Programming External Board using NRF52840-DK

[Belalshinnawey]

I am using the NRF52840-DK REV2 to program my custom board. I am using the debug out port and connecting it to my custom board, I tried both powering the custom board through the DK or externally, I even shorted the SB47 and still having the same issue. I can't get any debug messages on my terminal after "Starting target CPU". I'm using the NRF connect sdk v2.0.0.

Here is what the issue is

When I flash the software (Just a simple blinky) I get no results, the terminal says flash successful. but the LED doesn't blink.

When I use debug mode, the LED blinks correctly. I can disconnect the custom board from the DK and the led still blinking, I can reset the board and the LED still blinking, I cannot disconnect the board and reconnect it, if I do that it no longer blinks. Can someone explain what is this?

[nRF5xFanboy]

Hi Betalshinnawey,

Just some thoughts :
- THe debug port on the nrf52840-DK does not power the external board over the debug port (see the hardware drawing on infocenter).

- Are you sure you did flash your external board and not the MCU on the development kit board?   What cable do you use tag-connect ?

- Are you developing software based on NCS using zephyr  or without zephyr?
   If you use ncs+zephyr please make sure to enable the RTT longing in the proj.config


Best regards,
    nRF5xFanBoy

[Belalshinnawey]

I am using the tag connect cable, I also gave up powering the board from the debug port, I am connecting an external power supply 3V to my external board. When I am using the debug mode, the led on my board is blinking so I know the application is running correctly when I am using debug, however, if I try to use flash without debugging the led doesnt blink. when debugging, the program doesnt persist after I disconnect and reconnect power.