Custom PCB with BMD380 SWD with NRF52840 DK v3.0.2

[Arshad Khan]

I am trying to program a custom PCB board that has a BMD380 (10059 chip). The BMD380 is setup in HV mode and is powered by a Li-Ion battery (please see the schematic below). 

The DK board is NRF52840-DK v3.0.2. 

Until now we have no way to tell why the external board is not picked by the SWD. Here is what we did: 

Case 1: Powering External Board with Li-Ion: 

NRF DK Board (P20)   ->   External BMD380 PCB 

SWD I/O (P20) ---> SWDI/O 

SWD CLK P(20) --> SWDCLK

GND  (P1) --> GND  

RESET  (P20) --> RESET  

SWD_SET ----> VCCMCU (1.8V) 

P.S: I don't see a GND_DETECT pin (there is no label on the pin below RESET pin on P20 in v3.0.2) but to be sure, I connected that pin to GND with the external board. 

No external board is detected on NRF Connect App for Desktop (Programmer) as well as on nrfjprog (cmd: nrfjprog --famy NRF52 --recover --log). NRFJProg programs the on DK NRF. Please see image below for NRFJprog output: 

Case 2: Power External Board with NRF52840 DK board

After not able to get the external board on SWD and searching this forum for the answers, I stumbled upon the correct documentation of the v3.0.2 which states that If SB47 is connected, then VDD_nRF on P20 can power the external board and SWD won't see the on-DK NRF chip. This is not true really. When I soldered the SB47, I can still see NRF (even before I connect anything from external board PCB). 

Ignoring the above ambiguity (and out for glory), I powered the external PCB with VDD_nRF as follow: 

NRF DK Board (P20)   ->   External BMD380 PCB 

SWD I/O (P20) ---> SWDI/O 

SWD CLK (P20) --> SWDCLK

GND (P1) --> GND 

RESET (P20) --> RESET 

VBAT ----> VDD_nRF (P20)

SWD_SET (P20) ----> VDD_nRF (P20, on DK board)  

NOT LABELLED PIN after RESET on P20 ---> GND (P1) 

Soldered SCB47 (just below the DEBUG_OUT connector physically). 

Unfortunately in this case the DK board still sees internal NRF chip but sometimes the NRFJProg output has changed (see below): 

Can anyone please help me understand what I might be doing wrong? 

My goal is to upload a boot loader with serial and BLE DFU enabled, and DFU triggers enabled and then not use SWD again. 

P.S: If necessary, I do have a bunch of NRF52840 USB dongle that I can use to check if SWD on DK is working, please let me know if it's worth trying that? 

thank you, much appreciated. 

[Kazi Afroza Sultana]

Hello,

Have you checked the voltage level of your custom board as if it as same as DK? 

[Arshad Khan]

Hi Kazi, 

Initially it was not. The SWDIO and VDD on the DK board were 3 and 3.1V respectively (for case 1, where custom PCB is powered externally) and the board is at 1.8V. 

After reading a few more post on this forum, one suggested that either to connect SWD_SEL to VDD on the custom board i.e., at 1.8V and it will shift the SWDIO and CLK to 1.8V. I tried that but that did not work, the SWDIO pin remains at 3V. 

Then another post suggested to power the DK board with J3 and move the power switch on USB (https://devzone.nordicsemi.com/f/nordic-q-a/92524/unable-to-program-a-blank-nrf52840/396680) and doing that made all SWDIO and VDD and everything on 1.8V (that is same as custom board VDD). After that I connected my custom PCB board which already is powered externally and is at 1.8V. This did not work as well. 

Please let me know if you need any more information before you can suggest what could be wrong. 

Thank you. 

[Kazi Afroza Sultana]

Hello,

The error is related to the debug probe. It seems that debug probe can not communicate correctly to the target; still it's not powered properly. It would be helpful to watch the setup and your connection.

''Initially it was not. The SWDIO and VDD on the DK board were 3 and 3.1V respectively (for case 1, where custom PCB is powered externally) and the board is at 1.8V. ''

This will not work as you know the target and the DK board must have same power level. 

Also, can you try to use debug out pin P19 to program the external board? source: Debug output

[Arshad Khan]

Hello, 

thank you for your suggestion. I ended up getting a programmer instead of using the NRF52840-DK board, mainly because my BMD-840 ublox was set to HV mode (1.8V) and I was unsure if different voltages could power the target as well as provide SWD Data/Clock at 1.8V without level shift (I'd assume that if UICR register is set to 1.8V for onchip NRF52840 on the DK board and it is getting powered from the USB, it should be able to do it. But that was not working). 

Anyhow, the programmer (JLink) works great. Thank you.