Program to interface LDR using ADC 0808. The output of LDR is displayed on LCD. Controller interrupt is used to generate the clock for driving ADC 0808.

                     // Program to interface LDR using ADC 0808. The output of LDR is displayed on LCD. Controller interrupt is used to generate the clock for driving ADC 0808.
#include<reg51.h>
sbit ale=P1^0;  //address latch enable
sbit oe=P1^3;  //output enable
sbit sc=P1^1;  //start conversion
sbit eoc=P1^2;  //end of conversion
sbit clk=P1^7;  // clock
sbit ADD_A=P1^4;  // Address pins for selecting input channels.
sbit ADD_B=P1^5;
sbit ADD_C=P1^6;
sfr lcd_data_pin=0xA0;  //P2 port
sbit rs=P3^0;
sbit rw=P3^1;
sbit en=P3^6;
sfr input_port=0x80;  //P0 port
unsigned int bitvalue,decimal_value,key,left_value,value,number,ascii1,ascii2,ascii3,flag,key1;

void timer0() interrupt 1  // Function to generate clock of frequency 500KHZ using Timer 0 interrupt.
{
clk=~clk;
}

void delay(unsigned int count)  // Function to provide time delay in msec.
{
int i,j;
for(i=0;i<count;i++)
for(j=0;j<1275;j++);
}

void lcd_command(unsigned char comm)  //Function to send command to LCD.
{
lcd_data_pin=comm;
en=1;
rs=0;
rw=0;
delay(10);
en=0;
}

void lcd_data(unsigned char disp)  //Function to send data to LCD.
{
lcd_data_pin=disp;
en=1;
rs=1;
rw=0;
delay(10);
en=0;
}

lcd_dataa(unsigned char *disp)  //Function to send string data to LCD.
{
int x;
for(x=0;disp[x]!=0;x++)
{
  lcd_data(disp[x]);
}
}

void lcd_ini()  //Function to inisialize the LCD
{
lcd_command(0x38);
delay(5);
lcd_command(0x0F);
delay(5);
lcd_command(0x80);  //Force cursor to blink at line 1 positon 0
delay(5);
}

  void BCD()  // Binary to decimal conversion to send the data to LCD
{
  key1++;
  key=0;
  flag=0;
    number=input_port;
    value=number%10;
number=number/10;
ascii1=value+48;
if(number!=0)
{
  value=number%10;
  number=number/10;
  ascii2=value+48;
    flag=1;
}
else
{
   ascii2=48;
   flag=1;
}
if(number!=0)
{
  value=number%10;
    number=number/10;
    ascii3=value+48;
    key=2;
}
else
{
  ascii3=48;
  key=2;
}
if(key==2)
lcd_data(ascii3);
if(flag==1)
lcd_data(ascii2);
lcd_data(ascii1);
if(key1==3)
{
key1=0;
ascii3=0;
ascii2=0;
ascii1=0;
delay(10);
}
}

void adc()  //Function to drive ADC
{
while(1)
{
  ADD_C=0;  // Selecting input channel 2 using address lines
  ADD_B=0;
  ADD_A=1;
  delay(2);
  ale=1;
  delay(2);
  sc=1;
  delay(1);
  ale=0;
  delay(1);
  sc=0;
  while(eoc==1);
  while(eoc==0);
  oe=1;
  BCD();
  lcd_command(0x88);
  delay(2);
  oe=0;
}
}

void main()
{
eoc=1;
ale=0;
oe=0;
sc=0;
key1=0;
TMOD=0x02;  //timer0 setting for generating clock of 500KHz using interrupt enable mode.
TH0=0xFD;
IE=0x82;
TR0=1;
lcd_ini();
lcd_dataa("Value : ");
lcd_command(0x88);
adc();
}