Hi,
You can interface multiple DS1307 ICs to 89C51 by using multiple I2C Busses. To each of these busses you can also connect other I2C devices like EEPROMS having facility to select device addresses externally.This a penalty you pay for having the convenience of a few pin count device.
Regards, Laktronics
DS1307 has only one address... but if we want to add one more ic DS1307 then we have to take two more pins from microcontroller...
Ok...
Please clear one more doubt...
The address of DS1307 is ' 1101000 '... and we are to send the msb first... and then after sending the 7 bit address we are to receive ACK signal from DS1307 chip...