Arduino Ports
The Arduino Uno has three I/O ports (B, C and D) that can be used for digital input and output. The bits in the ports are named on the Arduino board (and in Arduino’s own software tools) as D0 through D13 and A0 through A5. However these names are not the names that must be used when writing code to be compiled by the avr-gcc software for downloading to the Arduino.
The diagram below shows the relationship between the two sets of names.
