clocks...

[fpga-games] / galaxian / t80_ip / T80_MCode.vhd

-- ****
-- 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
--
-- 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 :
--
--      0208 : First complete release
--
--      0211 : Fixed IM 1
--
--      0214 : Fixed mostly flags, only the block instructions now fail the zex regression test
--
--      0235 : Added IM 2 fix by Mike Johnson
--
--      0238 : Added NoRead signal
--
--      0238b: Fixed instruction timing for POP and DJNZ
--
--      0240 : Added (IX/IY+d) states, removed op-codes from mode 2 and added all remaining mode 3 op-codes

--      0240mj1 fix for HL inc/dec for INI, IND, INIR, INDR, OUTI, OUTD, OTIR, OTDR
--
--      0242 : Fixed I/O instruction timing, cleanup
--

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.numeric_std.all;
use work.T80_Pack.all;

entity T80_MCode is
	generic(
		Mode : integer := 0;
		Flag_C : integer := 0;
		Flag_N : integer := 1;
		Flag_P : integer := 2;
		Flag_X : integer := 3;
		Flag_H : integer := 4;
		Flag_Y : integer := 5;
		Flag_Z : integer := 6;
		Flag_S : integer := 7
	);
	port(
		IR                              : in std_logic_vector(7 downto 0);
		ISet                    : in std_logic_vector(1 downto 0);
		MCycle                  : in std_logic_vector(2 downto 0);
		F                               : in std_logic_vector(7 downto 0);
		NMICycle                : in std_logic;
		IntCycle                : in std_logic;
		MCycles                 : out std_logic_vector(2 downto 0);
		TStates                 : out std_logic_vector(2 downto 0);
		Prefix                  : out std_logic_vector(1 downto 0); -- None,BC,ED,DD/FD
		Inc_PC                  : out std_logic;
		Inc_WZ                  : out std_logic;
		IncDec_16               : out std_logic_vector(3 downto 0); -- BC,DE,HL,SP   0 is inc
		Read_To_Reg             : out std_logic;
		Read_To_Acc             : out std_logic;
		Set_BusA_To     : out std_logic_vector(3 downto 0); -- B,C,D,E,H,L,DI/DB,A,SP(L),SP(M),0,F
		Set_BusB_To     : out std_logic_vector(3 downto 0); -- B,C,D,E,H,L,DI,A,SP(L),SP(M),1,F,PC(L),PC(M),0
		ALU_Op                  : out std_logic_vector(3 downto 0);
			-- ADD, ADC, SUB, SBC, AND, XOR, OR, CP, ROT, BIT, SET, RES, DAA, RLD, RRD, None
		Save_ALU                : out std_logic;
		PreserveC               : out std_logic;
		Arith16                 : out std_logic;
		Set_Addr_To             : out std_logic_vector(2 downto 0); -- aNone,aXY,aIOA,aSP,aBC,aDE,aZI
		IORQ                    : out std_logic;
		Jump                    : out std_logic;
		JumpE                   : out std_logic;
		JumpXY                  : out std_logic;
		Call                    : out std_logic;
		RstP                    : out std_logic;
		LDZ                             : out std_logic;
		LDW                             : out std_logic;
		LDSPHL                  : out std_logic;
		Special_LD              : out std_logic_vector(2 downto 0); -- A,I;A,R;I,A;R,A;None
		ExchangeDH              : out std_logic;
		ExchangeRp              : out std_logic;
		ExchangeAF              : out std_logic;
		ExchangeRS              : out std_logic;
		I_DJNZ                  : out std_logic;
		I_CPL                   : out std_logic;
		I_CCF                   : out std_logic;
		I_SCF                   : out std_logic;
		I_RETN                  : out std_logic;
		I_BT                    : out std_logic;
		I_BC                    : out std_logic;
		I_BTR                   : out std_logic;
		I_RLD                   : out std_logic;
		I_RRD                   : out std_logic;
		I_INRC                  : out std_logic;
		SetDI                   : out std_logic;
		SetEI                   : out std_logic;
		IMode                   : out std_logic_vector(1 downto 0);
		Halt                    : out std_logic;
		NoRead                  : out std_logic;
		Write                   : out std_logic
	);
end T80_MCode;

