https://devzone.nordicsemi.com/f/nordic-q-a/74592/how-to-switch-to-bootloader-dfu-mode-when-the-program-run-in-an-appHi guys: a. I use a uart dfu bootloader(loacation: SDK-location\nRF5_SDK_15.0.0_a53641a\nRF5_SDK_15.0.0_a53641a\examples\dfu\secure_bootloader\pca10056_uart) in 52840 soc. b.I flashed the bootloader and SoftDevice by nrfjprog firstly.(cmd: nrfjprogen-USTelligent Community 13Thu, 29 Apr 2021 12:38:55 GMThttps://devzone.nordicsemi.com/thread/307486?ContentTypeID=1Thu, 29 Apr 2021 12:38:55 GMT137ad170-7792-4731-bb38-c0d22fbe4515:8217a3b8-69c3-4299-a6e6-485e76baa6b1Einar Thorsrud<p>Hi,</p> <p>To enter DFU mode from the app you need to ensure that the sdk_config.h of the bootloader has&nbsp;NRF_BL_DFU_ENTER_METHOD_GPREGRET set to 1. The, just write a magic word () to the retention register and reset, as described in <a href="https://devzone.nordicsemi.com/support-private/support/267856#permalink=651850">this post</a>.</p><div style="clear:both;"></div>