Int 10 Fn 1003  - Video - Toggle Intensity/blinking Bit (jr, Ps, Tandy 10  [V]

   AX = 1003h
   BL = new state
       00h background intensity enabled
       01h blink enabled
   BH = 00h to avoid problems on some adapters

Notes: although there is no function to get the current status on adapters
     prior to the VGA, bit 5 of 0040h:0065h indicates the state; on the
     VGA, use AH=1Bh and check offset 2Dh of the returned data
   when configured for a monochrome display, the Boca Research Multi-EGA
     with ROM v M1.1 Type D has its screen disrupted if BH is not clear

See Also: AH=08h,AH=1Bh