Button Scrolling Text

I am trying to let a dynamic text field scroll on 'Hover' over a button.

I have the simple:
on (rollOver) {
info_txt.scroll -= 2;
}

but this simply scrolls the text field 2 lines on the event of rolling onto the button.
How may i acheive getting the text field to continue scrolling untill i roll out?

you need to make a blank mc and put it on the stage and name it scrollControl. then use:

onClipEvent(enterFrame){
_root.info_txt.scroll -= toScroll;
}

then on the buttons put:

on (rollOver) {
scrollControl.toScroll -= 2;
}

on (rollOut){
scrollControl.toScroll = 0;
}

that should do it!