This is the first time that I realized that extra SMD IC near the USB port of the Arduino UNO is actually a fully fledged microcontroller, I thought that it was just a USB to Serial converter. Further research into this chip left me with more questions than answers.

First of all, why did Arduino decide to use the Atmega16U2 as a USB to Serial converter? Couldn't they have gone with an FTDI chip instead? I came across this phrase on Quora "The best part is that you can also program and create your own applications on the 16u2 if you have an In-circuit Serial Programmer". How exactly does this work?

What about the two other set of connectors on the board? (other than the two main rows of headers) The ones labeled ICSP and JP2? Is the JP2 for the 16U2? I read that these could be used for burning the code onto the Atmega328P so that it can be modified, but not overwritten. What are any other uses for the 16U2 on the Arduino UNO?

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  • FTDI is more expensive than the 16U2 AFAIK. Examples of reprogramming it are: to use it as a USB MIDI device or HID. – Wesley Lee Jan 25 at 12:45
  • @Wesley Lee How do you actually reprogram it though? – skillz21 Jan 25 at 12:46
  • There is a separate ISP/ICSP header for it. Then use something like an Arduino as ISP, Atmel ICE, etc (I have no time now, but I might bbe able to write an answer and post photos soon) – Wesley Lee Jan 25 at 12:48

First reason I'd guess is price:

They can probably get much better deals considering that the Atmega328 is also from Atmel (now Microchip).

About the programming:

There are some projects which make the Atmega16U2 into a MIDI device over USB or HID, for example some repos: 1, 2, 3. I've used the second one I think, and it works fine.

You can program it with an ISP/ICSP programmer such as Atmel ICE(below) or Arduino ISP.

enter image description here

Use the ISP pins by the Atmega16U2:

enter image description here

  • 1
    "They can probably get much better deals" -- I wouldn't be surprised if part of this decision was that Atmel offered the Arduino team a sweetheart deal on that part. – duskwuff Jan 26 at 0:18
  • @duskwuff -- True, it could have been the other way around! – Wesley Lee Jan 26 at 0:21

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