Hello: I need to implement a few bits from a couple of include files of the AT89S4051 microcontroller. Can someone tell me how should I do it?
Sorry, your question is too vague - please explain fully what you're trying to do.
Have you studied the C51 manuals: https://www.keil.com/support/man_c51.htm ?
8051-specific books: https://www.keil.com/books/8051books.asp
General programming books: https://www.keil.com/books/genbooks.asp