architecture rtl of T80_MCode is

	constant aNone      : std_logic_vector(2 downto 0) := "111";
	constant aBC        : std_logic_vector(2 downto 0) := "000";
	constant aDE        : std_logic_vector(2 downto 0) := "001";
	constant aXY        : std_logic_vector(2 downto 0) := "010";
	constant aIOA       : std_logic_vector(2 downto 0) := "100";
	constant aSP        : std_logic_vector(2 downto 0) := "101";
	constant aZI        : std_logic_vector(2 downto 0) := "110";

	function is_cc_true(
		F : std_logic_vector(7 downto 0);
		cc : bit_vector(2 downto 0)
		) return boolean is
	begin
		if Mode = 3 then
			case cc is
			when "000" => return F(7) = '0'; -- NZ
			when "001" => return F(7) = '1'; -- Z
			when "010" => return F(4) = '0'; -- NC
			when "011" => return F(4) = '1'; -- C
			when "100" => return false;
			when "101" => return false;
			when "110" => return false;
			when "111" => return false;
			end case;
		else
			case cc is
			when "000" => return F(6) = '0'; -- NZ
			when "001" => return F(6) = '1'; -- Z
			when "010" => return F(0) = '0'; -- NC
			when "011" => return F(0) = '1'; -- C
			when "100" => return F(2) = '0'; -- PO
			when "101" => return F(2) = '1'; -- PE
			when "110" => return F(7) = '0'; -- P
			when "111" => return F(7) = '1'; -- M
			end case;
		end if;
	end;

begin

	process (IR, ISet, MCycle, F, NMICycle, IntCycle)
		variable DDD : std_logic_vector(2 downto 0);
		variable SSS : std_logic_vector(2 downto 0);
		variable DPair : std_logic_vector(1 downto 0);
		variable IRB : bit_vector(7 downto 0);
	begin
		DDD := IR(5 downto 3);
		SSS := IR(2 downto 0);
		DPair := IR(5 downto 4);
		IRB := to_bitvector(IR);

		MCycles <= "001";
		if MCycle = "001" then
			TStates <= "100";
		else
			TStates <= "011";
		end if;
		Prefix <= "00";
		Inc_PC <= '0';
		Inc_WZ <= '0';
		IncDec_16 <= "0000";
		Read_To_Acc <= '0';
		Read_To_Reg <= '0';
		Set_BusB_To <= "0000";
		Set_BusA_To <= "0000";
		ALU_Op <= "0" & IR(5 downto 3);
		Save_ALU <= '0';
		PreserveC <= '0';
		Arith16 <= '0';
		IORQ <= '0';
		Set_Addr_To <= aNone;
		Jump <= '0';
		JumpE <= '0';
		JumpXY <= '0';
		Call <= '0';
		RstP <= '0';
		LDZ <= '0';
		LDW <= '0';
		LDSPHL <= '0';
		Special_LD <= "000";
		ExchangeDH <= '0';
		ExchangeRp <= '0';
		ExchangeAF <= '0';
		ExchangeRS <= '0';
		I_DJNZ <= '0';
		I_CPL <= '0';
		I_CCF <= '0';
		I_SCF <= '0';
		I_RETN <= '0';
		I_BT <= '0';
		I_BC <= '0';
		I_BTR <= '0';
		I_RLD <= '0';
		I_RRD <= '0';
		I_INRC <= '0';
		SetDI <= '0';
		SetEI <= '0';
		IMode <= "11";
		Halt <= '0';
		NoRead <= '0';
		Write <= '0';

		case ISet is
		when "00" =>

------------------------------------------------------------------------------
--
--      Unprefixed instructions
--
------------------------------------------------------------------------------

