#include <mega16a.h>
#include <delay.h>
#define ADC_VREF_TYPE 0xC0
unsigned int read_adc(unsigned char adc_input)
{
    ADMUX=adc_input | (ADC_VREF_TYPE & 0xff);
    delay_us(100);
    ADCSRA|=0x40;
    while ((ADCSRA & 0x10)==0);
    ADCSRA|=0x10;
    return ADCW;
}
void dac_out(unsigned int value)
{
    PORTC = value & 0xFF;
    PORTD = (value >> 8) & 0xFF;    
}
unsigned int dac_chek(unsigned int address_ADC)
{
        unsigned int out_voltage = 0, flag;
        unsigned int old_voltage, temp;
        flag = 1;
        old_voltage = 0;              
        for (out_voltage = 1; out_voltage <= 7; out_voltage++)
        {                                  
            dac_out(out_voltage << 9);
            delay_ms(5);
            temp = read_adc(address_ADC);
            if (old_voltage + 20 > temp || old_voltage + 20  == temp)
            {
                flag = 0;
                break;
            }
            old_voltage = temp;
        }                      
        return flag;    
}
void init()
{
    PORTA=0x00;
    DDRA=0x00;
    PORTB=0x00;
    DDRB=0xFF;
    PORTC=0x00;
    DDRC=0xFF;
    PORTD=0x00;
    DDRD=0xFF;
    TCCR0=0x00;
    TCNT0=0x00;
    OCR0=0x00;
    TCCR1A=0x00;
    TCCR1B=0x00;
    TCNT1H=0x00;
    TCNT1L=0x00;
    ICR1H=0x00;
    ICR1L=0x00;
    OCR1AH=0x00;
    OCR1AL=0x00;
    OCR1BH=0x00;
    OCR1BL=0x00;
    ASSR=0x00;
    TCCR2=0x00;
    TCNT2=0x00;
    OCR2=0x00;
    MCUCR=0x00;
    MCUCSR=0x00;
    UCSRB=0x00;
    ACSR=0x80;
    SFIOR=0x00;
    ADCSRA=0x87;
    SPCR=0x00;
    TWCR=0x00;
}
void main(void)
{
    unsigned int j, out_data, address;
    init(); 
    PORTB = 0xFF;
    while (1)
    {
        address = 0;
        out_data = 0;
        for(j = 0; j < 4; j++)
        {
            address = 0xC0 | j; 
            if (dac_chek(address))
            {
                out_data |= (1 << j);
            }
            else
            { 
                out_data |= (0x10 << j);
            }
        } 
        PORTB=~out_data;
    }
}