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  Interrupt:   14h     Function:   05h
 
  Title:       Extended Communications Port Control
 
  Description:                                                    [PS/2]
 
     Reads or sets the modem control register (MCR) for the specified
     serial communications port.
 
     Input                             Output
 
     AH = 05h                          If called with AL = 00h
     AL = Subfunction                    BL = Modem control register
        = 00h Read modem                      contents
              control register
        = 01h Write modem              If called with AL = 01h
              control register           AH = Port status
     BL = Modem control register              See: Int 14h Function 00h
          contents (if AL = 01h)         AL = Modem status
                                              See: Int 14h Function 00h
          Bits     Significance
 
          0        Data-terminal ready
          1        Request-to-send
          2        Out1
          3        Out2
          4        Loop (for testing)
          5-7      Reserved
 
     DX = Communications port number
          (0 = COM1, 1 = COM2,...)
                                    -♦-