In addition to the 32U4 chip, the Yún has an additional processor, an Atheros AR9331, which
runs a distribution of Linux for embedded systems named Linino, based on OpenWrt. A full
install of Python 2.7 is included as well.
The Yún has a number of different physical characteristics and connectors than the Leonardo.
There is an on-board SD slot, Ethernet jack, and a USB-A Host connector. There is no power
barrel connector on the Yún; it can be powered from the micro-USB connector.
There is no built in 5V regulator. If you power your Yún with more than 5V, you will likely
damage it. If you are not powering the Yún from the micro-USB connection, you can apply
power to the Vin and 5V pins on the board. It is recommended to power the Yún from the USB
connection whenever possible.
The SD, Ethernet, and USB-A connectors are not physically connected to the 32U4 processor,
they are connected to the AR9331.
The Yún's 32U4 functions in the same way as the Leonardo, except you cannot use
Serial1
. It
is reserved for communication with the AR9331 processor.
The Yún also has a WiFi module built on board, allowing it to connect to a wireless router, or act
as an access point.
The 32u4, WiFi, and AR9331 processors all have their own reset buttons.
