Argon 2 Not Booting in Known Good Board

Hi - I am using a 3rd party board w/an Argon device plugged into a feather socket. The board originally shipped with a HUZZAH32 and the Argon replaces it without modification. I am trying to replace Argon w/a new Photon 2 and the board will not boot, at all. Photon boots and runs the firmware as expected when not plugged into the board socket. When I plug the board into the socket it does not enter any of the boot sequences - the blue light showing power illuminates but the status LED does not ever light up.

The board layout is below. As best as I can tell the only difference, based on the migration guide from Argon to Photon2, is a note on the SCL and SDA - "SCL. Use Wire object. Use 1.5K to 10K external pull-up resistor." that does not exist in the current board design. Question to the community, would this cause the board boot problem I've described? If so, aside from modifying the board, is there any workaround?

I2C is almost certainly not the reason the Photon 2 won't boot.

Is that schematic complete, or is it more like a block diagram?

If there is a pull-down on GPIO12 pH_EN, that is why the Photon 2 won't boot. Same for TX, but that looks to be unconnected.

GPIO12 is Particle pin D7. If you pull D7 low when the P2 or Photon 2 is booting, the MCU will go into MCU test mode. Since this is a low-level hardware feature that occurs before the bootloader is run, there is no way to turn it off. That's why the Particle status LED does not come on.

If you can leave D7 unconnected or pull to 3V3, the Photon 2 will boot normally. Also beware of using D7 as an output to control an external circuit. Because D7 is also SWDIO it will be pulled high when the bootloader is run for SWD/JTAG. You can use it as GPIO later, but note that it will always go high at boot briefly.

See boot mode pins.


I believe the problem is D7 is pulled low w/the board, which based on what you outlined would put the board in test mode. Bummer, the board is not configurable. Is there another Particle board similar to the way Argon works and won't bump into this pin (or the other _EN pins)?

There is no other Wi-Fi board, but the Boron cellular device is pin-compatible with the Argon, has the same nRF52840 MCU, does not have restrictions on D7 or RX, and does not have SWD on D6/D7.

Also we still have ARGNKIT and ARGNTRAY50 available at this time.