ATMEGA8A View Datasheet(PDF) - Atmel Corporation
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ATMEGA8A Datasheet PDF : 13 Pages
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The Atmel®AVR® AVR core combines a rich instruction set with 32 general purpose working registers. All the 32
registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be
accessed in one single instruction executed in one clock cycle. The resulting architecture is more code efficient
while achieving throughputs up to ten times faster than conventional CISC microcontrollers.
The ATmega8A provides the following features: 8K bytes of In-System Programmable Flash with Read-While-
Write capabilities, 512 bytes of EEPROM, 1K byte of SRAM, 23 general purpose I/O lines, 32 general purpose
working registers, three flexible Timer/Counters with compare modes, internal and external interrupts, a serial pro-
grammable USART, a byte oriented Two-wire Serial Interface, a 6-channel ADC (eight channels in TQFP and
QFN/MLF packages) with 10-bit accuracy, a programmable Watchdog Timer with Internal Oscillator, an SPI serial
port, and five software selectable power saving modes. The Idle mode stops the CPU while allowing the SRAM,
Timer/Counters, SPI port, and interrupt system to continue functioning. The Power-down mode saves the register
contents but freezes the Oscillator, disabling all other chip functions until the next Interrupt or Hardware Reset. In
Power-save mode, the asynchronous timer continues to run, allowing the user to maintain a timer base while the
rest of the device is sleeping. The ADC Noise Reduction mode stops the CPU and all I/O modules except asyn-
chronous timer and ADC, to minimize switching noise during ADC conversions. In Standby mode, the
crystal/resonator Oscillator is running while the rest of the device is sleeping. This allows very fast start-up com-
bined with low-power consumption.
The device is manufactured using Atmel’s high density non-volatile memory technology. The Flash Program mem-
ory can be reprogrammed In-System through an SPI serial interface, by a conventional non-volatile memory
programmer, or by an On-chip boot program running on the AVR core. The boot program can use any interface to
download the application program in the Application Flash memory. Software in the Boot Flash Section will con-
tinue to run while the Application Flash Section is updated, providing true Read-While-Write operation. By
combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a monolithic chip, the Atmel
ATmega8A is a powerful microcontroller that provides a highly-flexible and cost-effective solution to many embed-
ded control applications.
The Atmel AVR ATmega8A is supported with a full suite of program and system development tools, including C
compilers, macro assemblers, program simulators and evaluation kits.
2.2 Pin Descriptions
2.2.1 VCC
Digital supply voltage.
2.2.2 GND
Ground.
2.2.3
Port B (PB7:PB0) – XTAL1/XTAL2/TOSC1/TOSC2
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port B output buf-
fers 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 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, PB7:6 is used as TOSC2:1 input for the Asyn-
chronous Timer/Counter2 if the AS2 bit in ASSR is set.
ATmega8A [DATASHEET]
4
8159ES–AVR–02/2013
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