Rainbow Electronics ATmega8L - Manual (Page 5)

5
ATmega8
2486AS–08/01
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 on page 54.
Port C (PC6..PC0) / RESET Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port C 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 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 Table 15 on page 34. Shorter
pulses are not guaranteed to generate a reset.
The various special features of Port C are elaborated on page 57.
Port D (PD7..PD0) Port D is an 8-bit bidirectional 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 ATmega8 as listed on
page 59.
RESET Reset input. A low level on this pin for longer than the minimum pulse length will gener-
ate a reset, even if the clock is not running. The minimum pulse length is given in Table
15 on page 34. 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.
AVCC AVCC is the supply voltage pin for Port A and the A/D Converter. It should be externally
connected to V
CC
, even if the ADC is not used. If the ADC is used, it should be con-
nected to V
CC
through a low-pass filter.
AREF AREF is the analog reference pin for the A/D Converter.
ADC7..6 (TQFP and MLF
Package Only) In the TQFP and MLF package, ADC7..6 serve as analog inputs to the A/D converter.
These pins are powered from the analog supply and serve as 10-bit ADC channels.