https://test-devzone.nordicsemi.com/f/nordic-q-a/88022/questions-about-external-app-dfuI&#39;m working on a system that has an nRF52 and another ARM microcontroller. We have communication between the two over UART, and I want to use the external app functionality, and just want to double check some of the modifications that I&#39;m making to theen-USTelligent Community 13 Non-ProductionWed, 18 May 2022 14:28:57 GMThttps://test-devzone.nordicsemi.com/thread/368420?ContentTypeID=1Wed, 18 May 2022 14:28:57 GMT137ad170-7792-4731-bb38-c0d22fbe4515:1c922260-5316-4268-b452-cebc2ba09792user104300<p>Through more experimentation it looks like it&#39;s impossible to force a single bank update when using an external app, so we&#39;re going to have to store the external app in external flash, which we have kind of working.</p> <p>That thread does have a lot of good information.</p><div style="clear:both;"></div>https://test-devzone.nordicsemi.com/thread/368416?ContentTypeID=1Wed, 18 May 2022 14:22:50 GMT137ad170-7792-4731-bb38-c0d22fbe4515:3084354e-df83-43a1-9977-9f5b1a932b4duser7377<p>Hi,</p> <p>I am unfortunately not able to explain the resoning for this, primarily because&nbsp;the external app is only partially supported in the example&nbsp;bootloader. So you are required to make some adjustments, both because it is incomplete and to make it fit with your&nbsp;specific use case/external MCU. You may find <a href="https://test-devzone.nordicsemi.com/f/nordic-q-a/68413/how-to-use-external-app-firmware-update/">this thread</a> useful, though.</p><div style="clear:both;"></div>