Function 0Bh (11)        Check Standard Input Status

Checks to see if a character is available from the standard input
device. Checks for Ctrl-Break and Ctrl-C.

On entry:      AH         0Bh

Returns:       AL         FFh       If a character is available
00h       If no character is available

                                                                          

This function can be used to see if a character is available at the
standard input device (usually the keyboard), before transferring
control to one of the waiting keyboard input services (Function 01h,
Function 07h, and Function 08h).

Notes:         The function returns FFh if a character is available
and 00h if none is available.

If DOS encounters a Ctrl-Break or Ctrl-C, it
executes an INT 23h.

See also: 06h
See also: 01h
See also: 07h
See also: 08h

0Bh (11) Check Standard Input Status