Play / stop button

this is too easy - but I cant work it out…

I have an MC which plays when movie is loaded. I have a button which I want to use to stop the MC playback. Then when it has stopped, have the same button to make it play. Simple… yep … Well my code went like this:

if (roller.stop = true) {
btn.onRelease = function (){
roller.play();
}
}

if (roller.play = true){
btn.onRelease = function () {
roller.stop();
}
}

where have I gone wrrong?

cheers