RE: nRF52840 cannot enter DFU mode without UART RX pull high

Dwight Fowler — Mon, 30 Oct 2023 17:51:36 GMT

yesheng, Jørgen thanks for the insight. We are running into the same issue, and need a software solution. You may have saved our project.

RE: nRF52840 cannot enter DFU mode without UART RX pull high

yesheng — Tue, 27 Sep 2022 01:12:19 GMT

Hi Jørgen,

I see, thanks for the explanation. I added a 47k pull-up and it works great.

Thanks,

RE: nRF52840 cannot enter DFU mode without UART RX pull high

Jørgen Holmefjord — Mon, 26 Sep 2022 13:32:28 GMT

Hi,

If UART RX pin is left floating when the UART peripheral is enabled in RX mode, the peripheral will normally generate one or more errors, see Error conditions:

"An ERROR event, in the form of a framing error, will be generated if a valid stop bit is not detected in a frame. Another ERROR event, in the form of a break condition, will be generated if the RXD line is held active low for longer than the length of a data frame. Effectively, a framing error is always generated before a break condition occurs."

By default, the serial DFU transport implementation pass the error codes to the APP_ERROR_HANDLER() macro if they occur, see "nRF5_SDK_17.1.0_ddde560\components\libraries\bootloader\serial_dfu\nrf_dfu_serial_uart.c:150". It is possible to modify this code to not pass the error to the error handler, or just a subset of the possible error sources, but note that this will affect all your DFU UART operations, not just when starting the bootloader.

Why do you not want to have a pullup on the RX pin?

Best regards,
Jørgen