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;