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-- VHDL Entity R6502_TC.Reg_SP.symbol
--
-- Created:
--          by - eda.UNKNOWN (ENTWICKL4-XP-PR)
--          at - 22:53:06 04.01.2009
--
-- Generated by Mentor Graphics' HDL Designer(TM) 2007.1a (Build 13)
--
LIBRARY ieee;
USE ieee.std_logic_1164.all;
USE ieee.std_logic_arith.all;
 
entity Reg_SP is
   port( 
      adr_low_i   : in     std_logic_vector (7 downto 0);
      clk_clk_i   : in     std_logic;
      ld_low_i    : in     std_logic;
      ld_sp_i     : in     std_logic;
      rst_rst_n_i : in     std_logic;
      sel_sp_as_i : in     std_logic;
      sel_sp_in_i : in     std_logic;
      adr_sp_o    : out    std_logic_vector (15 downto 0)
   );
 
-- Declarations
 
end Reg_SP ;
 
-- Jens-D. Gutschmidt     Project:  R6502_TC  
-- scantara2003@yahoo.de                      
-- COPYRIGHT (C) 2008 by Jens Gutschmidt and OPENCORES.ORG                                                                                     
--                                                                                                                                             
-- This program 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 any later version.                                                        
--                                                                                                                                             
-- This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.     
--                                                                                                                                             
-- CVS Revisins History                                                                                                                        
--                                                                                                                                             
-- $Log: not supported by cvs2svn $                                                                                                                         
--   <<-- more -->>                                                                                                                            
-- Title:  Stack Pointer Logic  
-- Path:  R6502_TC/Reg_SP/struct  
-- Edited:  by eda on 01 Jan 2009  
--
-- VHDL Architecture R6502_TC.Reg_SP.struct
--
-- Created:
--          by - eda.UNKNOWN (ENTWICKL4-XP-PR)
--          at - 22:53:06 04.01.2009
--
-- Generated by Mentor Graphics' HDL Designer(TM) 2007.1a (Build 13)
--
LIBRARY ieee;
USE ieee.std_logic_1164.all;
USE ieee.std_logic_arith.all;
 
 
architecture struct of Reg_SP is
 
   -- Architecture declarations
 
   -- Internal signal declarations
   signal adr_sp_low_o_i  : std_logic_vector(7 downto 0);
   signal load_o_i        : std_logic;
   signal result_low1_o_i : std_logic_vector(7 downto 0);
   signal result_low_o_i  : std_logic_vector(7 downto 0);
   signal sp_as_n_o_i     : std_logic;
   signal val_one         : std_logic_vector(7 downto 0);
 
   -- Implicit buffer signal declarations
   signal adr_sp_o_internal : std_logic_vector (15 downto 0);
 
 
   -- ModuleWare signal declarations(v1.9) for instance 'U_11' of 'addsub'
   signal mw_U_11temp_din0 : std_logic_vector(8 downto 0);
   signal mw_U_11temp_din1 : std_logic_vector(8 downto 0);
   signal mw_U_11sum : unsigned(8 downto 0);
 
   -- ModuleWare signal declarations(v1.9) for instance 'U_0' of 'adff'
   signal mw_U_0reg_cval : std_logic_vector(7 downto 0);
 
 
begin
 
   -- ModuleWare code(v1.9) for instance 'U_11' of 'addsub'
   mw_U_11temp_din0 <= '0' & adr_sp_low_o_i;
   mw_U_11temp_din1 <= '0' & val_one;
   u_11combo_proc: process (mw_U_11temp_din0, mw_U_11temp_din1, sp_as_n_o_i)
   variable temp_carry : std_logic;
   begin
      temp_carry := '0';
      if (sp_as_n_o_i = '1') then
         mw_U_11sum <= unsigned(mw_U_11temp_din0) + unsigned(mw_U_11temp_din1) + temp_carry;
      else
         mw_U_11sum <= unsigned(mw_U_11temp_din0) - unsigned(mw_U_11temp_din1) - temp_carry;
      end if;
   end process u_11combo_proc;
   result_low_o_i <= conv_std_logic_vector(mw_U_11sum(7 downto 0),8);
 
   -- ModuleWare code(v1.9) for instance 'U_0' of 'adff'
   adr_sp_o_internal(7 DOWNTO 0) <= mw_U_0reg_cval;
   u_0seq_proc: process (clk_clk_i, rst_rst_n_i)
   begin
      if (rst_rst_n_i = '0') then
         mw_U_0reg_cval <= "00000000";
      elsif (clk_clk_i'event and clk_clk_i='1') then
         if (load_o_i = '1') then
            mw_U_0reg_cval <= result_low1_o_i;
         end if;
      end if;
   end process u_0seq_proc;
 
   -- ModuleWare code(v1.9) for instance 'U_6' of 'and'
   load_o_i <= ld_sp_i and ld_low_i;
 
   -- ModuleWare code(v1.9) for instance 'U_3' of 'buff'
   adr_sp_o_internal(15 DOWNTO 8) <= val_one;
 
   -- ModuleWare code(v1.9) for instance 'U_4' of 'constval'
   val_one <= "00000001";
 
   -- ModuleWare code(v1.9) for instance 'U_2' of 'inv'
   sp_as_n_o_i <= not(sel_sp_as_i);
 
   -- ModuleWare code(v1.9) for instance 'U_8' of 'mux'
   u_8combo_proc: process(result_low_o_i, adr_low_i, sel_sp_in_i)
   begin
      case sel_sp_in_i is
      when '0' => result_low1_o_i <= result_low_o_i;
      when '1' => result_low1_o_i <= adr_low_i;
      when others => result_low1_o_i <= (others => 'X');
      end case;
   end process u_8combo_proc;
 
   -- ModuleWare code(v1.9) for instance 'U_10' of 'tap'
   adr_sp_low_o_i <= adr_sp_o_internal(7 downto 0);
 
   -- Instance port mappings.
 
   -- Implicit buffered output assignments
   adr_sp_o <= adr_sp_o_internal;
 
end struct;