ATMEGA644 datasheet(18/374 Pages) ATMEL

18 / 374 page

2593L–AVR–02/07

ATmega644

AVR Memories

This section describes the different memories in the ATmega644. The AVR architecture has two

main memory spaces, the Data Memory and the Program Memory space. In addition, the

ATmega644 features an EEPROM Memory for data storage. All three memory spaces are linear

and regular.

6.1

In-System Reprogrammable Flash Program Memory

The ATmega644 contains 64K bytes On-chip In-System Reprogrammable Flash memory for

program storage. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized as

32/64 x 16. For software security, the Flash Program memory space is divided into two sections,

Boot Program section and Application Program section.

The Flash memory has an endurance of at least 10,000 write/erase cycles. The ATmega644

Program Counter (PC) is 15/16 bits wide, thus addressing the 32/64K program memory loca-

tions. The operation of Boot Program section and associated Boot Lock bits for software

protection are described in detail in ”Memory Programming” on page 283. ”Memory Program-

ming” on page 283 contains a detailed description on Flash data serial downloading using the

SPI pins or the JTAG interface.

Constant tables can be allocated within the entire program memory address space (see the LPM

– Load Program Memory instruction description.

Timing diagrams for instruction fetch and execution are presented in ”Instruction Execution Tim-

ing” on page 14.

ATMEGA644 Datasheet(PDF) 18 Page - ATMEL Corporation