Pin Descriptions - Atmel ATmega48A Manual

1.1

Pin Descriptions

1.1.1 VCC
1.1.2 GND
1.1.3 Port B (PB7:0) XTAL1/XTAL2/TOSC1/TOSC2
1.1.4 Port C (PC5:0)
1.1.5 PC6/RESET
1.1.6 Port D (PD7:0)
8271D–AVR–05/11
ATmega48A/PA/88A/PA/168A/PA/328/P
Digital supply voltage.
Ground.
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). 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 when a reset condition becomes active,
even if the clock is not running.
Depending on the clock selection fuse settings, PB6 can be used as input to the inverting Oscil-
lator 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, PB7...6 is used as
TOSC2...1 input for the Asynchronous Timer/Counter2 if the AS2 bit in ASSR is set.
The various special features of Port B are elaborated in
84 and "System Clock and Clock Options" on page
Port C is a 7-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
PC5...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 when a reset condition becomes active,
even if the clock is not running.
If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note that the electrical char-
acteristics 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.
The minimum pulse length is given in
teed to generate a Reset.
The various special features of Port C are elaborated in
87.
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). 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 when a reset condition becomes active,
even if the clock is not running.
"Alternate Functions of Port B" on page
27.
Table 29-12 on page 324. Shorter pulses are not guaran-
"Alternate Functions of Port C" on page
3