Edge Detection and Other Functions

Edge Detection Functions

The edge detection functions rising_edge() and falling_edge() provide a concise, portable way to describe the behavior of an edge-triggered device such as a flip-flop:

    function rising_edge  (signal s : std_ulogic) return boolean;

    function falling_edge (signal s : std_ulogic) return boolean;

Miscellaneous Checking Functions

The following functions can be used to determine if an object or literal is a don’t-care, which, for this purpose, is defined as any of the five values 'U', 'X', ‘Z', 'W' or '-':

    function Is_X ( s : std_ulogic_vector ) return  boolean;

    function Is_X ( s : std_logic_vector  ) return  boolean;

    function Is_X ( s : std_ulogic ) return  boolean;