The function SSTAT returns either 0 or 1, corresponding to the first or second screen. The function is used to find out which of these screens is currently the visible screen. Unless you have Minerva or Amiga QDOS set up in dual screen mode, this is always 0.
Force the second screen to be displayed (this only works in Minerva or Amiga QDOS):
IF SSTAT = 0 THEN MODE 80,-1