Datasheet

3V. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
⏚ Ground pins.
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 Micro 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 Micro, 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: 0(RX), 1(TX), 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
Arduino Uno, they are only available on the ICSP connector and on the nearby pins labelled
MISO, MOSI and SCK.
RX_LED/SS This is an additional pin with respect to the Leonardo. It is connected to the
RX_LED that indicates the activity of transmission during USB communication, but is can
also used as slave select pin (SS) in SPI communication.
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 Micro
has a total of 12 analog inputs, pins from A0 to A5 are labelled directly on the pins and the
other ones that you can access in code using the constants from A6 trough A11 are shared
respectively on digital pins 4, 6, 8, 9, 10, and 12. All of which can also be used as digital I/O.
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().
Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset button
to shields which block the one on the board.