Why don't you check the tutorial pages of this site ?

It's all in there.

Other than that:
check intel's site
(www.intel.com)
download atmel's data sheets (www.atmel.com)
or www.dalsemi.com
They have truckloads of datasheet and
application notes.

If that does not help:
www.rigelcorp.com
they have asimulatore and code examples
for the book "Programming and interfacing the 8051 microcontroller"

MUST HAVE !!

Good luck.