ATmega128A
JTAG interface is enabled, the pull-up resistors on pins PF7(TDI), PF5(TMS), and PF4(TCK) will
be activated even if a Reset occurs.
The TDO pin is tri-stated unless TAP states that shift out data are entered.
Port F also serves the functions of the JTAG interface.
In ATmega103 compatibility mode, Port F is an input Port only.
2.3.9
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.
2.3.10
RESET
Reset input. A low level on this pin for longer than the minimum pulse length will generate a
reset, even if the clock is not running. The minimum pulse length is given in
“System and Reset
Characteristics” on page 324.
Shorter pulses are not guaranteed to generate a reset.
2.3.11
XTAL1
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
2.3.12
XTAL2
Output from the inverting Oscillator amplifier.
2.3.13
AVCC
AVCC is the supply voltage pin for Port F and the A/D Converter. It should be externally con-
nected to V
CC
, even if the ADC is not used. If the ADC is used, it should be connected to V
CC
through a low-pass filter.
2.3.14
AREF
AREF is the analog reference pin for the A/D Converter.
2.3.15
PEN
PEN is a programming enable pin for the SPI Serial Programming mode, and is internally pulled
high . By holding this pin low during a Power-on Reset, the device will enter the SPI Serial Pro-
gramming mode. PEN has no function during normal operation.
19
8151GS–AVR–07/10
ATMEL [ ATMEL CORPORATION ]