		case IRB is
-- 8 BIT LOAD GROUP
		when "01000000"|"01000001"|"01000010"|"01000011"|"01000100"|"01000101"|"01000111"
			|"01001000"|"01001001"|"01001010"|"01001011"|"01001100"|"01001101"|"01001111"
			|"01010000"|"01010001"|"01010010"|"01010011"|"01010100"|"01010101"|"01010111"
			|"01011000"|"01011001"|"01011010"|"01011011"|"01011100"|"01011101"|"01011111"
			|"01100000"|"01100001"|"01100010"|"01100011"|"01100100"|"01100101"|"01100111"
			|"01101000"|"01101001"|"01101010"|"01101011"|"01101100"|"01101101"|"01101111"
			|"01111000"|"01111001"|"01111010"|"01111011"|"01111100"|"01111101"|"01111111" =>
			-- LD r,r'
			Set_BusB_To(2 downto 0) <= SSS;
			ExchangeRp <= '1';
			Set_BusA_To(2 downto 0) <= DDD;
			Read_To_Reg <= '1';
		when "00000110"|"00001110"|"00010110"|"00011110"|"00100110"|"00101110"|"00111110" =>
			-- LD r,n
			MCycles <= "010";
			case to_integer(unsigned(MCycle)) is
			when 2 =>
				Inc_PC <= '1';
				Set_BusA_To(2 downto 0) <= DDD;
				Read_To_Reg <= '1';
			when others => null;
			end case;
		when "01000110"|"01001110"|"01010110"|"01011110"|"01100110"|"01101110"|"01111110" =>
			-- LD r,(HL)
			MCycles <= "010";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aXY;
			when 2 =>
				Set_BusA_To(2 downto 0) <= DDD;
				Read_To_Reg <= '1';
			when others => null;
			end case;
		when "01110000"|"01110001"|"01110010"|"01110011"|"01110100"|"01110101"|"01110111" =>
			-- LD (HL),r
			MCycles <= "010";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aXY;
				Set_BusB_To(2 downto 0) <= SSS;
				Set_BusB_To(3) <= '0';
			when 2 =>
				Write <= '1';
			when others => null;
			end case;
		when "00110110" =>
			-- LD (HL),n
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 2 =>
				Inc_PC <= '1';
				Set_Addr_To <= aXY;
				Set_BusB_To(2 downto 0) <= SSS;
				Set_BusB_To(3) <= '0';
			when 3 =>
				Write <= '1';
			when others => null;
			end case;
		when "00001010" =>
			-- LD A,(BC)
			MCycles <= "010";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aBC;
			when 2 =>
				Read_To_Acc <= '1';
			when others => null;
			end case;
		when "00011010" =>
			-- LD A,(DE)
			MCycles <= "010";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aDE;
			when 2 =>
				Read_To_Acc <= '1';
			when others => null;
			end case;
		when "00111010" =>
			if Mode = 3 then
				-- LDD A,(HL)
				MCycles <= "010";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aXY;
				when 2 =>
					Read_To_Acc <= '1';
					IncDec_16 <= "1110";
				when others => null;
				end case;
			else
				-- LD A,(nn)
				MCycles <= "100";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 3 =>
					Set_Addr_To <= aZI;
					Inc_PC <= '1';
				when 4 =>
					Read_To_Acc <= '1';
				when others => null;
				end case;
			end if;
		when "00000010" =>
			-- LD (BC),A
			MCycles <= "010";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aBC;
				Set_BusB_To <= "0111";
			when 2 =>
				Write <= '1';
			when others => null;
			end case;
		when "00010010" =>
			-- LD (DE),A
			MCycles <= "010";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aDE;
				Set_BusB_To <= "0111";
			when 2 =>
				Write <= '1';
			when others => null;
			end case;
		when "00110010" =>
			if Mode = 3 then
				-- LDD (HL),A
				MCycles <= "010";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aXY;
					Set_BusB_To <= "0111";
				when 2 =>
					Write <= '1';
					IncDec_16 <= "1110";
				when others => null;
				end case;
			else
				-- LD (nn),A
				MCycles <= "100";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 3 =>
					Set_Addr_To <= aZI;
					Inc_PC <= '1';
					Set_BusB_To <= "0111";
				when 4 =>
					Write <= '1';
				when others => null;
				end case;
			end if;

