Compatibility: 1.0+
Expects: AH    0bH
                                                                  
Returns: AL    0ffH if a character is available from the Standard Input
0    if no character is available
                                                                  
Info: Checks the status of the Standard Input.

If Ctrl-Break is detected, INT 23H is executed.

Notes:   Use before Fns 01H, 07H, and 08H to avoid having DOS wait for a
key.

  This is a simple, non-destructive way to check for Ctrl-Break
during long calculations or other processing that does not
normally look for input.  It lets the user abort from such a
sequence.

See Also: INT 16H
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DOS Fn 0bH: Check Input Status