Button, variables...

[Queops]

Hello there.
I'm kind of a newbie on map making... here's the thing:

I have a func_door which works as a elevator cabin button. Please note that there are also external buttons (in the two floors I have) to call the elevator.

I need the button to know how to output to the func_movelinear, to go up or down either if its at bottom or top floor. And the elevator starts at top floor. How do I make sort of 1 and 0 state?

Thanks