Introduction
The ATmega808/809/1608/1609 microcontrollers are part of the megaAVR® 0-series, which uses the AVR® processor with hardware multiplier running at up to 20 MHz, and offers a wide range of Flash sizes up to 48 KB, up to 6 KB of SRAM, and 256 bytes of EEPROM in 28-, 32-, 40-, or 48-pin packages. The series uses the latest technologies from Microchip with a flexible and low-power architecture, including Event System and SleepWalking, accurate analog features, and advanced peripherals.
The devices described in this data sheet offer 8 or 16 KB in a 28/32/48-pin package.

megaAVR® 0-series Overview
The figure below shows the megaAVR® 0-series devices, laying out pin count variants and memory sizes:
• Vertical migration is possible without code modification, as these devices are fully pin and feature compatible
• Horizontal migration to the left reduces the pin count and, therefore, the available features

FEATUREs
• AVR® CPU:
   – Single-cycle I/O access
   – Two-level interrupt controller
   – Two-cycle hardware multiplier
• Memories:
   – 8 or 16 KB In-system self-programmable Flash memory
   – 256B EEPROM
   – 2 KB SRAM
   – Write/Erase endurance:
      • Flash 10,000 cycles
      • EEPROM 100,000 cycles
   – Data retention: 40 years at 55°C
• System:
   – Power-on Reset (POR) circuit
   – Brown-out Detector (BOD)
   – Clock options:
      • 16/20 MHz low-power internal oscillator
      • 32.768 kHz Ultra Low-Power (ULP) internal oscillator
      • 32.768 kHz external crystal oscillator
      • External clock input
   – Single-pin Unified Program Debug Interface (UPDI)
   – Three sleep modes:
      • Idle with all peripherals running for immediate wake-up
      • Standby
         – Configurable operation of selected peripherals
         – SleepWalking peripherals
      • Power-Down with limited wake-up functionality
• Peripherals:
   – One 16-bit Timer/Counter type A (TCA) with a dedicated period register and three compare channels
   – Up to four 16-bit Timer/Counters type B (TCB) with input capture
   – One 16-bit Real-Time Counter (RTC) running from an external crystal or an internal RC oscillator
   – Up to four USARTs with fractional baud rate generator, auto-baud, and start-of-frame detection
   – Host/client Serial Peripheral Interface (SPI)
   – Host/client TWI with dual address match
      • Can operate simultaneously as host and client
      • Standard mode (Sm, 100 kHz)
      • Fast mode (Fm, 400 kHz)
      • Fast mode plus (Fm+, 1 MHz)
   – Event System for core independent and predictable inter-peripheral signaling
   – Configurable Custom Logic (CCL) with up to four programmable Look-up Tables (LUT)
   – One Analog Comparator (AC) with a scalable reference input
   – One 10-bit 150 ksps Analog-to-Digital Converter (ADC)
   – Five selectable internal voltage references: 0.55V, 1.1V, 1.5V, 2.5V, and 4.3V
   – CRC code memory scan hardware
      • Optional automatic CRC scan before code execution is allowed
   – Watchdog Timer (WDT) with Window mode, with a separate on-chip oscillator
   – External interrupt on all general purpose pins
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