INT 15 - MultiDOS Plus - FORCE DISPLAY OUTPUT TO PHYSICAL SCREEN MEMORY
AH = 0Bh
Notes:  sets calling task's screen pointer to actual screen memory; the pointer
may be restored with AH=0Ch
caller's video mode must be same as foreground task's video mode
any text written while in the background will be saved to the
foreground task's virtual screen when it switches to the background
useful if a background task wants to display a message on the
foreground screen

See also: 150C

150B - MultiDOS Plus - FORCE DISPLAY OUTPUT TO PHYSICAL SCREEN MEMORY