2.3.5 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 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.
Port D also serves the functions of various special features of the Atmel® ATmega16/32/64/M1/C1 as listed on 64.
2.3.6 Port E (PE2..0) RESET/ XTAL1/ XTAL2
Port E is an 3-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The port E output buffers have
symmetrical drive characteristics with both high sink and source capability. 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.
If the RSTDISBL fuse is programmed, PE0 is used as an I/O pin. Note that the electrical characteristics of PE0 differ from
those of the other pins of Port E.
If the RSTDISBL fuse is unprogrammed, PE0 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 Table 7-1 on page
39. Shorter pulses are not guaranteed to generate a reset.
Depending on the clock selection fuse settings, PE1 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, PE2 can be used as output from the inverting oscillator amplifier.
The various special features of Port E are elaborated in Section 9.3.5 “Alternate Functions of Port E” on page 67 and Section
5.1 “Clock Systems and their Distribution” on page 25.
2.3.7 AVCC
AVCC is the supply voltage pin for the A/D converter, D/A converter, current source. It should be externally connected to
VCC, even if the ADC, DAC are not used. If the ADC is used, it should be connected to VCC through a low-pass filter (see
Section 18.6.2 “Analog Noise Canceling Techniques” on page 204).
2.3.8 AREF
This is the analog reference pin for the A/D converter.
2.4
About Code Examples
This documentation contains simple code examples that briefly show how to use various parts of the device. These code
examples assume that the part specific header file is included before compilation. Be aware that not all C compiler vendors
include bit definitions in the header files and interrupt handling in C is compiler dependent. Please confirm with the C
compiler documentation for more details.
10
ATmega16/32/64/M1/C1 [DATASHEET]
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
