J-link EDU mini can't connect to nRF52840

[Kageni]

Hi a bit a noobie here, but I can't connect to my nRF52840 on my custom board that I made. I have tried both an ST-link V2 with openocd, flashing it into a black magic probe, and everything else I could think of. When that didn't work, I figured it would be easier wwith a J link, so I picked up a j-link edu mini from ada fruit and have been trying that. I have tried nrfjprog, J-link commander, and arduino and they all have not been able to connect to the target. I make a connection to the J link, it is only connecting to the target that fails. I tried to produce a log with nrfjprog --recover --log, but it either isn't producing a log file or I can't find it. I am using this nRF52840 module https://freqchina.en.alibaba.com/product/62501832603-810441729/bluetooth_5_0_module_mesh_module_zigbee_ANT_nRF52840_module_PTR9818.html. I have Swclk, swdio, vdd, and ground coming off the module into a 4 pin SWD connector, and connected those to my J-link via SWD.

[Kageni]

VTreg is getting 3.3V when measured between that and the ground pin.

[Jared]

Hi,

I don't have any experience with this module, nor can I prove that it's actually a real one. We have seen that people have bought non-legit from sites such as Alibaba and Ebay and then have connection issues.

Nevertheless,

Assuming that it's actually a real nRF inside:

For SWD to work you need to route out the:

• VCC
• SWDIO
• SWDCLK
• RESET(optional)

You also need to make sure that the nRF is supplied when you try to debug. It seems that you are supplying the nRF 3V3 via the debug interface, but I can't see where the supply is connected to the debugger?

regards

Jared 

[Kageni]

It is difficult to measure any of the DEC pins directly on the chip as they connect underneath the chip itself. I can access the reset pin on the module and it is reading 0V with negative point of volt meter on ground.

[Jared]

The reset pin is active low which means that if you measure 0V or lower than the nRF is held in a reset state. You need to check if anything is pulling the pin down externally.

[Kageni]

What should the voltage be measuring on the reset pin? It isn't grounded out as I don't measure continuity with ground on the reset pin unless the physical reset button is depressed. I have attached a picture of the pcb file which shows just a short lead from the reset button to the reset pin.

[Jared]

If the pin is used as a reset pin than an internal pull-up will be activated, so the pin should be logical high. Could you try pulling up the pin externally and see if you're able to connect to the device?

Also, how many samples are you seeing this issue on? What percentage?

[Kageni]

Hey I tried it on a different sample and it works! It seems like this was just a bad module. Thanks for your help!