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

Note:  when display refresh is disabled, the entire screen displays the color
     specified by the DAC color register 00h; thus to actually blank the
     screen, the application must first ensure that that register has been
     set to black
BUG:   GEM/VIEWMAX ET3000 and ET4000 drivers dated 6/23/88 do not correctly
     reenable refresh after the screen has been blanked due to inactivity,
     resulting in a total loss of video synchronization

See Also: AX=BF05h