First of all: my board used to work fine.

Now my Nano 33 IoT turns ON (green light) when connected to USB on Mac but:

  1. doesn't enter in upload mode after pressing twice on board button.
  2. doesn't shows up in any serial port: nor /dev/cu.usbmodem14*01, neither /dev/tty.usbmodem14*01

For reasons too long to explain, I want to connect via ANY pins to the SAMD21 and force the burning of a new bootloader.

Is that possible in any way? Any idea is welcome!



1 Answer 1


Use the SWD interface and a programmer to burn the bootloader to SAMD.

enter image description here

source of the picture https://medium.com/@manuel.bl/arduino-in-circuit-debugging-with-platformio-9f699da57ddc

I had luck with Adafruit DAP library using an Arduino M0 to burn a bootloader to MKR Zero.

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