Int 14 Fn 12  - Pc-mos/386 V5.01 $serial.sys V5.04 - Get Current Port Par  [S]

   AH = 12h
   DX = port number

Return: AH = status
       FFh port number invalid
   AL = line parameters (see #0230)
   AH = flow control configuration (see #0262 at AH=05h"PC-MOS")
   CX:BX = bps rate
   DL = XOFF character or 00h for none
   DH = XON character or 00h for none