RTC interfacing

#include <reg51.h>


#define I2C_SPEED_FACTOR	1	// Low value means low i2c frequency
#define Crystal_Value		12  // MHz
#define HalfBitDelay 		(500*Crystal_Value)/(12*I2C_SPEED_FACTOR)

#define lcddata P1
sbit SDA= P0^0;
sbit SCL= P0^1;
sbit RS = P2^0;
sbit RW = P2^1;
sbit EN = P2^2;
sbit BSY = P1^7;

/* delay for the clock */
void I2cdelay(unsigned int d)
{
   unsigned int i, limit;
   limit = d/15;
   for(i=0;i<limit;i++);
}

static void delay(unsigned int);


/* initialize the i2c */
static void I2CInit()
{
  SDA = 1;
  SCL = 1;
}

//I2c start
static void I2CStart()
{
 SCL = 1;
 SDA = 1;
 I2cdelay(HalfBitDelay);
 SDA = 0;
 I2cdelay(HalfBitDelay);

}
/* STOP signal to complete the transmission */
static void I2CStop()
{
 SCL = 0;
 I2cdelay(HalfBitDelay/2);
 SDA = 0;
 I2cdelay(HalfBitDelay/2);
 SCL = 1;
 I2cdelay(HalfBitDelay/2);
 SDA = 1;
 I2cdelay(HalfBitDelay/2);
}

/* acknowledge after byte has been received */
static void I2CAck()
{
 SCL = 0;
 I2cdelay(HalfBitDelay/2);
 SDA = 0;
 I2cdelay(HalfBitDelay/2);
 SCL = 1;
 I2cdelay(HalfBitDelay);

}

/* send a no acknowledge to transmitter when all bytes have been received */
static void I2CNak()
{
	SCL = 0;
	I2cdelay(HalfBitDelay/2);
	SDA = 1;
	I2cdelay(HalfBitDelay/2);
	SCL = 1;
	I2cdelay(HalfBitDelay);

}

static void I2CRestart()
{
	SCL = 0;
	I2cdelay(HalfBitDelay/2);
	SDA = 1;
	I2cdelay(HalfBitDelay/2);
	SCL = 1;
	I2cdelay(HalfBitDelay/2);
	SDA = 0;
	I2cdelay(HalfBitDelay/2);
}

/* write data onto the bus */

static unsigned char I2CSend(unsigned char Data)
{
	 unsigned char i;
	 for(i=0;i<8;i++)
	 {
	       /* The data should change on the low clock */

	       SCL = 0;
		   I2cdelay(HalfBitDelay/2);
		   if ((Data & 0x80) == 0)
	       SDA = 0;
		   else
	       SDA = 1;
		   I2cdelay(HalfBitDelay/2);
		   /* keep  SCL high for the valid data */
	       SCL = 1;
		   I2cdelay(HalfBitDelay);
	       Data<<=1;
	 }

     SCL = 0;
	 SDA = 1;
	 I2cdelay(HalfBitDelay);

     SCL = 1;
     I2cdelay(HalfBitDelay);

	 //return ack_bit;
	  return SDA;
}
static unsigned char I2CRead()
{
	unsigned char i, Data=0;

	for(i=0;i<8;i++)
	{
   	    SCL = 0;
		SDA = 1;
		I2cdelay(HalfBitDelay);
		SCL = 1;
		I2cdelay(HalfBitDelay/2);
		if(SDA)
		Data |=0x01;

		if(i<7)
	    Data<<=1;
		I2cdelay(HalfBitDelay/2);

	}



   //SCL = 1;
   return Data;
}





static void lcd_ready()
{
 //make BSY pin as input
  BSY=1;
  //Read out from register
  RS=0;
  //Read
  RW=1;
  while(BSY==1)
  {
    EN=0;
	delay(1);
	EN=1;

  }
}

// delay function
static void delay(unsigned int tme)
{
   unsigned int i,j;
   for(i=0;i<tme;i++)
   for(j=0;j<1275;j++);
}

/*
unsigned char strlen(char str[])
{
   unsigned char len=0,i=0;

   while(str[i++]!='\0')
     len++;

   return len;

}
*/
static void lcd_cmd(unsigned char val)
{
  //check for busy flag
  lcd_ready();
  lcddata=val;
  RS=0;
  RW=0;
  EN=1;
  delay(2);
  EN=0;
}

static void lcd_init()
{
  //16x2 lcd
  lcd_cmd(0x38);
  //clear lcd
  lcd_cmd(0x01);
  //force the cursor to line 1
  lcd_cmd(0x80);
   //display on cursor blinking

   lcd_cmd(0x0E);
}

static void lcd_data(unsigned char datum)
{

	  lcd_ready();
	  lcddata=datum;
	  RS=1;
	  RW=0;
	  EN=1;
	  delay(1);
	  EN=0;

}

static unsigned char convtime(unsigned char hour)
{
      //check for 12 hour or 24 hour mode
  	  if(hour&0x40)
	  {
	     return (hour & 0x1F);
	  }
	  else
	  {
		 return (hour & 0x3F);
	  }

}

static void bcdconv(unsigned char datum)
{
  unsigned char x=0,y=0;
  x=datum&0x0f;
  x=x|0x30;
  y=datum&0xf0;
  y=y>>4;
  y=y|0x30;
  lcd_data(y);
  lcd_data(x);

}

/*
void lcd_data(unsigned char datum[])
{
  unsigned char len=0,i;
  len = strlen(datum);
  for(i=0;i<len;i++)
  {
  //check for busy flag
	  lcd_ready();
	  lcddata=datum[i];
	  RS=1;
	  RW=0;
	  EN=1;
	  delay(1);
	  EN=0;
  }
}
*/


void main()
{

   unsigned char i, a[7],reg_addr=0;
   unsigned int j;
   I2CInit();
   lcd_init();

/* Writing on i2c */
   I2CStart();
   I2CSend(0xD0);
   I2CSend(0x00);
   I2CSend(0x00);
   I2CSend(0x10);
   I2CSend(0x52);
   I2CSend(0x07);
   I2CSend(0x29);
   I2CSend(0x03);
   I2CSend(0x14);
   I2CStop();

   while(1)
   {

					 I2CInit();
					 I2CStart();
					 I2CSend(0xD0);
					 I2CSend(0x00);

					/* Actual read */
					 I2CRestart();

					 I2CSend(0xD1);
					 for(i=0;i<8;i++)
					 {
					      a[i]=I2CRead();
				          if(i==6)
					      I2CNak();
					      else
					      I2CAck();
					 }
				     I2CStop();


			//I2CStop();
			lcd_cmd(0x81);
			bcdconv(convtime(a[2]));
			lcd_data(':');
			bcdconv(a[1]);
			lcd_data(':');
			bcdconv(a[0]);
			lcd_cmd(0xC0);
			bcdconv(a[4]);
			lcd_data('-');
		    bcdconv(a[5]);
			lcd_data('-');
			bcdconv(a[6]);
			for(j=65535;j>0;j--);

   }

}