Datasheet

5.2 Pin Descriptions
5.2.1 VCC
Digital supply voltage pin.
5.2.2 GND
Ground.
5.2.3 Port B (PB[7:0]) XTAL1/XTAL2/TOSC1/TOSC2
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each pin). 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 during a Reset condition even if the clock is not running.
Depending on the clock selection fuse settings, PB6 can be used as input to the inverting oscillator
amplifier and input to the internal clock operating circuit.
Depending on the clock selection fuse settings, PB7 can be used as output from the inverting oscillator
amplifier.
If the internal calibrated RC oscillator is used as chip clock source, PB[7:6] is used as TOSC[2:1] input for
the asynchronous timer/counter2 if the AS2 bit in ASSR is set.
5.2.4 Port C (PC[5:0])
Port C is a 7-bit bi-directional I/O port with internal pull-up resistors (selected for each pin). The PC[5:0]
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 during a Reset condition even if the clock is not running.
5.2.5 PC6/RESET
If the RSTDISBL fuse is programmed, PC6 is used as an I/O pin. Note that the electrical characteristics of
PC6 differ from those of the other pins of Port C.
If the RSTDISBL fuse is unprogrammed, PC6 is used as a 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. Shorter pulses are
not guaranteed to generate a Reset.
The various special features of Port C are elaborated in the Alternate Functions of Port C section.
5.2.6 Port D (PD[7:0])
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each pin). The Port D
output buffers 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 during a Reset condition even if the clock is not running.
5.2.7 AV
CC
AV
CC
is the supply voltage pin for the A/D Converter (ADC), PC[3:0], and PE[3:2]. It should be externally
connected 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. Note that PC[6:4] use digital supply voltage, V
CC
.
5.2.8 AREF
AREF is the analog reference pin for the A/D Converter.
ATmega48PA/88PA/168PA
Pin Configurations
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40002011A-page 20