Hi Ahmed,

Going by your repeated queries you seem to be expecting a null modem to do something it is not meant to !

Your worry is : Having linked up the PC and the MCU, how will the MCU know when the PC wants to send data to it ?

Really you dont have to worry about it. Just read the topic "Serial Interrupt" here: http://www.8052.com/tutint.phtml

And once that concept is clear, that is all there is to it.

And for doing all this ( MCU to PC link ) you just need the Tx, Rx and GND pins. Nothing more nothing less.


Raghu