Flashing the firmware

There is an automated job that compiles the firmware, check out releases. You'll need the .hex file. You can compile yourself, of course.

To flash the firmware, I use an ATMEL-ICE, sourceable from Mouser/DigiKey/etc. (~$100).

A much cheaper alternative is Adafruit High Voltage UPDI Friend - USB Serial UPDI Programmer (~$10).

Hardware

There are test points on the bottom of the transponder:

• VDD powers the LDO, apply 4+ V here
• VTG is a testpoint to check the LDO output voltage (should be 3.3V)
• GND
• UPDI is the programming pin

You can connect +3.3V directly to VTG, as the LDO has reverse current protection, and not use VDD (leave floating).

The v2 transponder's test point spacing is 2.54 mm / 0.1" away from each other. You need pogo pins to make proper contact. Adafruit, AliExpress.

Software

I use avrdude, the makescript use it as well.

Program both the fuses and the flash memory! The fuses are set to use the 20 MHz internal RC oscillator as a fallback if the crystal oscillator fails, as a fallback mechanism.

This does both:

make flash

OR:

avrdude -c serialupdi -p attiny816 -U "flash:w:main.hex" -U fuse1:w:0x02:m