Datasheet

6
ATmega325/3250/645/6450
2570K–AVR–04/07
Comparison between
ATmega325,
ATmega3250,
ATmega645 and
ATmega6450
The ATmega325, ATmega3250, ATmega645, and ATmega6450 differs only in memory
sizes, pin count and pinout. Table 1 on page 6 summarizes the different configurations
for the four devices.
Pin Descriptions The following section describes the I/O-pin special functions.
V
CC
Digital supply voltage.
GND Ground.
Port A (PA7..PA0) Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port A output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port A pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port A pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port B (PB7..PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port B output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port B pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port B has better driving capabilities than the other ports.
Port B also serves the functions of various special features of the
ATmega325/3250/645/6450 as listed on page 66.
Port C (PC7..PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port C output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port C pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port C pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port D (PD7..PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port D output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port D pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port D also serves the functions of various special features of the
ATmega325/3250/645/6450 as listed on page 69.
Port E (PE7..PE0) Port E is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port E output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port E pins that are externally pulled low will source
Table 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