https://devzone.nordicsemi.com/f/nordic-q-a/86069/nrf52840-dfu-mapsdk nRF5_SDK_17.0.2_d674dde I used some flash to store data. But before dfu,it was equal to (FF FF FF FF FF FF FF FF|........) and after dfu,it was equal to (29 48 0C F0 FC FD 29 49|)H....)I) It was changed after dfu. I used flash adder:0x3e000en-USTelligent Community 13Tue, 22 Mar 2022 12:39:15 GMThttps://devzone.nordicsemi.com/thread/359365?ContentTypeID=1Tue, 22 Mar 2022 12:39:15 GMT137ad170-7792-4731-bb38-c0d22fbe4515:7236a9f7-9553-46b3-be6c-18346c8bb7f3Einar Thorsrud<p>Hi,</p> <p>During DFU, the nRF5 SDK bootloader will do a dual bank update if there is enough space for it, where it uses the available space between the end of the application and the beginning of the bootloader. However, the bootloader can be configured to lay off a configurable amount of pages, counting down from immediately below the bootloader. This is for instance where FDS pages are located, and also where you should locate any other flash page that you use for persistent storage (make sure they are below FDS pages again if that is used). Then, you need to adjust the&nbsp;NRF_DFU_APP_DATA_AREA_SIZE define in the bootloader&#39;s sdk_config.h so that it covers all the&nbsp;reserved flash pages. With this, the&nbsp;bootloader will never write to those pages.</p> <p>PS: See <a href="https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.1.0/lib_bootloader.html#lib_bootloader_memory">Memory layout figure</a>&nbsp;to get a better overview of this.</p><div style="clear:both;"></div>