Well i am trying to upgrade my project which has a keyboard like telephone to PS2 keyboard like computers so I tried to understand the concept of PS2 keyboard. It requires only +5Volt and GND and gives data on SDA line along with clock at SCLK line. I was trying it by putting the clock on the INT0 pin of 89c51 and on every falling edge i was reading the status of the SDA line and then rotating it so after 8 falling edges i should get something which has to be make or break code of the Key. But I am not getting any thing. Suggest me if there is a better way to do the same. Or else what shall I do. If u need the piece of code i wrote can send it. with regards Abhinav.