ATmega128
Port G (PG4..PG0)
Port G is a 5-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port G output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port G pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port G pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port G also serves the functions of various special features.
The port G pins are tri-stated when a reset condition becomes active, even if the clock is
not running.
In ATmega103 compatibility mode, these pins only serves as strobes signals to the
external memory as well as input to the 32 kHz Oscillator, and the pins are initialized to
PG0 = 1, PG1 = 1, and PG2 = 0 asynchronously when a reset condition becomes active,
even if the clock is not running. PG3 and PG4 are oscillator pins.
RESET
Reset input. A low level on this pin for longer than the minimum pulse length will gener-
ate a reset, even if the clock is not running. The minimum pulse length is given in Table
19 on page 50. Shorter pulses are not guaranteed to generate a reset.
XTAL1
XTAL2
AVCC
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
Output from the inverting Oscillator amplifier.
AVCC is the supply voltage pin for Port F and the A/D Converter. It should be externally
connected to VCC, even if the ADC is not used. If the ADC is used, it should be con-
nected to VCC through a low-pass filter.
AREF
PEN
AREF is the analog reference pin for the A/D Converter.
PEN is a programming enable pin for the SPI Serial Programming mode, and is inter-
nally pulled high . By holding this pin low during a Power-on Reset, the device will enter
the SPI Serial Programming mode. PEN has no function during normal operation.
Resources
A comprehensive set of development tools, application notes, and datasheets are avail-
able for download on http://www.atmel.com/avr.
7
2467OS–AVR–10/06
ATMEL [ ATMEL ]
