NRF52840 DK Debug Out SWD @ 3.3V

[Mar840]

Hi, I have some questions about the NRF52840 DK Debug out header using P20 NOT P19 : https://docs.nordicsemi.com/bundle/ug_nrf52840_dk/page/UG/dk/ext_programming_support.html

1) Is SH_VTG needed? In other answers they say: connect it with VDD nRF.

Source : Yes, P20 on the DKs has had some naming changes (VTG is now called SWD SEL) since the last revision, as we now have an nRF5340 as the debugger MCU. What has changed is that GND is used to detect an external board instead of the voltage like on older revisions. Link: devzone.nordicsemi.com/.../flashing-and-debugging-an-external-nrf52840-board-with-the-nrf52840-dk-different-to-those-covered-in-forum

That was over 2 years ago, are they talking about a different version because versions differ :  nRF52840-DK - Debug Out differences from v2.0.2 to v3.0.0 

2) What is the difference between VDDnRF and VDDnRF'?

3) To program a external nrf chip with the DK with 3.3V ; can I use the NRF52 on the dev board in high voltage (VDDH = 5V) and let VDD(nrf) = 3.3V. Thanks to the voltage follower the VDD is going to be 3.3V and the interface chip(program/debug chip) is programming my board with 3.3V, is this correct? Some say VDD is always 3V (but then this means you are using the DK in high voltage mode, and then it will be a problem that VDD and VDD_nRF are connected together, since the VDD will always be 3V because of the voltage regulators within the DK. link :  nRF52840 DK v3.0.0: VDD vs VDD_nRF  ) but that is not correct I think. If not, what is the voltage follower doing? I want to only connect GND/SWDIO/SWDCLK to my external board with the nrf52 that I want to program. 

4) Why is pin 8 : SH_GND_DETECT Ground detect (P20) not printed on the pcb (version 3.0.2) ? Is it necessary to connect it? To where? 

  

Thanks in advance!

[Priyanka]

Hi Marijn,

1) Is SH_VTG needed? In other answers they say: connect it with VDD nRF.

In the newer revisions, this is the SWD_SEL (as shown in the picture of the DK that you have attached) and if you are powering your external board from the DK, then you need to connect the VDD_nRF' to the SWD_SEL. 

2) What is the difference between VDDnRF and VDDnRF'?

As mentioned above, the VDD_nRF' is the power domain of the entire DK and thus connect this to SWD_SEL in case you need to power the external board from the DK, whereas the VDD_nRF is the power domain of just the nRF52840 chip.

3) To program a external nrf chip with the DK with 3.3V ;

Please take a look at the NOTE mentioned in Product Specification:

4) Why is pin 8 : SH_GND_DETECT Ground detect (P20) not printed on the pcb (version 3.0.2) ? Is it necessary to connect it? To where? 

In previous versions the GND_DETECT was used to select the voltage, whereas in the newer versions it's used to detect an external board. So you can directly connect the GND of the external board to the GND on the DK.

Regards,

Priyanka

[Mar840]

Hi, it's much clearer for me now, thank you!