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

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

PaulJ — Thu, 27 Mar 2025 21:49:05 GMT

I can confirm that the reset signal is active low. I monitored on the scope while the system was programming and configuring and it normally sits high with an occasional drop to low.

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

PaulJ — Thu, 27 Mar 2025 15:16:52 GMT

Hi Kenneth. Yes, that is true. However, the signals routed to the Debug Out connector come from the "interface MCU" so they could potentially be either polarity. I suspect that it is an active-low, but nowhere in the literature is this explicitly stated. I have it currently connected as an active low, and since I also now have the "select" line pulled low (instead of high as all the published documentation tells me), I can now program the part on my custom PCB. I am still having issues getting the debugger to start but I think I may need to adjust my RC values on the reset line for faster response. That's todays project!

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

Kenneth — Thu, 27 Mar 2025 13:13:25 GMT

The nRF52840 has an active-low reset pin.

Kenneth

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

PaulJ — Wed, 26 Mar 2025 16:03:52 GMT

Thank you for the updated pin description table. I would encourage you to press Nordic to update the online version of the DK User Guide so other users will not have the same experience as me! Much time and money has been wasted by this inaccurate information!

One last question (hopefully) that has not been answered: is the 'reset' active high or active low? This information should be added to the UG as well.

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

PaKa — Wed, 26 Mar 2025 10:19:59 GMT

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

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

PaulJ — Tue, 25 Mar 2025 15:45:32 GMT

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

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

PaulJ — Tue, 25 Mar 2025 15:43:48 GMT

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.

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

PaKa — Tue, 25 Mar 2025 09:53:31 GMT

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.

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

PaulJ — Mon, 24 Mar 2025 16:01:40 GMT

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

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

PaulJ — Mon, 24 Mar 2025 14:21:12 GMT

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!

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

PaKa — Mon, 24 Mar 2025 09:27:49 GMT

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.