This page describes which data pins on the arduino are connected to which internal ports on the ATMega.
Digital pins 0-7 are on port D, pins 0-7. Use PORTD, and PORTD[0-7] to refer to the port in code. DDRD is the port direction register, and DDD[0-7] are the pin direction bits.
Digital pins 8-13 are on port B, pins 0-5. Use PORTB, PORTB[0-5], DDRB and DDB[0-5].
Analog pins 0-5 are on port C, pins 0-5. The arduino
API sets these up as analog inputs, but they can also be used as digital inputs or outputs.
