I used 52840 act as center device.whose RX TX connected to my another MCU(MTK7688 UART). This is a IoT-GateWay. now I want to upgrade the 52840 application. BUT, I can not find how to do.because you give methods that only about using cellphone app. what can I do next? thanks.
We do have support for serial DFU over UART. Please take a look at the SDK documentation here: DFU protocol and also this blog post https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/getting-started-with-nordics-secure-dfu-bootloader to get started.