Compatibility: 1.0+
Expects: AH    03H
                                                                  
Returns: AL    character fetched from the Standard Auxiliary Device
                                                                  
Info: Reads (waits for) a character from the Standard Auxiliary Device,
COM1 or AUX, returning that character in AL.

Notes:   Input is not buffered and must be polled (not interrupt
driven).

  When DOS starts up, the AUX port (COM1) is initialized to:
2400 baud
no parity
1 stop bit
8-bit word

  The DOS MODE command can be used to initialize various
settings.

See Also: INT 14H
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DOS Fn 03H: Auxiliary Input