Subversion Repositories xmatchpro

--This library is free software; you can redistribute it and/or

--modify it under the terms of the GNU Lesser General Public

--License as published by the Free Software Foundation; either

--version 2.1 of the License, or (at your option) any later version.

--This library 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

--Lesser General Public License for more details.

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

--License along with this library; if not, write to the Free Software

--Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

-- e_mail : j.l.nunez-yanez@byacom.co.uk

---------------------------------

--  ENTITY       = MASK_BIT     --

--  version      = 1.0         --

--  last update  = 30/06/01    --

--  author       = Jose Nunez  --

---------------------------------

-- FUNCTION

-- basic bit element of the MASK array

-- reset to zero

--  PIN LIST

--  SEARCH   = input search data bit

--  PREVIOUS = data from the previous location in the array

--  MOVE     = movement control

--  CLEAR    = asynchronous clear of the data latch (active LOW)

--  CLK      = master clock

--  RESET    = asynchronous reset of the data latch (active LOW)

--  DOUT     = output of the data latch

--  MATCH    = indicates a match between search bit and data bit (active LOW)

library ieee;

use ieee.std_logic_1164.all;

entity MASK_BIT is

port

(

        SEARCH : in bit;

        PREVIOUS : in bit;

        MOVE : in bit;

        CLEAR : in bit ;

        RESET : in bit;

        CLK : in bit ;

        DOUT : out bit;

        MATCH : out bit

);

end MASK_BIT;

architecture BIT1 of MASK_BIT is

signal TEMP_D : bit;

signal TEMP_Q : bit;

begin

COMB : process (TEMP_Q , PREVIOUS , MOVE)

begin

if (MOVE = '1') then

                TEMP_D <= PREVIOUS;     -- get data from previous location

else

                TEMP_D <= TEMP_Q;       -- keep current data

end if;

--end if;

end process COMB;

-- mask cleared to 1 so all the data is valid from the start but because all the data is zero only first is real valid

LATCHES : process (CLK,CLEAR)

begin

if (CLEAR = '0') then

        TEMP_Q <= '1';

elsif ((CLK'event) and (CLK = '1')) then

        if (RESET = '0') then

                TEMP_Q <= '1';

        else

                TEMP_Q <= TEMP_D;

        end if;

end if;

end process LATCHES;

DOUT <= TEMP_Q;

MATCH <= SEARCH nand TEMP_Q;            -- match goes low if SEARCH = TEMP_Q = 1

end BIT1;