Dear Yogesh,

Watch out. You have asked something that is going to make lot of people rush in to reply!

"Can we directly connect T89C51rd2 ports (I/Os) to real world devices "

NO. Never. Use a buffer / driver of some kind. Maybe do a search for " Port Pins " . You will get so many threads enough for a week of reading.

"which pins are to be used for IN and OUT."

That way all pins are bisexual - you can use them either for IN or OUT. ( I know that that the adjective is not very apt - but I couldnt find any better. Sorry). Just write a "1" to the port pin latch and it becomes a INPUT . Simple. ( But please read THE data sheet to further find out subtle differences)

Raghu