19 PB5 Digital Pin This pin act as a master clock output and slave clock input for SPI.

18 PB4 Digital Pin This pin act as a master clock input and slave clock output. 17 PB3 Digital Pin (PWM) This pin is used as a master data output and slave data input for the SPI interface. 16 PB2 Digital Pin (PWM) This pin acts as a slave choice i/p. 8 GND Ground The Ground of the system 9 XTAL Crystal Oscillator This pin should be connected to one pin of the crystal oscillator to provide an external clock pulse to the chip 10 XTAL Crystal Oscillator This pin should also be connected to the other pin of the crystal oscillator to provide an external clock pulse to the chip 11 PD5 Digital Pin (PWM) Pin 11 is used for external counter source Timer1 12 PD6 Digital Pin (PWM) Positive Analog Comparator i/ps 13 PD7 Digital Pin Negative Analog Comparator i/ps 14 PB0 Digital Pin Counter or Timer input source pin 15 PB1 Digital Pin (PWM) Counter or Timer compare match A. 2 PD0 Digital Pin (RX) This is the input pin for serial communication 3 PD1 Digital Pin (TX) This is the output pin for serial communication 4 PD2 Digital Pin It is used as an external interrupt 0 5 PD3 Digital Pin (PWM) It is used as an external interrupt 1 6 PD4 Digital Pin It is used for external counter source Timer0 7 Vcc Positive Voltage Positive supply of the system. Pin Name Pin Function Pin Function Description 1 PC6 Reset This pin helps to reset the microcontroller.

Atmel arduino uno datasheet