-------------------------------------------------------------------------                                                             --------  Generic Up/Down counter (ripple carry architecture)        --------                                                             --------  Author: Richard Herveille                                  --------          richard@asics.ws                                   --------          www.asics.ws                                       --------                                                             -----------------------------------------------------------------------------                                                             -------- Copyright (C) 2001, 2002 Richard Herveille                  --------                          richard@asics.ws                   --------                                                             -------- This source file may be used and distributed without        -------- restriction provided that this copyright statement is not   -------- removed from the file and that any derivative work contains -------- the original copyright notice and the associated disclaimer.--------                                                             --------     THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY     -------- EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED   -------- TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS   -------- FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR      -------- OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,         -------- INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES    -------- (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE   -------- GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR        -------- BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF  -------- LIABILITY, WHETHER IN  CONTRACT, STRICT LIABILITY, OR TORT  -------- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT  -------- OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE         -------- POSSIBILITY OF SUCH DAMAGE.                                 --------                                                             -----------------------------------------------------------------------------  CVS Log----  $Id: ud_cnt.vhd,v 1.1 2002/03/01 03:49:03 rherveille Exp $----  $Date: 2002/03/01 03:49:03 $--  $Revision: 1.1 $--  $Author: rherveille $--  $Locker:  $--  $State: Exp $---- Change History:--               $Log: ud_cnt.vhd,v $--               Revision 1.1  2002/03/01 03:49:03  rherveille--               Changed internal counter libraries.--               Split counter.vhd into separate files.--               Core is in same state as Verilog version now.--library ieee;use ieee.std_logic_1164.all;use ieee.std_logic_arith.all;entity ud_cnt is	generic(		SIZE : natural := 8;		RESD : natural := 0	);	port(		clk    : in  std_logic;                  -- master clock		nReset : in  std_logic := '1';           -- asynchronous active low reset		rst    : in  std_logic := '0';           -- synchronous active high reset		cnt_en : in  std_logic := '1';           -- count enable		ud     : in  std_logic := '0';           -- up / not down		nld    : in  std_logic := '1';           -- synchronous active low load		d      : in  unsigned(SIZE -1 downto 0); -- load counter value		q      : out unsigned(SIZE -1 downto 0); -- current counter value				rci    : in  std_logic := '1';           -- carry input		rco    : out std_logic                   -- carry output	);end entity ud_cnt;architecture structural of ud_cnt is	signal Qi : unsigned(SIZE -1 downto 0);	signal val : unsigned(SIZE downto 0);begin	val <= ( ('0' & Qi) + rci) when (ud = '1') else ( ('0' & Qi) - rci);	regs: process(clk, nReset)	begin		if (nReset = '0') then			Qi <= conv_unsigned(RESD, SIZE);		elsif (clk'event and clk = '1') then			if (rst = '1') then				Qi <= conv_unsigned(RESD, SIZE);			else				if (nld = '0') then					Qi <= D;				elsif (cnt_en = '1') then					Qi <= val(SIZE -1 downto 0);				end if;			end if;		end if;	end process regs;	-- assign outputs	Q <= Qi;	rco <= val(SIZE);end architecture structural;