Let's start by breaking the '328 down into it's functional pieces. Then we'll look at each in turn.
Below is a block diagram of the '328 that identifies the major functional areas:
- the AVR Central Processing Unit CPU (red)
- memory: Flash, random access memory (RAM), and electrically erasable programmable read only memory (EEPROM) (orange)
- timers/counters (T/C 0, 1, and 2) (yellow)
- analog inputs (grey)
- digital I/O (megenta)
- serial I/O (green)
- SPI (cyan)
- I2C/TWI (blue)
- control and misc circuitry (white)
Let's walk through each section.
From the ATMega328 datasheet
