Venkat wrote:
(I translated a bit from SMS language...)

Please explain in simple words, if you can

I would like to, Venkat! But, unfortunately, standard Port structure of 80C51 is too complicated...
I highly recommend you to have a look at the '80C51 family hardware description', which you will find here:

http://www.semiconductors.philips.com/acrobat/v...WARE_1.pdf

Have a look at figure 4, 5 and the according text. This, in combination with your datasheet (!), will explain how the ports are working.

Good luck,
Kai