ATmega8A-MU datasheet(4/307 Pages) ATMEL

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8159C–AVR–07/09

ATmega8A

The 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 con-

ventional 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 pur-

pose I/O lines, 32 general purpose working registers, three flexible Timer/Counters with

compare modes, internal and external interrupts, a serial programmable 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 asynchro-

nous 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 combined with low-power consumption.

The device is manufactured using Atmel’s high density non-volatile memory technology. The

Flash Program memory 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 continue 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 solu-

tion to many embedded control applications.

The ATmega8A AVR is supported with a full suite of program and system development tools,

including C compilers, macro assemblers, program debugger/simulators, In-Circuit Emulators,

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 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.

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