I desgined a PCB based on the nRF52840 module and led out the SWDIO and SWDCLK pins to Micro USB.
I used jlink v9 and connected three pins in SWD download mode. The SWDIO and SWDCLK and the GND pins are connected to USB Micro port. The nRF52840 module also gets a stable 3.3V power supply, but I found that Jlink cannot recognize the firmware of the nRF52840 in keil.
I tried to use a flying lead to connect directly to the pins of the nRF52840 module nad connect the three pins SWDIO,SWDCLK and GND. At this time. Jlink can recognize the firmware and download the program successfully.
So I guess if the download cable is too long to maintain a stable connection. I tried to reduce the length of the download cable but it didn't work. Like as long as it is connected through my PCB, the firmware cannot be recognized. It is also measured between the pins with a multimeter is a stable connection, how can I shorten the length of the download cable or reduce the recognition frequency in keil cannot solve the problem.
So all the phenomena point to the result, that is, there is a problem with the desgin od my PCB. I can't figure out why the direct fly line can be downloaded, but the recognition failed after passing through the Micro USB port connection on my PCB, so if anyone who can help me check my PCB desgin and find the cause of the problem? My PCB desgin is attached below.
ps: I used the core nRF52840 module of WaveShare.
