int ad_convert(void);
void setup() {
  volatile char *dira,*ADMX;
  volatile int value;
  dira=0x30; //port f ddr 
  *dira=0x00; //set as input
  ADMX=0x7C; //address of ADMUX reg of ADC
  *ADMX=0x00;//AREF,data is right adjusted,ADC0 is selected
  Serial.begin(9600);
  
  while(1)
  {
    value=ad_convert(); //ADC function is called and the result is stored in variable value
    Serial.print(value);  //result from ADC is printed
    Serial.print("\t");
    delay(2500);
  }
}
int ad_convert(void)
{
  volatile unsigned char ainlow,*adsl,*adsh;
  volatile char *adcsa;
  volatile unsigned int  ain,ainhigh;
  adcsa=0x7a; //ADC controller and status reg address
  *adcsa=0xc7; //ADC is enabled, conversion started, trigger mode off,prescaler=128
  adsl=0x78; //8 bit result at lower reg 
  adsh=0x79; //2 bit result at higher reg
  while((*adcsa & (1<<4))==0); //when conversion is done ADIF interrupt flag is set.
  
  ainlow=*adsl; //lower 8 bit is copied to variable
  ainhigh=*adsh;// upper 2 bit is copied to variable 
  ainhigh=ainhigh<<8; //2 bits are left shifted to 9th and 10 position
  ain = ainhigh + ainlow; // upper and lower bits are added
  return(ain); //result is returned
}
void loop() {

}