Can I evaluate a board without SWDIO and SWDICLOCK?

[Anders012]

Hi, I'm developing a keyboard-pcb with NRF52840. I'm doing this as a hobby and are not that experienced with integrated circuits. Anyway, I designed and produced a pcb, but had not done my homework and read that I need to connect a debugger to SWDIO and SWDIOCLOCK. Theese pins are not availeble so I need to do some redesign.

My question is: Now that I have the pcb, I've checked that the VDD and VBUS are fine, what else can I test to ensure that I do not need to do a third pcb order?

Thanks to ketiljo  for my  last review https://devzone.nordicsemi.com/f/nordic-q-a/127758/help-evaluating-nrf52840-schematic/564850bakenko_65_iso_schematic.pdfbakenko_65_iso_pcb.pdf

[Szabolcs]

Hi Anders,

the nRF circuitry looks fine, Ketil has already checked, but I just double checked too. I am, however, a bit confused about the circuit below:

What is this supposed to do? If the USB is disconnected, I don't see any way how the battery would power the device. Looks like the pins are swapped, and the VBUS should be on the gate, to switch the battery? Or perhaps you wanted to use the MOSFET in an ideal-diode arrangement?

Regarding the nRF, I think it should be still possible to program it using the built-in USB DFU firmware, as described here, so give that a try. Alternatively, you can try to remove the chip with a hot-air gun, and replace it with a pre-programmed one (e.g. from another board that has a debug connector). You could also try to connect thin copper wires to these pads before putting the chip back on to access the SWD. (This is a bit difficult task, but possible.)

Otherwise, if the nRF cannot be programmed, there is not much else to test. If the VIN, +3V3 and VBUS pins all have the right voltage, the MCU should function properly. (You should test the voltages in all configurations, with power from battery, USB, and both at the same time.)

[Anders012]

Thank you for the reply, the battery circuit is mostly copied from seeedstudio xiao nrf52840 https://files.seeedstudio.com/wiki/XIAO-BLE/Seeed-Studio-XIAO-nRF52840-Sense-v1.1.pdf . It does look like I've swapped the 2/3 pins when I changed some components.

Thank you for the feedback, I will first try the DFU over a serial USB connection before trying to swap chips with a hot air gun. I only have an "industrial" type, and I think it would be hard to not overheat the pcb since it is not intended for soldering.