"I have a problem writing a 8051 assembly language code." What's the problem? You should post what you've written to get specific questions answered.

The way to learn programming is by programming...write small programs, make mistakes, debug it to find and fix the problems, then go on to bigger programs. Getting code from someone else won't teach you much (quite often it's more work to use someone else's code than it is to write your own), and certainly is not what your instructor was after when you received this assignment.

In any case, what you're asking for has already been discussed here, with example code and all. Have you done any searching?

Dennis