0040h:0000h           RS-232 Communications Line Port Base Addresses

    Length: 8 bytes

    Base addresses for four serial ports. If a port address is 0, then
    that port is not used.

                0040h:0000h - Serial Port #1 (COM1)
                0040h:0002h - Serial Port #2 (COM2)
                0040h:0004h - Serial Port #3 (COM3)
                0040h:0006h - Serial Port #4 (COM4)