Nearly all AVRs have a 'serial' programming interface, that's what we'll be using to program them. If your chip requires SWD, JTAG or parallel, this software won't work!

In this example we'll show how to wire up an existing Arduino 328P compatible or raw 328P chip to a Feather M0 for programming

For other chips, the wiring is similar, but you'll need to look up which pins are Power, Ground, Reset, and SCK/MOSI/MISO

Power Pins

Do these pins first because they're easy to forget!

  • If connecting to a Arduino-compatible: connect GND on the Arduino to GND on the Feather. Then either plug the Arduino into USB, or connect the Arduino 5V to Feather USB
  • If connecting to a bare chip: connect both GND pins together and to the Feather GND. Connect AVCC to VCC to the Feather 3V pin
If you're breadboarding a bare ATMega328 chip, don't forget there are *two* power pins and *two* ground pins

Data Pins

  • Connect the CircuitPython SCK pin to the target SCK (on Uno/Atmega328 this is also known as Digital #13)
  • Connect the CircuitPython MISO pin to the target MISO (on Uno/Atmega328 this is also known as Digital #12)
  • Connect the CircuitPython MOSI pin to the target MOSI (on Uno/Atmega328 this is also known as Digital #11)
  • Connect CircuitPython D5 (or any digital pin, as long as you change the code too) to the target RESET

If you are breadboarding a chip, it may need a clock or crystal and it needs to be there to program the chip! If your board has a crystal or oscillator already, skip this. If you're programming a 'raw' ATmega328, you'll want to add it:

  • Connect CircuitPython D9 (or any digital pin with PWM out, as long as you change the code to) to the target XTAL1

Wiring Diagram for Raw ATMega328 Chip

  • VCC lines are Red
  • Ground/GND lines are Black
  • SCK is green
  • MOSI is blue
  • MISO is yellow
  • RESET is purple
  • XTAL is grey

Notice that the notch on the chip is to the right - away from the Feather!

Wiring for Arduino Compatible

For Arduino UNO and compatibles, we recommend powering from USB or DC power. Then connect GND pins together, and wire up Reset, SCK, MOSI, and MISO as seen above.

XTAL pin is not required, Arduinos have on-board crystals.

This guide was first published on Jan 11, 2018. It was last updated on Nov 25, 2023.

This page (Wiring) was last updated on Jan 07, 2018.

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