What is the exact difference between On-Chip RAM & On-Chip XRAM ? Is the means XRAM means only extended RAM? What is the significance of both?
Have you looked at the instruction set for the processor? Time to do that now.
The processor uses a different set of instructions to access the XRAM memory region.
I would advise that the OP start with the 80C51 family architecture and 80C51 hardware description documents to learn what the difference between the various memory types is before reading the programmers guide.
Links here: www.8052.com/.../120112 Tutorials here: http://www.8052.com/tutorial
Books here: http://www.keil.com/books/8051books.asp