Hi Suat Erbay,

Try to download the MCS51 user manual. It is in PDF format available at intel website. You can directly go to the following url:

http://apps.intel.com/scripts-u...=Developer

Remember it is around 15MB stuff and you have to have fast internet connection. Otherwise it will take far lot time.

Or if you can read any book. Also look the buttons on left side of this website (www.8052.com) there are code library, tutorials FAQs and suggestion for books.

Goodluck

Rauf