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    I/O - All 54 digital bins on the Arduino 2560 can either be used as an input or an output, using pinMode(), digitalWrite(), and digitalRead() functions.  They operate at 5 volts and each pin can provide and receive a maximum of 40 mA and has an internal pull-up resistor (that is disconnected by default) of 20-50 kOhms.

    The following pins have specialized functions:

    Serial: 0 (RX) and 1 (TX) *

    Serial 1: 19 (RX and 18 (TX)

    Serial 2: 17 (RX) and 16 (TX)

    Serial 3: 15 (RX) and 14 (TX)

    * Also connected to the corresponding pins of the ATmega16U2 USB-to-TTL Serial chip.

    External Interrupts: Pins 2 (interrupt 0), 3 (interrupt 1), 18 (interrupt 5), 19 (interrupt 4), 20 (interrupt 3), and 21 (interrupt 2) can be configured to trigger an interrupt on a low value, a rising or falling edge, or a change in value.

    PWM: Pins 2 to 13 and 44 to 46 provide 8-bit PWM output with the analogWrite() function.

    SPI: Pins 50 (MISO), 51 (MOSI), 52 (SCK), 53 (SS) support SPI communication using the SPI library.  They are also broken out on the ICSP header, which is compatible with the Uno, Duemilanove, and Diecimilia.

    LED: Pin 13 connects to the built-in LED. When the pis is HIGH value the LED is on, when it is LOW value it's off.

    TWI: Pin 20 (SDA) and 21 (SCL) support TWI communication using the WIRE library.

    AREF: The reference voltage for analog inputs is used with analogReference().

    Reset: for this pin bring the reset line LOW to reset the microcontroller.  This pin is typically used when there is a shield that is blocking the reset on the board.


    Atmega2560 Pin Mapping