Int 14 Fn 19  - Pc-mos/386 V5.01 $serial.sys V5.04 - Selective Buffer Flu  [S]

   AH = 19h
   AL = what to flush
       bit 0: input buffer
       bit 1: output buffer
   DX = port number

Return: nothing

See Also: AH=09h"PC-MOS"