Understanding NANO 33 BLE schematic

[Loverboy7000]

Hey guys,

I´m trying to understand all components on the NANO 33 BLE board. Most of them are quite obvious, but some I dont quite understand. I hope you can help me.

Looking at the top right sections of the schematic, where the RESET button sits is a component marked J3.
I assume those are the 5 dots on the bottom of the board. Can I understand that as some form of ICSP port? If so it doesnt seem to follow standard pinout for an ICSP port as described here:
https://www.arduino.cc/en/Tutorial/ArduinoISP

A bit lower are 2 components marked U4A and U4B, that I can´t associate at all. There is a comment next to it saying Crypto Auth.
Does someone know what kind of components those are and what their function is?

Thanks for your help!
Andre

[pert]

Looking at the top right sections of the schematic, where the RESET button sits is a component marked J3.
I assume those are the 5 dots on the bottom of the board.

Correct.

Can I understand that as some form of ICSP port?

Yes, that's right. This is the SWD (serial wire debug) interface. It can be used both for programming (including burning the bootloader) the nRF52840 microcontroller and also doing debugging.

If so it doesnt seem to follow standard pinout for an ICSP port

That's correct. SWD is a similar concept, but it's not the same thing. Since it's a standardized interface, there is a lot of information available about SWD once you know the right keywords. The Arduino SAMD boards also have an SWD interface.

A bit lower are 2 components marked U4A and U4B, that I can´t associate at all. There is a comment next to it saying Crypto Auth.
Does someone know what kind of components those are and what their function is?

Those are the footprint for the ATECC508A crypto authentication chip. Note the "DNP" on the schematic. That stands for either "do not populate" or "do not place". This means that Arduino designed the circuit board so that the ATECC508A may be added, but intentionally didn't put that chip on the board during assembly. It just leaves the option for adding this capability to the board if needed.

[Loverboy7000]

awesome, thanks for the info pert. Very helpful!

Can you also recommend me a freeware PCB design tool that can open up the EAGLE files supplied with NANO 33 BLE and keeps the links between schematic, PCB layout and BOM intact?

The ones I found seem to struggle a bit and can´t really handle the whole project.

Andre

[pert]

The truth is, I've just been using Eagle to open Arduino's board design files. I'm using Eagle 7.7.0, which is the last one that doesn't require the online account. I know that some of Arduino's design files are not compatible with the latest Eagle versions (though it's easy to fix them), so you might be best off using Eagle 7 anyway.

I generally prefer Kicad, and I know the support for Eagle projects has been improving over time, but I haven't checked how the latest Kicad does with these files. Have you given Kicad a try?

I haven't done anything beyond giving a quick try to any EDA applications other than Kicad and Eagle, so I can't say whether there are other options. Maybe someone else here on the forum will be able to provide a better answer.