https://devzone.nordicsemi.com/f/nordic-q-a/25812/how-to-match-bluetooth-4-when-using-data-length-extensionHi, I&#39;m using nRF52840. I would use data length extension and set the MTU size to 247 when it works as peripheral. However,there would be some problem when it connect to the phone which just support bluetooth 4. So how to match bluetooth 4 when usingen-USTelligent Community 13Wed, 11 Oct 2017 09:09:57 GMThttps://devzone.nordicsemi.com/thread/101663?ContentTypeID=1Wed, 11 Oct 2017 09:09:57 GMT137ad170-7792-4731-bb38-c0d22fbe4515:9e3a947b-ce24-4d16-8453-08d17d0ba643MartinBL<p>Q1) When two phones with different BLE versions connect they negotiate the optimal settings. It doesn&#39;t matter if it is phones with BLE 4.0, 4.1, 4.2, or 5.0. If one device doesn&#39;t support all the new features the agree to use only the old features. They will use the lowest common denominator, so to speak.</p> <p>There is one exception though. BLE 4.x devices cannot connect to BLE 5 devices that advertise with 2M data rate or coded phy. The same goes for two BLE 5 devices if they don&#39;t use the same phy. However, it is possible to connect on a certain phy and then change phy on the fly after they have connected to improve range or speed.</p><div style="clear:both;"></div>