What is the 'microcontroler' setting under 'networks?
The icon indicates its probably a serial device (i.e. a virtual com port). 

Normally you need to click the + sign below (your first screenshot), then select a interface, a default name will be presented (in your case Microcontroller). You could rename the service afterwards.

The problem is once the device is added its hard to see which port its connected to. Now if you goto the Terminal and type:

# list all h/w ports
networksetup -listallhardwareports

# list Services and their connected port
networksetup -listnetworkserviceorder


The last command should show you something like:

(1) Ethernet 1
(Hardware Port: Ethernet 1, Device: en0)

(2) Ethernet 2
(Hardware Port: Ethernet 2, Device: en1)

(x) Microcontroller
(Hardware Port: xxxx, Device: YYYY)


The device name (YYYY) you should find in your /etc folder (if connected).

So, if the device is connected you should find it in that /dev folder. You can check this by going to the terminal and type:

ls -l /dev | grep &lt;the name of the h/w port&gt;


If you then disconnect the device and they the command (above) again, and it disappears your sure.

To answer your question: how it works and how you set it up depends on what type of device it is. And its hard to say just based on this information.

Apparently this device got somehow added. As Ashely states, it could be a Raspberry PI, or some other USB device (with serial port).