Overview
The ATmega644 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the ATmega644 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.

FEATUREs
• High-performance, Low-power Atmel® AVR® 8-bit Microcontroller
• Advanced RISC Architecture
   – 131 Powerful Instructions – Most Single-clock Cycle Execution
   – 32 × 8 General Purpose Working Registers
   – Fully Static Operation
   – Up to 20 MIPS Throughput at 20MHz
• High Endurance Non-volatile Memory segments
   – 64 Kbytes of In-System Self-programmable Flash program memory
   – 2 Kbytes EEPROM
   – 4 Kbytes Internal SRAM
   – Write/Erase cyles: 10,000 Flash/100,000 EEPROM(1)(3)
   – Data retention: 20 years at 85°C/100 years at 25°C(2)(3)
   – Optional Boot Code Section with Independent Lock Bits
   In-System Programming by On-chip Boot Program
   True Read-While-Write Operation
   – Programming Lock for Software Security
• JTAG (IEEE std. 1149.1 Compliant) Interface
   – Boundary-scan Capabilities According to the JTAG Standard
   – Extensive On-chip Debug Support
   – Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
• Peripheral Features
   – Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes
   – One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture Mode
   – Real Time Counter with Separate Oscillator
   – Six PWM Channels
   – 8-channel, 10-bit ADC
   Differential mode with selectable gain at 1x, 10x or 200x
   – Byte-oriented Two-wire Serial Interface
   – One Programmable Serial USART
   – Master/Slave SPI Serial Interface
   – Programmable Watchdog Timer with Separate On-chip Oscillator
   – On-chip Analog Comparator
   – Interrupt and Wake-up on Pin Change
• Special Microcontroller Features
   – Power-on Reset and Programmable Brown-out Detection
   – Internal Calibrated RC Oscillator
   – External and Internal Interrupt Sources
   – Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby and Extended Standby
• I/O and Packages
   – 32 Programmable I/O Lines
   – 40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF
• Speed Grades
   – ATmega644V: 0 - 4MHz @ 1.8V - 5.5V, 0 - 10MHz @ 2.7V - 5.5V
   – ATmega644: 0 - 10MHz @ 2.7V - 5.5V, 0 - 20MHz @ 4.5V - 5.5V
• Power Consumption at MHz, 3V, 25⋅C
   – Active: 240µA @ 1.8V, 1MHz
   – Power-down Mode: 0.1µA @ 1.8V