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-- ****

-- T80(b) core. In an effort to merge and maintain bug fixes ....

--

--

-- Ver 300 started tidyup

-- MikeJ March 2005

-- Latest version from www.fpgaarcade.com (original www.opencores.org)

--

-- ****

--

-- Z80 compatible microprocessor core, asynchronous top level

--

-- Version : 0247

--

-- 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 :

--

--      0208 : First complete release

--

--      0211 : Fixed interrupt cycle

--

--      0235 : Updated for T80 interface change

--

--      0238 : Updated for T80 interface change

--

--      0240 : Updated for T80 interface change

--

--      0242 : Updated for T80 interface change

--

--      0247 : Fixed bus req/ack cycle

--

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.numeric_std.all;

use work.T80_Pack.all;

entity T80a is

        generic(

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

        );

        port(

                RESET_n         : in std_logic;

                CLK_n           : 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);

                D                       : inout std_logic_vector(7 downto 0)

        );

end T80a;

architecture rtl of T80a is

        signal CEN                  : std_logic;

        signal Reset_s              : std_logic;

        signal IntCycle_n   : std_logic;

        signal IORQ                 : std_logic;

        signal NoRead               : std_logic;

        signal Write                : std_logic;

        signal MREQ                 : std_logic;

        signal MReq_Inhibit : std_logic;

        signal Req_Inhibit  : std_logic;

        signal RD                   : std_logic;

        signal MREQ_n_i             : std_logic;

        signal IORQ_n_i             : std_logic;

        signal RD_n_i               : std_logic;

        signal WR_n_i               : std_logic;

        signal RFSH_n_i             : std_logic;

        signal BUSAK_n_i    : std_logic;

        signal A_i                  : std_logic_vector(15 downto 0);

        signal DO                   : std_logic_vector(7 downto 0);

        signal DI_Reg               : std_logic_vector (7 downto 0);        -- Input synchroniser

        signal Wait_s               : std_logic;

        signal MCycle               : std_logic_vector(2 downto 0);

        signal TState               : std_logic_vector(2 downto 0);

begin

        CEN <= '1';

        BUSAK_n <= BUSAK_n_i;

        MREQ_n_i <= not MREQ or (Req_Inhibit and MReq_Inhibit);

        RD_n_i <= not RD or Req_Inhibit;

        MREQ_n <= MREQ_n_i when BUSAK_n_i = '1' else 'Z';

        IORQ_n <= IORQ_n_i when BUSAK_n_i = '1' else 'Z';

        RD_n <= RD_n_i when BUSAK_n_i = '1' else 'Z';

        WR_n <= WR_n_i when BUSAK_n_i = '1' else 'Z';

        RFSH_n <= RFSH_n_i when BUSAK_n_i = '1' else 'Z';

        A <= A_i when BUSAK_n_i = '1' else (others => 'Z');

        D <= DO when Write = '1' and BUSAK_n_i = '1' else (others => 'Z');

        process (RESET_n, CLK_n)

        begin

                if RESET_n = '0' then

                        Reset_s <= '0';

                elsif CLK_n'event and CLK_n = '1' then

                        Reset_s <= '1';

                end if;

        end process;

        u0 : T80

                generic map(

                        Mode => Mode,

                        IOWait => 1)

                port map(

                        CEN => CEN,

                        M1_n => M1_n,

                        IORQ => IORQ,

                        NoRead => NoRead,

                        Write => Write,

                        RFSH_n => RFSH_n_i,

                        HALT_n => HALT_n,

                        WAIT_n => Wait_s,

                        INT_n => INT_n,

                        NMI_n => NMI_n,

                        RESET_n => Reset_s,

                        BUSRQ_n => BUSRQ_n,

                        BUSAK_n => BUSAK_n_i,

                        CLK_n => CLK_n,

                        A => A_i,

                        DInst => D,

                        DI => DI_Reg,

                        DO => DO,

                        MC => MCycle,

                        TS => TState,

                        IntCycle_n => IntCycle_n);

        process (CLK_n)

        begin

                if CLK_n'event and CLK_n = '0' then

                        Wait_s <= WAIT_n;

                        if TState = "011" and BUSAK_n_i = '1' then

                                DI_Reg <= to_x01(D);

                        end if;

                end if;

        end process;

        process (Reset_s,CLK_n)

        begin

                if Reset_s = '0' then

                        WR_n_i <= '1';

                elsif CLK_n'event and CLK_n = '1' then

                        WR_n_i <= '1';

                        if TState = "001" then      -- To short for IO writes !!!!!!!!!!!!!!!!!!!

                                WR_n_i <= not Write;

                        end if;

                end if;

        end process;

        process (Reset_s,CLK_n)

        begin

                if Reset_s = '0' then

                        Req_Inhibit <= '0';

                elsif CLK_n'event and CLK_n = '1' then

                        if MCycle = "001" and TState = "010" then

                                Req_Inhibit <= '1';

                        else

                                Req_Inhibit <= '0';

                        end if;

                end if;

        end process;

        process (Reset_s,CLK_n)

        begin

                if Reset_s = '0' then

                        MReq_Inhibit <= '0';

                elsif CLK_n'event and CLK_n = '0' then

                        if MCycle = "001" and TState = "010" then

                                MReq_Inhibit <= '1';

                        else

                                MReq_Inhibit <= '0';

                        end if;

                end if;

        end process;

        process(Reset_s,CLK_n)

        begin

                if Reset_s = '0' then

                        RD <= '0';

                        IORQ_n_i <= '1';

                        MREQ <= '0';

                elsif CLK_n'event and CLK_n = '0' then

                        if MCycle = "001" then

                                if TState = "001" then

                                        RD <= IntCycle_n;

                                        MREQ <= IntCycle_n;

                                        IORQ_n_i <= IntCycle_n;

                                end if;

                                if TState = "011" then

                                        RD <= '0';

                                        IORQ_n_i <= '1';

                                        MREQ <= '1';

                                end if;

                                if TState = "100" then

                                        MREQ <= '0';

                                end if;

                        else

                                if TState = "001" and NoRead = '0' then

                                        RD <= not Write;

                                        IORQ_n_i <= not IORQ;

                                        MREQ <= not IORQ;

                                end if;

                                if TState = "011" then

                                        RD <= '0';

                                        IORQ_n_i <= '1';

                                        MREQ <= '0';

                                end if;

                        end if;

                end if;

        end process;

end;