-- 16 BIT LOAD GROUP
		when "00000001"|"00010001"|"00100001"|"00110001" =>
			-- LD dd,nn
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 2 =>
				Inc_PC <= '1';
				Read_To_Reg <= '1';
				if DPAIR = "11" then
					Set_BusA_To(3 downto 0) <= "1000";
				else
					Set_BusA_To(2 downto 1) <= DPAIR;
					Set_BusA_To(0) <= '1';
				end if;
			when 3 =>
				Inc_PC <= '1';
				Read_To_Reg <= '1';
				if DPAIR = "11" then
					Set_BusA_To(3 downto 0) <= "1001";
				else
					Set_BusA_To(2 downto 1) <= DPAIR;
					Set_BusA_To(0) <= '0';
				end if;
			when others => null;
			end case;
		when "00101010" =>
			if Mode = 3 then
				-- LDI A,(HL)
				MCycles <= "010";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aXY;
				when 2 =>
					Read_To_Acc <= '1';
					IncDec_16 <= "0110";
				when others => null;
				end case;
			else
				-- LD HL,(nn)
				MCycles <= "101";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 3 =>
					Set_Addr_To <= aZI;
					Inc_PC <= '1';
					LDW <= '1';
				when 4 =>
					Set_BusA_To(2 downto 0) <= "101"; -- L
					Read_To_Reg <= '1';
					Inc_WZ <= '1';
					Set_Addr_To <= aZI;
				when 5 =>
					Set_BusA_To(2 downto 0) <= "100"; -- H
					Read_To_Reg <= '1';
				when others => null;
				end case;
			end if;
		when "00100010" =>
			if Mode = 3 then
				-- LDI (HL),A
				MCycles <= "010";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aXY;
					Set_BusB_To <= "0111";
				when 2 =>
					Write <= '1';
					IncDec_16 <= "0110";
				when others => null;
				end case;
			else
				-- LD (nn),HL
				MCycles <= "101";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 3 =>
					Set_Addr_To <= aZI;
					Inc_PC <= '1';
					LDW <= '1';
					Set_BusB_To <= "0101"; -- L
				when 4 =>
					Inc_WZ <= '1';
					Set_Addr_To <= aZI;
					Write <= '1';
					Set_BusB_To <= "0100"; -- H
				when 5 =>
					Write <= '1';
				when others => null;
				end case;
			end if;
		when "11111001" =>
			-- LD SP,HL
			TStates <= "110";
			LDSPHL <= '1';
		when "11000101"|"11010101"|"11100101"|"11110101" =>
			-- PUSH qq
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				TStates <= "101";
				IncDec_16 <= "1111";
				Set_Addr_TO <= aSP;
				if DPAIR = "11" then
					Set_BusB_To <= "0111";
				else
					Set_BusB_To(2 downto 1) <= DPAIR;
					Set_BusB_To(0) <= '0';
					Set_BusB_To(3) <= '0';
				end if;
			when 2 =>
				IncDec_16 <= "1111";
				Set_Addr_To <= aSP;
				if DPAIR = "11" then
					Set_BusB_To <= "1011";
				else
					Set_BusB_To(2 downto 1) <= DPAIR;
					Set_BusB_To(0) <= '1';
					Set_BusB_To(3) <= '0';
				end if;
				Write <= '1';
			when 3 =>
				Write <= '1';
			when others => null;
			end case;
		when "11000001"|"11010001"|"11100001"|"11110001" =>
			-- POP qq
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aSP;
			when 2 =>
				IncDec_16 <= "0111";
				Set_Addr_To <= aSP;
				Read_To_Reg <= '1';
				if DPAIR = "11" then
					Set_BusA_To(3 downto 0) <= "1011";
				else
					Set_BusA_To(2 downto 1) <= DPAIR;
					Set_BusA_To(0) <= '1';
				end if;
			when 3 =>
				IncDec_16 <= "0111";
				Read_To_Reg <= '1';
				if DPAIR = "11" then
					Set_BusA_To(3 downto 0) <= "0111";
				else
					Set_BusA_To(2 downto 1) <= DPAIR;
					Set_BusA_To(0) <= '0';
				end if;
			when others => null;
			end case;

