5
ATmega161(L)
1228C–AVR–08/02
Pin Descriptions
VCC Supply voltage.
GND Ground.
Port A (PA7..PA0) Port A is an 8-bit bi-directional I/O port. Port pins can provide internal pull-up resistors
(selected for each bit). The Port A output buffers can sink 20 mA and can drive LED dis-
plays directly. When pins PA0 to PA7 are used as inputs and are externally pulled low,
they will source current if the internal 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 serves as a Multiplexed Address/Data port when using external memory
interface.
Port B (PB7..PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port B output
buffers can sink 20 mA. 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 ATmega161 as listed
on page 92.
Port C (PC7..PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port C output
buffers can sink 20 mA. 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 as an address high output when using external memory interface.
Port D (PD7..PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port D output
buffers can sink 20 mA. 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 ATmega161 as listed
on page 101.
Port E (PE2..PE0) Port E is a 3-bit bi-directional I/O port with internal pull-up resistors. The Port E output
buffers can sink 20 mA. As inputs, Port E pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port E pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port E also serves the functions of various special features of the ATmega161 as listed
on page 107.
RESET
Reset input. A low level on this pin for more than 500 ns will generate a Reset, even if
the clock is not running. Shorter pulses are not guaranteed to generate a Reset.
XTAL1 Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
XTAL2 Output from the inverting Oscillator amplifier.
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