Board only shows up on my computer if the programmer is connected

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Hey all,


I am having an odd issue with my board, and I'd love to get input from the community. I have a custom board, but it is fairly similar to the Adafruit Grand Central M4 Express board. My board uses a SAMD51P19A. I've installed the Adafruit bootloader onto the board (found here:, and when I plug the board into my computer via USB, it shows up as a device as expected.


However, this is only true if and only if I leave my programmer attached to the board. I am using an Atmel ICE programmer with a Tag-Connect connector. As long as the programmer is plugged into my board, I am able to see the board show up as a USB device on my computer, but once I unplug the programmer from my board, then the board disappears as a USB device on my computer. The USB cable is still connected between the board and the computer, and the board is still receiving power (through the USB cable).


Pins PA25 and PA24 are USB Data+ and USB Data- respectively. Pins PA31, PA30, and PB30 are being used for programming the board (SWDIO, SWCLK, and SWO).


Any ideas on what could be causing such an issue? Thanks!

Last Edited: Tue. Aug 9, 2022 - 08:38 PM