RTS ds1307 how to read and write the data by using i2c

pls any body tell how to write and read the data by using I2C and how to assign the time date for time keeper register(DS1307).i don't understand the program any body help me.... thanks......


include "16F877A.h"
#use delay(clock=4000000)
#fuses NOWDT,XT, NOPUT, NOPROTECT
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#include "ds1307.c"

void main(void)
{
int8 sec,min,hour,day,date,month,year;

delay_ms(50);
init_ds1307(); // initial DS1307
sec=read_ds1307(0);
write_ds1307(0,sec & 0x7F); // enable oscillator(bit 7 =0) [not understand 0,sec&0x7f]


while(true)
{
sec=read_ds1307(0); // read second
min=read_ds1307(1); // read minute
hour=read_ds1307(2); // read hour
day=read_ds1307(3); // read day
date=read_ds1307(4); // read date
month=read_ds1307(5); // read month
year=read_ds1307(6); // read year
putc(0x0c);
printf("Time : %X:%X:%X\r\n",hour,min,sec);
printf("Day : %02X\r\n",day);
printf("Date : %X/%X/%X\r\n",date,month,year);
delay_ms(500);
}
}




#define DS1307_SDA PIN_C4
#define DS1307_SCL PIN_C3
#use i2c(master, sda=DS1307_SDA, scl=DS1307_SCL)




//==========================
// initial DS1307
//==========================
void init_DS1307()
{
output_float(DS1307_SCL);
output_float(DS1307_SDA);
}
//==========================
// write data one byte to
// DS1307
//==========================
void write_DS1307(byte address, BYTE data)
{
short int status;
i2c_start();
i2c_write(0xd0); [not uderstand,0xd0 its constant for all i2c? ]
i2c_write(address);
i2c_write(data);
i2c_stop();
i2c_start();
status=i2c_write(0xd0);
while(status==1)
{
i2c_start();
status=i2c_write(0xd0);
}
}
//==========================
// read data one byte from DS1307
//==========================
BYTE read_DS1307(byte address)
{
BYTE data;
i2c_start();
i2c_write(0xd0);
i2c_write(address);
i2c_start();
i2c_write(0xd1);
data=i2c_read(0);
i2c_stop();
return(data);
}