5

2570L–AVR–08/07

ATmega325/3250/645/6450

The ATmega325/3250/645/6450 provides the following features: 32/64K bytes of In-System

Programmable Flash with Read-While-Write capabilities, 1/2K bytes EEPROM, 2/4K byte

SRAM, 54/69 general purpose I/O lines, 32 general purpose working registers, a JTAG interface

for Boundary-scan, On-chip Debugging support and programming, three flexible Timer/Counters

with compare modes, internal and external interrupts, a serial programmable USART, Universal

Serial Interface with Start Condition Detector, an 8-channel, 10-bit ADC, a programmable

Watchdog Timer with internal Oscillator, an SPI serial port, and five software selectable power

saving modes. The Idle mode stops the CPU while allowing the SRAM, Timer/Counters, SPI

port, and interrupt system to continue functioning. The Power-down mode saves the register

contents but freezes the Oscillator, disabling all other chip functions until the next interrupt or

hardware reset. In Power-save mode, the asynchronous timer will continue to run, allowing the

user to maintain a timer base while the rest of the device is sleeping. The ADC Noise Reduction

mode stops the CPU and all I/O modules except asynchronous timer and ADC to minimize

switching noise during ADC conversions. In Standby mode, the crystal/resonator Oscillator is

running while the rest of the device is sleeping. This allows very fast start-up combined with low-

power consumption.

The device is manufactured using Atmel’s high density non-volatile memory technology. The

On-chip In-System re-Programmable (ISP) Flash allows the program memory to be repro-

grammed In-System through an SPI serial interface, by a conventional non-volatile memory

programmer, or by an On-chip Boot program running on the AVR core. The Boot program can

use any interface to download the application program in the Application Flash memory. Soft-

ware in the Boot Flash section will continue to run while the Application Flash section is updated,

providing true Read-While-Write operation. By combining an 8-bit RISC CPU with In-System

Self-Programmable Flash on a monolithic chip, the Atmel ATmega325/3250/645/6450 is a pow-

erful microcontroller that provides a highly flexible and cost effective solution to many embedded

control applications.

The ATmega325/3250/645/6450 AVR is supported with a full suite of program and system

development tools including: C Compilers, Macro Assemblers, Program Debugger/Simulators,

In-Circuit Emulators, and Evaluation kits.

3.2

Comparison between ATmega325, ATmega3250, ATmega645 and ATmega6450

The ATmega325, ATmega3250, ATmega645, and ATmega6450 differs only in memory sizes,

pin count and pinout. Table 3-1 on page 5 summarizes the different configurations for the four

devices.

3.3

Pin Descriptions

The following section describes the I/O-pin special functions.

Table 3-1.

Configuration Summary

Device

Flash

EEPROM

RAM

General Purpose

I/O Pins

ATmega325

32K bytes

1K bytes

2K bytes

54

ATmega3250

32K bytes

1K bytes

2K bytes

69

ATmega645

64K bytes

2K bytes

4K bytes

54

ATmega6450

64K bytes

2K bytes

4K bytes

69