void init_adc(void)
{	
	DDRA&=~BIT(PA0);
	PORTA&=~BIT(PA0);
    ADCSRA = 0x00; 
    ADMUX =(1<<REFS0)|(adc_mux&0x1f);  	 //AVCC,AREF引腳加濾波電容,單端輸入ADC0
    ADCSRA=(1<<ADEN)|(1<<ADSC)|(1<<ADIE)|(1<<ADPS2)|(1<<ADPS1) ;//64分頻
}

unsigned int mega16_ad()
{
	unsigned int addata;
	DDRA&=~BIT(PA0);
	SFIOR=0;
	ADMUX=0x40;
	
	ADCSR=0X80;
	ADCSR|=BIT(ADSC);
	while(!ADCSR&(BIT(ADIF)));
	addata=addata+ADCH*256;

	ADCSR|=BIT(ADIF);
	ADCSR=0x00; 
	return addata;
}