nRF5340 Programming Issue

[LL01]

Hello everyone,

During the design of my core board, I encountered an issue where after flashing a demo program, the core board cannot be programmed again. The demo program I burned controls an LED to toggle every 1 second. I initially suspected a crystal oscillator problem, but after removing the 32MHz crystal, the waveform measured by the oscilloscope shows a frequency of 387Hz with a period of 2.58ms, confirming that the board is using the internal oscillator.

My core board is not powered externally—it only receives 3.3V power and GND through the debug pins. Currently, I cannot perform reprogramming, and even erase commands are ineffective, although I can still detect the nRF5340 chip. What could be the potential issue in this situation?

[Turbo J]

You need to have the reset line connected to the debugger in order to be able to "recover" the device. Picture looks like you missed that.

Most debuggers have the Vtarget line configured as voltage input by default in order to be able to accept a wide range of targets with different levels. 

[LL01]

Thank you for your suggestion. I just tried removing the pull-up resistor from the reset line and performed erase operations, but the MCU still did not respond. Then, I re-soldered the pull-up resistor and repeated the operations, yet the MCU remained unresponsive. All three circuit boards I have on hand are experiencing the same issue—they worked fine during the initial connection, allowing programming and operations, but subsequently stopped functioning.

[Turbo J]

If you bothered to read the product specifications, the "recovery" procedure has tight timing requirements on the reset line. Hence it needs to be connected to the debugger itself.

[LL01]

Thank you for the reminder. I did connect the reset wire to the debugging interface through soldering, but there was still no response.

[LL01]

Thank you all for your help. I finally determined that the issue was caused by setting the DCDC to a specific power mode, which prevented the board from operating normally. While the MCU was unable to respond, I shorted DCED to 3.3V and reconfigured the settings to resolve the problem. In future circuit designs, it will be modified to operate in DCDC mode.