#include <avr/io.h>
#include <avr/interrupt.h>
ISR(ADC_vect)
{
	PORTA = ~ADCH;
}


int main( void )
{

	DDRA  = 0xff;            // PORTB to output
	PORTA = 0Xff;            // All LEDs off

	// Enable ADC. ADC interrupt enable. Free running mode. Prescale=16
	ADCSRA = (1<<ADEN)|(1<<ADIE)|(1<<ADATE)|(1<<ADPS2);
	ADMUX  = (1<<ADLAR) | (1<<REFS0);    // Left-adjust, Ref. = AVCC
	// Single-ended on ADC0 is default

	ADCSRA |= (1<<ADSC);
	sei();

	while(1)
	{
		asm("nop");
	}           // endless loop

}// end main()