Introduction to Arduino - Arduino Sketches: Tools and Techniques for Programming Wizardry - page 11

Figure 1-4: The Arduino Leonardo
Arduino Ethernet
The Arduino Ethernet, based on the ATmega328 found in the Uno, can connect to
an Ethernet network, a functionality needed in a number of projects. Physically,
the Arduino Ethernet has the same 14-digital inputs/outputs as the Arduino
Uno, with the exception that 4 are used to control the Ethernet module and on-
board micro-SD card reader, limiting the amount of pins available.
It is interesting to note that the Arduino Ethernet has an optional POE mod-
ule, short for Power Over Ethernet. This option enables the Arduino Ethernet
to be powered directly from an Ethernet connection, without the need for an
external power source provided that there is a POE supply on the other end of
the Ethernet cable. Without POE, the Arduino must be powered by an external
source
Another difference from other Arduino boards is the lack of a USB connector.
Because most of the space is taken up with an Ethernet connector, this device
instead supports a 6-pin serial programming header and is compatible with
numerous programming devices (including a device from Arduino, the USB-
Serial adapter). The Arduino Ethernet is shown in Figure 1-5.
Arduino Mega 2560
The Arduino Mega 2560 is only slightly larger than the Arduino Uno, but it has
more input and output pins. It has a total of 54 digital I/O pins and 16 analog