Int 10 Fn 12  - Video - Alternate Function Select (ps, VGA) - Video Refre  [V]

   AH = 12h
   BL = 36h
   AL = new state
       00h enable refresh
       01h disable refresh

Return: AL = 12h if function supported
Desc:  specify whether the contents of video memory should be displayed on
     the screen; disabling refresh effectively blanks the screen

See Also: AX=BF05h