Someone can help me how to design as a pause button. It means that when we first active it :=> it is START and next we press again :=> it is PAUSE .and continue
If the start/pause button is operated by a 'human' the dont forget to use 'key debounce' . Well when a human presses a button, it generates a noisy wave before setteling to a logic value. You will have to filter out this 'noise' or nothing would work as expected. Its very simple to do, just look for it in google.
Kr,
Avi http://www.vlsiip.com
If I had understood your question I thing you should use a Finite State Machine.
Electrically speeking avimit gave you a solution if the button will be mechanically activated.