https://devzone.nordicsemi.com/f/nordic-q-a/74564/why-the-program-can-switch-to-bootloader-from-app-sleep-modeHi guys. I flashed a uart-dfu Bootloader(SDK-location\nRF5_SDK_15.0.0_a53641a\nRF5_SDK_15.0.0_a53641a\examples\dfu\secure_bootloader\pca10056_uart), when the program run in APP(ble_app_uart) enviroment, I pressed button 1 made the app enter sleep modeen-USTelligent Community 13Thu, 29 Apr 2021 14:38:39 GMThttps://devzone.nordicsemi.com/thread/307534?ContentTypeID=1Thu, 29 Apr 2021 14:38:39 GMT137ad170-7792-4731-bb38-c0d22fbe4515:a9f4618d-b8bb-4a23-bfe4-3123a7e9da79Vidar Berg<p>Hi,</p> <p>The bootloader starts before the application on startup (e.g. after a wakeup from System OFF reset - see my answer in your other post <a href="https://devzone.nordicsemi.com/f/nordic-q-a/74577/the-program-time-sequence-when-52840-poweron">here</a>), and it detects that button 4 is pressed.</p><div style="clear:both;"></div>