Since I am unable to post large messages. I am sending this question in parts. Please excuse me!!
Part I
I wanted to program the 8051 so that it will pause/start the clock on pressing one button and restart the clock on pressing another, I did not want to use the reset pin. I wrote a code which incorporated the Bounce delay for the button in the clock subroutine itself, which worked fine. Then I tried another code, given below. With this code, the first time any of the two buttons is pressed, the interrrupt is serviced.