-- EXCHANGE, BLOCK TRANSFER AND SEARCH GROUP
		when "11101011" =>
			if Mode /= 3 then
				-- EX DE,HL
				ExchangeDH <= '1';
			end if;
		when "00001000" =>
			if Mode = 3 then
				-- LD (nn),SP
				MCycles <= "101";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 3 =>
					Set_Addr_To <= aZI;
					Inc_PC <= '1';
					LDW <= '1';
					Set_BusB_To <= "1000";
				when 4 =>
					Inc_WZ <= '1';
					Set_Addr_To <= aZI;
					Write <= '1';
					Set_BusB_To <= "1001";
				when 5 =>
					Write <= '1';
				when others => null;
				end case;
			elsif Mode < 2 then
				-- EX AF,AF'
				ExchangeAF <= '1';
			end if;
		when "11011001" =>
			if Mode = 3 then
				-- RETI
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_TO <= aSP;
				when 2 =>
					IncDec_16 <= "0111";
					Set_Addr_To <= aSP;
					LDZ <= '1';
				when 3 =>
					Jump <= '1';
					IncDec_16 <= "0111";
					I_RETN <= '1';
					SetEI <= '1';
				when others => null;
				end case;
			elsif Mode < 2 then
				-- EXX
				ExchangeRS <= '1';
			end if;
		when "11100011" =>
			if Mode /= 3 then
				-- EX (SP),HL
				MCycles <= "101";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aSP;
				when 2 =>
					Read_To_Reg <= '1';
					Set_BusA_To <= "0101";
					Set_BusB_To <= "0101";
					Set_Addr_To <= aSP;
				when 3 =>
					IncDec_16 <= "0111";
					Set_Addr_To <= aSP;
					TStates <= "100";
					Write <= '1';
				when 4 =>
					Read_To_Reg <= '1';
					Set_BusA_To <= "0100";
					Set_BusB_To <= "0100";
					Set_Addr_To <= aSP;
				when 5 =>
					IncDec_16 <= "1111";
					TStates <= "101";
					Write <= '1';
				when others => null;
				end case;
			end if;

