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-- Author : Julian Andres Guarin Reyes.

-- Project : JART, Just Another Ray Tracer.

-- email : jguarin2002 at gmail.com, j.guarin at javeriana.edu.co

-- This code was entirely written by Julian Andres Guarin Reyes.

-- The following code is licensed under GNU Public License

-- http://www.gnu.org/licenses/gpl-3.0.txt.

 -- This file is part of JART (Just Another Ray Tracer).

    -- JART (Just Another Ray Tracer) is free software: you can redistribute it and/or modify

    -- it under the terms of the GNU General Public License as published by

    -- the Free Software Foundation, either version 3 of the License, or

    -- (at your option) any later version.

    -- JART (Just Another Ray Tracer) is distributed in the hope that it will be useful,

    -- but WITHOUT ANY WARRANTY; without even the implied warranty of

    -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    -- GNU General Public License for more details.

    -- You should have received a copy of the GNU General Public License

    -- along with JART (Just Another Ray Tracer).  If not, see <http://www.gnu.org/licenses/>.

-- A scan flipflop hdl code. Note the logic function q <= (s0 and s ) or (s1 and ~s) its a mux with s as selector and s0 and s1 as selectable inputs.

library ieee;

use ieee.std_logic_1164.all;

entity scanFF is

        generic (       W       : integer := 8);

        port    (

                                clk,rst,ena,sel         : std_logic; -- The usual  control signals

                                d0,d1                           : std_logic_vector (W-1 downto 0);       -- The two operands.

                                q                                       : std_logic_vector (W-1 downto 0)        -- The selected data.

        );

end entity;

architecture rtl of scanFF is

begin

        dff_ena_sel : process (clk,rst,ena)

        begin

                if rst = '0' then

                        q <= '0' & (others => '1');

                elsif rising_edge (clk) and ena = '1' then

                        if sel='1' then

                                q <= d1;

                        else

                                q <= d0;

                        end if;

                end if;

        end process;

end rtl;