Can we use large memory model in Evalation version of Keil for C51.
Your problem is that you're trying to leap into a project before having gained the necessary understanding of the tools.
There are lots of support materials here: http://www.keil.com/support/ including the full set of manuals for the C51 toolset.
Books here: http://www.keil.com/books/8051books.asp
Training: http://www.keil.com/events/links.asp
"i have to use xdata variables so i have to use large memory model"
No, you don't have to.
Read the description of Memory Models again: http://www.keil.com/support/man/docs/c51/c51_le_memmodels.htm
"when we are accessing not more than 256byte of external memory we use pdata"
You can use PDATA - but you don't have to. Also, your hardware needs to be appropriately configured...
"for inernal we use data"
or IDATA.
Note that the terms "internal" and "external" can be misleading in modern devices with on-chip XDATA RAM...
"How to use them in programming"
Please read the manual: http://www.keil.com/support/man/docs/c51/c51_le_memtypes.htm
Thanks for giving links.
I wil study it first and understand. If i have doubt than i will ask you.
Thanks once again...