• Boot Loader capabilities is not supported.
• It is not possible to adjust the frequency of the internal calibrated RC Oscillator.
• The External Memory Interface can not release any Address pins for general I/O, neither configure different wait
states to different External Memory Address sections.
• Only EXTRF and PORF exist in the MCUCSR Register.
• No timed sequence is required for Watchdog Timeout change.
• Only low-level external interrupts can be used on four of the eight External Interrupt sources.
• Port C is output only.
• USART has no FIFO buffer, so Data OverRun comes earlier.
• The user must have set unused I/O bits to 0 in ATmega103 programs.
2.3
2.3.1
Pin Descriptions
VCC
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 buf-
fers 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 A also serves the functions of various special features of the ATmega64A as listed on
page 72.
2.3.2
2.3.3
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 buf-
fers 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 also serves the functions of various special features of the ATmega64A as listed on
page 73.
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 buf-
fers 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 C also serves the functions of special features of the ATmega64A as listed on
page 76.
In ATmega103 com-
patibility mode, Port C is output only, and the port C pins are
not
tri-stated when a reset condition becomes active.
2.3.6
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 buf-
fers 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 ATmega64A as listed on
page 77.
ATmega64A [DATASHEET]
8160DS–AVR–02/2013
5
ATMEL [ ATMEL CORPORATION ]
