Function 04h (4)         Auxiliary Character Output

    Outputs a character to the standard auxiliary device.

       On entry:      AH         04h
                      DL         Character

       Returns:       Nothing

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    This function outputs the character whose ASCII value is in DL to 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 the device is busy, the function waits until it
                      is ready. If a Ctrl-Break or Ctrl-C is detected, INT
                      23h is executed following output.

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