Int 15 Fn 86  - Bios - Wait (at,ps)                                        [B]

   AH = 86h
   CX:DX = interval in microseconds

Return: CF clear if successful (wait interval elapsed)
   CF set on error or AH=83h wait already in progress
       AH = status (see #0422)

Note:  the resolution of the wait period is 977 microseconds on many systems
     because many BIOSes use the 1/1024 second fast interrupt from the AT
     real-time clock chip which is available on INT 70; because newer
     BIOSes may have much more precise timers available, it is not
     possible to use this function accurately for very short delays unless
     the precise behavior of the BIOS is known (or found through testing)

See Also: AH=41h,AH=83h,INT 1A/AX=FF01h,INT 70