What separates a mere microprocessor (such as the Z80, the 6502, the 8088, or even an Intel Pentium) from a microcontroller is the inclusion of all those other bits that are required for a complete computer circuit, including memory banks, clock circuits, and interface peripherals.
The AVR family of microcontrollers offers a wide variety of internal peripheral interfaces that make it easy to communicate with other devices. Let’s look at some of the major peripherals you can use.
General Purpose Input/Output (I/O)
The ATmega328 has three I/O ports: Port B, Port C, and Port D. The ATmega2560 has 11 I/O ports: Port A, Port B, Port C, Port D, Port E, Port F, Port G, Port H (they skipped Port I), Port J, Port K, and Port L.