Programing extrnal NRF52840

[matija66]

Hi,

I am trying to program an extrnal nrf52840 it is Minew MS88SF2, I did exactly as desribed here at least I think I did, but unfortunatly it always programs the internal NRF. I measured power supply voltage on external NRF and double cheked connections with multimeter it seems OK. I am using Mbed Studio.

Do you have any suggestions what else can I try?

Thank you very much.

Also I should mention I am able to program board using J-link EDU mini and NRF connect.

[Marjeris Romero]

Hi,

Sorry for the late reply. Have you powered the external board as well? What voltage are you using? The external board needs to be powered up with the same voltage as the DK (normally 3 V).

If you have another 10-pin cable you can try to connect it to the 'Debug Out' pin P19 directly.

[matija66]

Thank you very much for your reply,

Here is the schematics which I used to connect my external target in that manner voltage to my target comes from DK.
What I also tried is I unplugged everything and short soldered SB47 bridge as mentioned in nRF52840 Development Kit User guide (appended printscreen) this should prevent me from programming onboard SoC but it didn't, programming went through normally as always.
Do you have any idea what else could be the problem?

[Marjeris Romero]

Hi,

Are you applying any voltage to the VTG pin on P20? You can do this by shorting P20, pin 2 and 3, as this will force the interface MCU to externally program on P20 (choose SH_ interface).

You can then should be able to power your external board from "VDD_NRF" (P20, pin 1), remember to remove the battery first. You shouldn't need to short SB47 since you are not powering your external board through P19.

If SB47 is shorted then VGT will be connected directly to VDD, and the interface MCU will detect the external board is connected since there is voltage on VTG (P19) and will choose this SWD port as an output for programming/debugging. It should not be possible to program the internal chip then.

There are 3 SWD interfaces on the interface MCU (segger j-link chip), with prefixes SH_,EXT_ and OB_, OB goes to the on-board nRF52 chip, SH_ to P20 and EXT_ to P19.

The interface MCU uses the VTG pins to decide which interface to use for programming. So if EXT_VTG is high it will output on EXT_ interface, if neither of the pins are high then OB_ is default. You can test the voltage on EXT_VTG on P19.

Best regards,

Marjeris

[matija66]

Hello,

Thank very much for your answer.

So in theory if I short pin 2 & 3 of the interface P20 and don't connect anything else programming of onboard nRF should not be posible. Is this correct? Because in my case it is not, on board nRF is always programmed.

Best regards.

Matija

[Marjeris Romero]

Hi,

Have you double checked the voltage on the external board? Can you attach a new picture of your setup so I can help you debug?

BR,

Marjeris

[matija66]

Hello,

Yes, I checked the voltage it is ~3V, here are two pictures from the setup, all connection has been checked with multimeter.

Best regards.

Matija

[matija66]

Hello,

Do you maybe have any suggestions what else could I try? is it possible that Dev. board is faulty? We are running out of time on the project and if no solution I will order a new board or programmer from Segger.

Thank you vey much for your help.

Best regards.

Matija