Andy is right, you should go through the whole learning procedure.

But, to make it easier for you, I'd point few important things:

1) AT89S8252 has internal 8k Flash Program memory and 2k EEPROM Data memory ("82" stands for that). You can not mix these 2!

2) Any of processors with internal ROM will switch to the external program memory only when the program address exceeds the internal range (if EA is high). If your external ROM is mapped at 4k, AT89S8252 cannot address it.

3) How to use EEPROM (again - only for data), you will find in datasheet.

For using AT89... instead of pure 4k 8051, you need to join the external 2k part of program to the basic 4k, program the AT89... and take the external ROM out !


Regards, Slobodan