The Atmega and Attiny series from Microchip (formerly Atmel) are 8-bit AVR microcontrollers widely used in embedded systems and the Arduino ecosystem. They are known for their simplicity, predictable behavior and strong community support.
This article provides a detailed technical overview of the most relevant AVR devices used in modern hobby and educational projects, including ATmega328P, ATmega2560, ATmega32U4, ATtiny85 and ATtiny88.
Architecture Overview
All devices in this family are based on the AVR 8-bit RISC architecture with a Harvard design (separate program and data memory).
- 8-bit CPU core
- Single-cycle execution (most instructions)
- Deterministic timing behavior
- Very low architectural complexity
This makes AVR microcontrollers particularly suitable for timing-critical and low-level control applications.
Clock Speed and Operating Voltage
Clock frequency depends on supply voltage and must follow datasheet limits.
- 16 MHz typical at 5V (Arduino Uno, Nano)
- 8 MHz typical at 3.3V (Pro Mini 3.3V, low-power boards)
- ATtiny devices often run at 1-8 MHz internal oscillator
- External crystal recommended for precise timing
Important: Running 16 MHz at 3.3V is outside official specifications, even if commonly done in hobby projects.
Memory Overview
- Flash: 4 KB to 256 KB
- SRAM: 256 bytes to 8 KB
- EEPROM: 256 bytes to 4 KB
Memory is limited compared to modern 32-bit MCUs and often the main constraint in larger projects.
GPIO and Electrical Characteristics
- Typical GPIO count: 6 to 86 pins depending on device
- Recommended current per pin: up to ~20 mA
- Absolute maximum per pin: 40 mA
- Total device current: typically up to ~200 mA (device/package dependent)
- 5V logic compatibility (major advantage)
Important: Absolute maximum ratings must not be used as operating values. For reliable designs, significantly lower currents should be used.
Analog Capabilities
- ADC resolution: 10-bit
- Channels: typically 4-16
- Internal voltage reference available
- No true DAC (PWM used instead)
Analog performance is suitable for sensors but not precision measurement.
Communication Interfaces
- UART: 1-4 (depending on device)
- I2C (TWI): 1 interface
- SPI: 1 interface
- USB: available on specific devices (ATmega32U4, ATmega16U2)
- No native CAN controller
ATtiny devices often have reduced or software-based interface implementations.
Timers and PWM
- Multiple 8-bit and 16-bit timers
- PWM outputs available on many pins
- Precise timing and signal generation possible
Toolchains and Ecosystem
- Arduino IDE (primary ecosystem)
- AVR-GCC
- PlatformIO
- Microchip Studio
Modern Arduino cores also support ATtiny devices, greatly expanding their usability.
Important Devices and Real-World Usage
ATmega328P
- Used in Arduino Uno, Nano, Pro Mini
- Most widely used AVR microcontroller
- Used in Arduino Mega
- Large number of GPIOs and UARTs
- Native USB support
- Used in Arduino Leonardo and Pro Micro
- Used as USB-to-UART bridge on Arduino Uno
ATtiny85
- Very small footprint (8-pin devices)
- ATtiny85 used in Digispark Kickstarter module
- Internal oscillator, limited I/O
- USB possible via software (V-USB)
- Larger ATtiny with more GPIO
- Closer to ATmega-class capabilities
- Supported by modern Arduino cores
Advantages
- Simple and predictable architecture
- Strong Arduino ecosystem
- 5V compatibility
- Low cost
- Excellent for small and embedded designs
Limitations
- Low performance
- Limited RAM
- No modern connectivity (WiFi, BLE, CAN)
- Limited scalability
Typical AVR Device Comparison
| Model | Flash | RAM | GPIO | UART | I2C | SPI | USB | Voltage | Package |
|---|---|---|---|---|---|---|---|---|---|
| ATmega328P | 32 KB | 2 KB | 23 | 1 | 1 | 1 | No | 1.8V / 3.3V / 5V* | DIP-28, TQFP-32 |
| ATmega2560 | 256 KB | 8 KB | 86 | 4 | 1 | 1 | No | 1.8V / 3.3V / 5V* | TQFP-100 |
| ATmega32U4 | 32 KB | 2.5 KB | 26 | 1 | 1 | 1 | Yes | 1.8V / 3.3V / 5V* | TQFP-44 |
| ATtiny85 | 8 KB | 512 B | 6 | 0 | 0 (USI) | 0 (USI) | No | 1.8V / 3.3V / 5V* | DIP-8, SOIC-8 |
| ATtiny88 | 8 KB | 1 KB | 28 | 1 | 1 | 1 | No | 1.8V / 3.3V / 5V* | TQFP-32 |
| ATmega16U2 | 16 KB | 512 B | 22 | 1 | 1 | 1 | Yes | 1.8V / 3.3V / 5V* | TQFP-32 |
*Maximum clock frequency depends on supply voltage according to datasheet.