Function 03h (3)         Auxiliary Character Input

    Waits for a character from the standard auxiliary device. Checks for
    Ctrl-Break and Ctrl-C.

       On entry:      AH         03h

       Returns:       AL         Character read

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    This function inputs a character into AL from the standard auxiliary
    device, which is normally the first serial port. (At startup, PC-DOS
    initializes the first serial port to 2400 baud, eight data bits, one
    stop bit, and no parity.)

       Notes:         If a Ctrl-Break (Ctrl-C) is detected, an INT 23h is
                      generated.

                      Input is unbuffered and not interrupt-driven; if
                      your program can't process the characters fast
                      enough, data may be lost.

                      This function does not monitor the status of the
                      serial port. For greater control, use the ROM-BIOS
                      services (Interrupt 14h).