Int 14 Fn 1F  - X00 Fossil - Extended Serial Port Status/control           [S]

   AH = 1Fh
   AL = 00h read modem control register

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

         Return: AX = status
   DX = port number

Notes: this function is intended to exactly emulate the PS/2 BIOS AH=05h call
   X00 forces BL bit 3 set (interrupts cannot be disabled)

See Also: AH=00h,AH=05h"SERIAL I/O"

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