Int 15 Fn 83  - BIOS - Set Event Wait Interval (at,ps50+)                  [B]

   AH = 83h
   AL = subfunction
       00h set interval
       CX:DX = microseconds to delay
       ES:BX -> byte whose high bit is to be set at end of interval
       01h cancel wait interval

Return: CF set on error or function already busy
       AH = status
       80h invalid command (PC,PCjr)
       86h function not supported (XT and later)
   CF clear if successful

Notes: the resolution of the wait period is 977 microseconds on most systems
     because most BIOSes use the 1/1024 second fast interrupt from the AT
     real-time clock chip which is available on INT 70
   IBM AT 1/10/84 BIOS ignores AL and always performs subfunction 00h

See Also: AH=41h,AH=86h,INT 70