/communityserver-discussions-components-files/4/pastedimage1690284954741v2.png" alt=" " /></p> <p></p> <p>For 0x55, it belongs to&nbsp;BLE_GATTS_EVT_BASE (0x50) and in ble_gatts.h you will find that, start from 0x50,&nbsp; 0x55 is equal to&nbsp;BLE_GATTS_EVT_EXCHANGE_MTU_REQUEST</p> <p><img style="max-height:240px;max-width:320px;" src="https://devzone.nordicsemi.com/resized-image/__size/640x480/__key/communityserver-discussions-components-files/4/pastedimage1690285025414v3.png" alt=" " /></p> <p></p><div style="clear:both;"></div>