Note: Some pins are not connected on a standard Arduino Uno R3 but still listed so you can use them if you had a custom board. It might also be possible that your ISP header of the 16u2 is flipped 180 ...

Once you’ve done that, you have essentially an Arduino with limited pinout and two onboard LEDs, ... On the other hand if you already have the Arduino, fetch the avr.isp.03 firmware and AVRdude.

Once you’ve done that, you have essentially an Arduino with limited pinout and two onboard LEDs, ... On the other hand if you already have the Arduino, fetch the avr.isp.03 firmware and AVRdude.