Click above to get retro games delivered to your door ever month!

INT 14h, 05h (05) Control Extended Communications Port           PS/2

     Sets or Reads the Modem Control Register.

   AL = 0 Read Modem Control Register

             On entry:          AH    05h

                                AL      0

                                DX      RS-232C communications line to use
                                        (0, 1, 2, 3)

             Returns:           BL = Modem Control Register
                                        Bit 4 = 1 . Loop
                                        Bit 3 = 1 . Out2
                                        Bit 2 = 1 . Out1
                                        Bit 1 = 1 . Request to send
                                        Bit 0 = 1 . Data terminal ready

                                AL = Modem Status (See Service 03h)

                                AH = Line Status (See Service 03h)

  ---------------------------------------------------------------------------
   AL = 1 Write to Modem Control Register

             On entry:          AH    05h

                                AL      1

                                DX      RS-232C communications line to use
                                        (0, 1, 3)

                                BL = Modem Control Register
                                        Bit 4 = 1 . Loop
                                        Bit 3 = 1 . Out2
                                        Bit 2 = 1 . Out1
                                        Bit 1 = 1 . Request to send
                                        Bit 0 = 1 . Data terminal ready

             Returns:           AL = Modem Status (See Service 03h)

                                AH = Line Status (See Service 03h)

  ---------------------------------------------------------------------------

     With this service, you can read from or write to the modem control
     register. This gives you advanced control over the modem; you can
     configure it a number of ways as shown above. You can also set it to loop
     for diagnostic purposes.

     There are two subservices; Subservice 0 is for reading the modem
     state (returned in BL), and Subservice 1 is for writing to it (set BL
     appropriately). See Service 03h for more information on the modem state.