Int 14 Fn 05  - Serial - Extended Communication Port Control (convertible  [S]

   AH = 05h
   AL = function
       00h read modem control register

         Return: BL = modem control register (see below)
             AH = status
       01h write modem control register
         BL = modem control register (see below)

         Return: AX = status
   DX = port number

Note:  also supported by ArtiCom

See Also: AH=00h,AH=1Fh,AX=8000h"ARTICOM",AH=FBh

Bitfields for modem control register:
 bit 0 data terminal ready
 bit 1 request to send
 bit 2 OUT1
 bit 3 OUT2
 bit 4 LOOP
 bits 5-7 reserved