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--

-- Z80 compatible microprocessor core, synchronous top level with clock enable

-- Different timing than the original z80

-- Inputs needs to be synchronous and outputs may glitch

--

-- Version : 0242

--

-- Copyright (c) 2001-2002 Daniel Wallner (jesus@opencores.org)

--

-- All rights reserved

--

-- Redistribution and use in source and synthezised forms, with or without

-- modification, are permitted provided that the following conditions are met:

--

-- Redistributions of source code must retain the above copyright notice,

-- this list of conditions and the following disclaimer.

--

-- Redistributions in synthesized form must reproduce the above copyright

-- notice, this list of conditions and the following disclaimer in the

-- documentation and/or other materials provided with the distribution.

--

-- Neither the name of the author nor the names of other contributors may

-- be used to endorse or promote products derived from this software without

-- specific prior written permission.

--

-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

-- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,

-- THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

-- PURPOSE ARE DISCLAIMED. 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.

--

-- Please report bugs to the author, but before you do so, please

-- make sure that this is not a derivative work and that

-- you have the latest version of this file.

--

-- The latest version of this file can be found at:

--      http://www.opencores.org/cvsweb.shtml/t80/

--

-- Limitations :

--

-- File history :

--

--      0235 : First release

--

--      0236 : Added T2Write generic

--

--      0237 : Fixed T2Write with wait state

--

--      0238 : Updated for T80 interface change

--

--      0240 : Updated for T80 interface change

--

--      0242 : Updated for T80 interface change

--

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.numeric_std.all;

use work.T80_Pack.all;

entity T80se is

        generic(

                Mode : integer := 0;     -- 0 => Z80, 1 => Fast Z80, 2 => 8080, 3 => GB

                T2Write : integer := 0;  -- 0 => WR_n active in T3, /=0 => WR_n active in T2

                IOWait : integer := 1   -- 0 => Single cycle I/O, 1 => Std I/O cycle

        );

        port(

                RESET_n         : in std_logic;

                CLK_n           : in std_logic;

                CLKEN           : in std_logic;

                WAIT_n          : in std_logic;

                INT_n           : in std_logic;

                NMI_n           : in std_logic;

                BUSRQ_n         : in std_logic;

                M1_n            : out std_logic;

                MREQ_n          : out std_logic;

                IORQ_n          : out std_logic;

                RD_n            : out std_logic;

                WR_n            : out std_logic;

                RFSH_n          : out std_logic;

                HALT_n          : out std_logic;

                BUSAK_n         : out std_logic;

                A                       : out std_logic_vector(15 downto 0);

                DI                      : in std_logic_vector(7 downto 0);

                DO                      : out std_logic_vector(7 downto 0)

        );

end T80se;

architecture rtl of T80se is

        signal IntCycle_n       : std_logic;

        signal NoRead           : std_logic;

        signal Write            : std_logic;

        signal IORQ                     : std_logic;

        signal DI_Reg           : std_logic_vector(7 downto 0);

        signal MCycle           : std_logic_vector(2 downto 0);

        signal TState           : std_logic_vector(2 downto 0);

begin

        u0 : T80

                generic map(

                        Mode => Mode,

                        IOWait => IOWait)

                port map(

                        CEN => CLKEN,

                        M1_n => M1_n,

                        IORQ => IORQ,

                        NoRead => NoRead,

                        Write => Write,

                        RFSH_n => RFSH_n,

                        HALT_n => HALT_n,

                        WAIT_n => Wait_n,

                        INT_n => INT_n,

                        NMI_n => NMI_n,

                        RESET_n => RESET_n,

                        BUSRQ_n => BUSRQ_n,

                        BUSAK_n => BUSAK_n,

                        CLK_n => CLK_n,

                        A => A,

                        DInst => DI,

                        DI => DI_Reg,

                        DO => DO,

                        MC => MCycle,

                        TS => TState,

                        IntCycle_n => IntCycle_n);

        process (RESET_n, CLK_n)

        begin

                if RESET_n = '0' then

                        RD_n <= '1';

                        WR_n <= '1';

                        IORQ_n <= '1';

                        MREQ_n <= '1';

                        DI_Reg <= "00000000";

                elsif CLK_n'event and CLK_n = '1' then

                        if CLKEN = '1' then

                                RD_n <= '1';

                                WR_n <= '1';

                                IORQ_n <= '1';

                                MREQ_n <= '1';

                                if MCycle = "001" then

                                        if TState = "001" or (TState = "010" and Wait_n = '0') then

                                                RD_n <= not IntCycle_n;

                                                MREQ_n <= not IntCycle_n;

                                                IORQ_n <= IntCycle_n;

                                        end if;

                                        if TState = "011" then

                                                MREQ_n <= '0';

                                        end if;

                                else

                                        if (TState = "001" or (TState = "010" and Wait_n = '0')) and NoRead = '0' and Write = '0' then

                                                RD_n <= '0';

                                                IORQ_n <= not IORQ;

                                                MREQ_n <= IORQ;

                                        end if;

                                        if T2Write = 0 then

                                                if TState = "010" and Write = '1' then

                                                        WR_n <= '0';

                                                        IORQ_n <= not IORQ;

                                                        MREQ_n <= IORQ;

                                                end if;

                                        else

                                                if (TState = "001" or (TState = "010" and Wait_n = '0')) and Write = '1' then

                                                        WR_n <= '0';

                                                        IORQ_n <= not IORQ;

                                                        MREQ_n <= IORQ;

                                                end if;

                                        end if;

                                end if;

                                if TState = "010" and Wait_n = '1' then

                                        DI_Reg <= DI;

                                end if;

                        end if;

                end if;

        end process;

end;