6
2570N–AVR–05/11
ATmega325/3250/645/6450
2.2
Comparison between ATmega325, ATmega3250, ATmega645 and ATmega6450
The ATmega325, ATmega3250, ATmega645, and ATmega6450 differ only in memory sizes, pin
devices.
2.3
Pin Descriptions
The following section describes the I/O-pin special functions.
2.3.1
V
CC
Digital supply voltage.
2.3.2
GND
Ground.
2.3.3
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.
2.3.4
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.
Po rt B al so se rve s t h e f u nct i o n s of va ri ou s spe c ial f e a t ur es of t h e At me l
ATmega325/3250/645/6450 as listed on
page 68.2.3.5
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.
Table 2-1.
Configuration Summary
Device
Flash
EEPROM
RAM
General Purpose
I/O Pins
ATmega325
32Kbytes
1Kbytes
2Kbytes
54
ATmega3250
32Kbytes
1Kbytes
2Kbytes
69
ATmega645
64Kbytes
2Kbytes
4Kbytes
54
ATmega6450
64Kbytes
2Kbytes
4Kbytes
69