nrf52840 DK description and schematic do not agree for external debug port P19

[PaulJ]

I am attempting to connect my nrf52840/52811 DK to my custom PCB that contains nrf52840. The DK users guide describe the connections on the P19 debug out port but I can see on the schematic for the DK that something is incorrect. Specifically, the UG says that Pin1 is "EXT_VTG" and is used to select this port for debugging by connecting a 3V level. The schematic shows pin1 as an optional "power out" to my custom PCB and is not connected to anything if I don't short one of the two solder bridges. Also, the schematic shows that pin 3 is a "select" pin while the UG claims that this is GND. The UG also says that pin 9 is an "EXT_GND_SEL" but doesn't explain what this is for!

Can anyone tell me the correct pin functions for this port and also confirm that the "select" function is done with a 3V level? It would have made more sense to me to have the "select" function done with a connection to ground so just want to make sure I have that right!

[PaKa]

The nRF52840 DK user guide hasn't been updated to match the latest DK version. You can check out the nRF52 DK user guide for how to use P19/P20 for programming external targets. Note that the external target must have same operating voltage as the DK.

[PaulJ]

Thank you for the information. I looked at the nRF52DK UG and the section on "DEBUG OUT" does not have much detail. It does say that "If the interface MCU detects target power on both P19 and P20, it will by default program/debug the target connected to P19" but then it doesn't tell me which pins I use to apply this 3V to. I thought that maybe they just copied the standard J-Link interface but that doesn't seem to have any pin assigned to a power source. I am surprised that Nordic would be providing a piece of hardware (the nRF52840 DK) but not also provide an accurate description of how to use it. I would be a bit leery of using the description obtained from a different piece of hardware; especially now that I know that the documentation provided by Nordic is a bit "sloppy"! I don't want to start applying power randomly to pins since that could cause the magic smoke to leave my hardware!

[PaulJ]

I dug a little deeper and can see that others are having the same problem. One of the sites gave me a link to the schematic for the nRF52 DK. Can you confirm that the pinout of P19 on my nRF52840/52822 DK is the same as P19 on the nRF52 DK? Here is the pinout from the nRF52 DK:

Please also confirm that the "select" function is 3.0V applied to pin 3 from my custom PCB and that the "reset" is an active low (i.e. nReset). 

I suppose I should also confirm what rev level this pinout change occurred at. I will then check my DK rev level to ensure it is valid.

Thanks again

[PaKa]

Pinout between the latest nRF52 DK and the latest nRF52840 DK is the same yes. All pins are referenced to the VDD of the device and that can change depending on the DK setup so it's not always 3.0V. If you set up a nRF52840 DK to use the 5V option to power through VDDH then the VDD is by default 1.8V.

[PaulJ]

Also, since the published nRF52840/52811 DK Users Guide is not accurate, can you please let me know the current method that allows me to set the system operating voltage for the DK? My custom PCB runs on 3.0V so I will need to change the DK to match so my debug signals are the correct level.

[PaulJ]

Please also confirm that I must apply a 'high" level on pin3 of the interface to "select" the debug out function.

[PaKa]

If you run the board in "VDD" mode then the voltage will be 3V. If you move to USB or Li-Po then the voltage will be controlled by the regulator setting in the target device on the DK, default is 1.8V but that can be changed by the SW in the device.

When using the 10 pin header P19

When using the 8 pin header P20