output of ds1307 to uart using 89v51rd2 is not correct

i'm not familiarize with C just ASM (A51) but i see in your source that
you wrote
for example
min = (DS1307_get(MIN));
and in the subroutine DS1307_get(MIN) min means the adress on the DS1307
but in the main prog you made MIN=0 it should be 1
sec=0 ; min = 1 ; hour = 2 ; day = 4 ; month = 5 ; year = 6

try to be sure that the voltage in the "pin 3" < 1.25 * Vcc

i'm not familiarize with C just ASM (A51) but i see in your source that
you wrote
for example
min = (DS1307_get(MIN));
and in the subroutine DS1307_get(MIN) min means the adress on the DS1307
but in the main prog you made MIN=0 it should be 1
sec=0 ; min = 1 ; hour = 2 ; day = 4 ; month = 5 ; year = 6

try to be sure that the voltage in the "pin 3" < 1.25 * Vcc

unsigned int DS1307_get(unsigned char addr)
{
        unsigned int ret=0;

/* shouldn't you issue a start bit before the write ? */

        I2C_write(DS1307_ID);   /* Connect to DS1307 */
        I2C_write(addr);                /* Request RAM address on DS1307 */

        I2C_start();                    /* Start i2c bus */

        I2C_write(DS1307_ID+1); /* Connect to DS1307 for Read */
        ret = I2C_read();               /* Receive data */

        I2C_noack();

        I2C_stop();                             /* Stop i2c bus */

   return ((((ret>>4)&0x0F)*10)+(ret&0x0F));;
}