nRF52840 DK Switching Shield Debug (P20)

[WestCoastDaz]

I would like to use the Shield Debug (P20) on the nRF52840DK as part of a Device Under Test platform for production devices.  I also want to be able to transmit/receive data to/from the nRF52840 on the DK as this will be running a test program which is checking the functionality of the Device Under Test.

1. Should the signals SH_VTG, SH_SWDIO, SH_SWDCLK and SH_GND_DETECT be isolated from the DUT and switched into circuit only when the DUT needs to be programmed?
2. Which signal is actually responsible for causing the interface micro to switch to the SH_XXX signal path?  Is it the presence of voltage on SH_VTG or SH_GND_DETECT being pulled to ground?

Thanks,

[Einar Thorsrud]

Hi,

The P20 header is there so that you can debug an external device (like a shield). The purpose of the GND_DETECT is so that the onboard debugger can know if it should use the pins connected to the onboard nRF5 device, or it it should use the pins on the P20 and debug out port instead. See Debug output.

[WestCoastDaz]

So if GND_DETECT is pulled low then those SH_SWDIO and SH_SWDCLK are used?  Does SH_VTG also need to have voltage on it for those pins to work?

Thanks,

[Einar Thorsrud]

Hi,

WestCoastDaz said:

So if GND_DETECT is pulled low then those SH_SWDIO and SH_SWDCLK are used?

Yes, that is correct.

WestCoastDaz said:

Does SH_VTG also need to have voltage on it for those pins to work?

Yes, SH_VTG should be connected to VDD on the external board/shield. I assume the board is powered from elsewhere, if not you also need to connect the same point to VDD on the DK. (That also reminds me to mention that unless there is another connecting ensuring a common ground, then you need to connect SH_GND_DETECT to GND on the DK as well.)