Int 14 Fn 21  - Hunter 16 - Extended Control                               [S]

   AH = 21h
   AL = command
       01h force transmission of buffer
       02h clear transmit buffer
       03h clear receive buffer
   DX = port (00h COM1, 01h COM2)

Return: AH = extended status
Desc:  executes the command on the selected port

See Also: AH=1Eh"HUNTER",AH=20h"HUNTER",AH=22h"HUNTER",AH=24h"HUNTER"