-- 8 BIT ARITHMETIC AND LOGICAL GROUP
		when "10000000"|"10000001"|"10000010"|"10000011"|"10000100"|"10000101"|"10000111"
			|"10001000"|"10001001"|"10001010"|"10001011"|"10001100"|"10001101"|"10001111"
			|"10010000"|"10010001"|"10010010"|"10010011"|"10010100"|"10010101"|"10010111"
			|"10011000"|"10011001"|"10011010"|"10011011"|"10011100"|"10011101"|"10011111"
			|"10100000"|"10100001"|"10100010"|"10100011"|"10100100"|"10100101"|"10100111"
			|"10101000"|"10101001"|"10101010"|"10101011"|"10101100"|"10101101"|"10101111"
			|"10110000"|"10110001"|"10110010"|"10110011"|"10110100"|"10110101"|"10110111"
			|"10111000"|"10111001"|"10111010"|"10111011"|"10111100"|"10111101"|"10111111" =>
			-- ADD A,r
			-- ADC A,r
			-- SUB A,r
			-- SBC A,r
			-- AND A,r
			-- OR A,r
			-- XOR A,r
			-- CP A,r
			Set_BusB_To(2 downto 0) <= SSS;
			Set_BusA_To(2 downto 0) <= "111";
			Read_To_Reg <= '1';
			Save_ALU <= '1';
		when "10000110"|"10001110"|"10010110"|"10011110"|"10100110"|"10101110"|"10110110"|"10111110" =>
			-- ADD A,(HL)
			-- ADC A,(HL)
			-- SUB A,(HL)
			-- SBC A,(HL)
			-- AND A,(HL)
			-- OR A,(HL)
			-- XOR A,(HL)
			-- CP A,(HL)
			MCycles <= "010";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aXY;
			when 2 =>
				Read_To_Reg <= '1';
				Save_ALU <= '1';
				Set_BusB_To(2 downto 0) <= SSS;
				Set_BusA_To(2 downto 0) <= "111";
			when others => null;
			end case;
		when "11000110"|"11001110"|"11010110"|"11011110"|"11100110"|"11101110"|"11110110"|"11111110" =>
			-- ADD A,n
			-- ADC A,n
			-- SUB A,n
			-- SBC A,n
			-- AND A,n
			-- OR A,n
			-- XOR A,n
			-- CP A,n
			MCycles <= "010";
			if MCycle = "010" then
				Inc_PC <= '1';
				Read_To_Reg <= '1';
				Save_ALU <= '1';
				Set_BusB_To(2 downto 0) <= SSS;
				Set_BusA_To(2 downto 0) <= "111";
			end if;
		when "00000100"|"00001100"|"00010100"|"00011100"|"00100100"|"00101100"|"00111100" =>
			-- INC r
			Set_BusB_To <= "1010";
			Set_BusA_To(2 downto 0) <= DDD;
			Read_To_Reg <= '1';
			Save_ALU <= '1';
			PreserveC <= '1';
			ALU_Op <= "0000";
		when "00110100" =>
			-- INC (HL)
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aXY;
			when 2 =>
				TStates <= "100";
				Set_Addr_To <= aXY;
				Read_To_Reg <= '1';
				Save_ALU <= '1';
				PreserveC <= '1';
				ALU_Op <= "0000";
				Set_BusB_To <= "1010";
				Set_BusA_To(2 downto 0) <= DDD;
			when 3 =>
				Write <= '1';
			when others => null;
			end case;
		when "00000101"|"00001101"|"00010101"|"00011101"|"00100101"|"00101101"|"00111101" =>
			-- DEC r
			Set_BusB_To <= "1010";
			Set_BusA_To(2 downto 0) <= DDD;
			Read_To_Reg <= '1';
			Save_ALU <= '1';
			PreserveC <= '1';
			ALU_Op <= "0010";
		when "00110101" =>
			-- DEC (HL)
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				Set_Addr_To <= aXY;
			when 2 =>
				TStates <= "100";
				Set_Addr_To <= aXY;
				ALU_Op <= "0010";
				Read_To_Reg <= '1';
				Save_ALU <= '1';
				PreserveC <= '1';
				Set_BusB_To <= "1010";
				Set_BusA_To(2 downto 0) <= DDD;
			when 3 =>
				Write <= '1';
			when others => null;
			end case;

-- GENERAL PURPOSE ARITHMETIC AND CPU CONTROL GROUPS
		when "00100111" =>
			-- DAA
			Set_BusA_To(2 downto 0) <= "111";
			Read_To_Reg <= '1';
			ALU_Op <= "1100";
			Save_ALU <= '1';
		when "00101111" =>
			-- CPL
			I_CPL <= '1';
		when "00111111" =>
			-- CCF
			I_CCF <= '1';
		when "00110111" =>
			-- SCF
			I_SCF <= '1';
		when "00000000" =>
			if NMICycle = '1' then
				-- NMI
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					TStates <= "101";
					IncDec_16 <= "1111";
					Set_Addr_To <= aSP;
					Set_BusB_To <= "1101";
				when 2 =>
					TStates <= "100";
					Write <= '1';
					IncDec_16 <= "1111";
					Set_Addr_To <= aSP;
					Set_BusB_To <= "1100";
				when 3 =>
					TStates <= "100";
					Write <= '1';
				when others => null;
				end case;
			elsif IntCycle = '1' then
				-- INT (IM 2)
				MCycles <= "101";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					LDZ <= '1';
					TStates <= "101";
					IncDec_16 <= "1111";
					Set_Addr_To <= aSP;
					Set_BusB_To <= "1101";
				when 2 =>
					TStates <= "100";
					Write <= '1';
					IncDec_16 <= "1111";
					Set_Addr_To <= aSP;
					Set_BusB_To <= "1100";
				when 3 =>
					TStates <= "100";
					Write <= '1';
				when 4 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 5 =>
					Jump <= '1';
				when others => null;
				end case;
			else
				-- NOP
			end if;
		when "01110110" =>
			-- HALT
			Halt <= '1';
		when "11110011" =>
			-- DI
			SetDI <= '1';
		when "11111011" =>
			-- EI
			SetEI <= '1';

