Datasheet

more than 12V, the voltage regulator may overheat and damage the board. The recommended
range is 7 to 12 volts.
The power pins are as follows:
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. The regulated power supply used to power the microcontroller and other components on
the board. This can come either from VIN via an on-board regulator, or be supplied by USB
or another regulated 5V supply.
3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50
mA.
GND. Ground pins.
IOREF. The voltage at which the i/o pins of the board are operating (i.e. VCC for the board).
This is 5V on the Leonardo.
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).
Each of the 20 digital i/o pins on the Leonardo can be used as an input or output, using
pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can
provide or receive a maximum of 40 mA and has an internal pull-up resistor (disconnected
by default) of 20-50 kOhms. In addition, some pins have specialized functions:
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, 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). Support TWI communication using the Wire library.
External Interrupts: 2 and 3. 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 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 provide 10 bits of resolution (i.e. 1024
different values). By default the analog inputs measure from ground to 5 volts, though is it
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().