General properties of AVR microcontrollers

This applies to all types of AVR microcontrollers because they all use same AVR core technology. So lets go through some of them:
• Ability to work at 1MIPS/MHz (MIPS – Millions Instructions Per Second);
• On chip Flash memory (now tiny series have up to 8kB, mega up to 256kB) with write cycle not less than 1000 times;
• On chip RAM memory (tiny series up to 512B, mega up to 8kB);
• On chip EEPROM memory (tiny series up to 512B, mega up to 4kB) with write cycle not less than 100000 times;
• Working frequencies up to 20MHz;
• Protection fuses from unintentional reading and modification of program and data memories;
• Ability to program in system – directly on board using ISP cable;
• Four types of clock generators: Internal generator, RC generator of clock cycles, Internal generator with external crystal resonator, and External synchronisation;
• Two or three power down modes;
• Some microcontroller can work at very low voltages like 1.8V

Other internal processor properties:
• Static architecture where minimal frequency equal to zero;
• ALU is connected directly to general purpose registers;
• Most of commands are performed in one clock cycle;
• Multilevel system of interrupts;
• Many sources of interrupts – two of them are external;
• Three level hardware stack.

I/O system properties:
• Software configurable and selection of I/O ports;
• Ports can be programmed as inputs and outputs independently to each other;
• Input buffers uses Smith triggers on all pins;
• Support of Internal Pull-Up resistors (about 35 to 120kOhm)

Peripheral devices vary from device to device. Refer to datasheets to find out what peripherals are included in concrete model. In general we can mention:
• 8 bit timer counter with pre-scaler;
• 16 bit timer counter with pre-scaler ;
• Watch dog timer;
• PWM generator;
• Analog comparator;
• ADC;
• Hardware modulator;
• SPI interface;
• TWI (I2C) interface;
• UART