Overview
The Leonardo ETH is a microcontroller board based on the ATmega32U4 (datasheet) and the new W5500 TCP/IP Embedded Ethernet Controller (datasheet). It has 20 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs) a 16 MHz crystal oscillator a RJ45 connection a micro USB connector a power jack an ICSP header and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started.
The Leonardo ETH differs from the preceding Ethernet board in that the ATmega32u4 has built-in USB communication eliminating the need for an external USB-to-serial converter. This allows the Leonardo ETH to appear to a connected computer as a mouse and keyboard in addition to a virtual (CDC) serial / COM port. It also has other implications for the behaviour of the board. Plus it has the new W5500 TCP/IP Embedded Ethernet Controller onboard.

Summary

• Microcontroller : ATmega32u4
• Operating Voltage : 5V
• Input Voltage Plug (recommended) : 7-12V
• Input Voltage Plug (limits) : 6-20V
• Input Voltage PoE (limits) : 36-57V
• Digital I/O Pins : 20
• PWM Channels : 7
• Arduino Pins reserved : 4 used for SD card select

10 used for W5500 select

• Analog Input Pins : 12
• DC Current per I/O Pin : 40 mA
• DC Current for 3.3V Pin : 1 A (only when powered via the external power supply)
• Flash Memory : 32 KB (ATmega32u4) of which 4 KB used by bootloader
• SRAM : 2.5 KB (ATmega32u4)
• EEPROM : 1 KB (ATmega32u4)
• Clock Speed : 16 MHz
• Micro SD card with active voltage translators

Power
VIN. The input voltage to the Arduino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin or if supplying voltage via the power jack access it through this pin.
5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V) the USB connector (5V) or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator and can damage your board. We don't advise it.
3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
GND. Ground pins.
IOREF. This pin on the Arduino board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the appropriate power source or enable voltage translators on the outputs for working with the 5V or 3.3V.
The optional PoE module is designed to extract power from a conventional twisted pair Category 5 Ethernet cable.

PoE module features are as follows:

• IEEE802.3af compliant
• Input voltage range 36V to 57V
• Overload and short-circuit protection
• 12V Output
• High efficiency DC/DC converter: typ 85% @ 80% load
• 1500V isolation (input to output)

Memory
The ATmega32u4 has 32 KB (with 4 KB used for the bootloader). It also has 2.5 KB of SRAM and 1 KB of EEPROM (which can be read and written with the EEPROM library).

Input and Output
Serial: 0 (RX) and 1 (TX): used to receive (RX) and transmit (TX) TTL serial data using the ATmega32U4 hardware serial capability. Note that on the Leonardo ETH the Serial class refers to USB (CDC) communication; for TTL serial on pins 0 and 1 use the Serial1 class.
TWI: 2 (SDA) and 3 (SCL): they support TWI communication using the Wire library.
External Interrupts: 3 (interrupt 0) 2 (interrupt 1) 0 (interrupt 2) 1 (interrupt 3) and 7 (interrupt 4). These pins can be configured to trigger an interrupt on a low value a rising or falling edge or a change in value. See the attachInterrupt() function for details.
PWM: 3 5 6 9 10 11 and 13. Provide 8-bit PWM output with the analogWrite() function.
SPI: on the ICSP header. These pins support SPI communication using the SPI library. Note that the SPI pins are not connected to any of the digital I/O pins as they are on the Uno They are only available on the ICSP connector. This means that if you have a shield that uses SPI but does NOT have a 6-pin ICSP connector that connects to the Leonardo's 6-pin ICSP header the shield will not work.
LED: 13. There is a built-in LED connected to the digital pin 13. When the pin is HIGH value the LED is on when the pin is LOW it's off.
Analog Inputs: A0-A5 A6 - A11 (on digital pins 4 6 8 9 10 and 12). The Leonardo has 12 analog inputs labeled A0 through A11 all of which can also be used as digital i/o. Pins A0-A5 appear in the same locations as on the Uno; inputs A6-A11 are on digital i/o pins 4 6 8 9 10 and 12 respectively. Each analog input provides 10 bits of resolution (i.e. 1024 different values). By default the analog inputs measure from ground to 5 volts though it is possible to change the upper end of their range using the AREF pin and the analogReference() function.
There are a couple of other pins on the board:
AREF. Reference voltage for the analog inputs. Used with analogReference().
Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset button to shields that block the one on the board.