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                             INT 14H: Serial Port I/O

These functions provide access to the two RS-232 ports supported by BIOS.

The base address of each of up to 4 serial ports is stored starting at
0:0400, but the POST tests for and initializes only the first two serial
ports.
See Asynchronous Adapter Ports for a description of the hardware interface.

AH  Service

00H initialize communications port
      Input: DX = port number (0-1)
             AL = initialization parameter bit flags:

100=1200
                                                           001=150; 101=2400
                                                           010=300; 110=4800
                                                           011=600; 111=9600
     Output: AH = comm status (see below)

01H send a character out the selected RS-232 port
      Input: DX = port number (0-1)
             AL = character to send
     Output: AL is preserved.
             If bit 7 of AH is set, an error occurred and
                AH (bits 6-0) = comm line status (see AH below)

02H receive a character from the selected RS-232 port
      Input: DX = port number (0-1)
     Output: AL is character received
             AH is non-zero if an error occurred