-- 16 BIT ARITHMETIC GROUP
		when "00001001"|"00011001"|"00101001"|"00111001" =>
			-- ADD HL,ss
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 2 =>
				NoRead <= '1';
				ALU_Op <= "0000";
				Read_To_Reg <= '1';
				Save_ALU <= '1';
				Set_BusA_To(2 downto 0) <= "101";
				case to_integer(unsigned(IR(5 downto 4))) is
				when 0|1|2 =>
					Set_BusB_To(2 downto 1) <= IR(5 downto 4);
					Set_BusB_To(0) <= '1';
				when others =>
					Set_BusB_To <= "1000";
				end case;
				TStates <= "100";
				Arith16 <= '1';
			when 3 =>
				NoRead <= '1';
				Read_To_Reg <= '1';
				Save_ALU <= '1';
				ALU_Op <= "0001";
				Set_BusA_To(2 downto 0) <= "100";
				case to_integer(unsigned(IR(5 downto 4))) is
				when 0|1|2 =>
					Set_BusB_To(2 downto 1) <= IR(5 downto 4);
				when others =>
					Set_BusB_To <= "1001";
				end case;
				Arith16 <= '1';
			when others =>
			end case;
		when "00000011"|"00010011"|"00100011"|"00110011" =>
			-- INC ss
			TStates <= "110";
			IncDec_16(3 downto 2) <= "01";
			IncDec_16(1 downto 0) <= DPair;
		when "00001011"|"00011011"|"00101011"|"00111011" =>
			-- DEC ss
			TStates <= "110";
			IncDec_16(3 downto 2) <= "11";
			IncDec_16(1 downto 0) <= DPair;

-- ROTATE AND SHIFT GROUP
		when "00000111"
			-- RLCA
			|"00010111"
			-- RLA
			|"00001111"
			-- RRCA
			|"00011111" =>
			-- RRA
			Set_BusA_To(2 downto 0) <= "111";
			ALU_Op <= "1000";
			Read_To_Reg <= '1';
			Save_ALU <= '1';

-- JUMP GROUP
		when "11000011" =>
			-- JP nn
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 2 =>
				Inc_PC <= '1';
				LDZ <= '1';
			when 3 =>
				Inc_PC <= '1';
				Jump <= '1';
			when others => null;
			end case;
		when "11000010"|"11001010"|"11010010"|"11011010"|"11100010"|"11101010"|"11110010"|"11111010" =>
			if IR(5) = '1' and Mode = 3 then
				case IRB(4 downto 3) is
				when "00" =>
					-- LD ($FF00+C),A
					MCycles <= "010";
					case to_integer(unsigned(MCycle)) is
					when 1 =>
						Set_Addr_To <= aBC;
						Set_BusB_To     <= "0111";
					when 2 =>
						Write <= '1';
						IORQ <= '1';
					when others =>
					end case;
				when "01" =>
					-- LD (nn),A
					MCycles <= "100";
					case to_integer(unsigned(MCycle)) is
					when 2 =>
						Inc_PC <= '1';
						LDZ <= '1';
					when 3 =>
						Set_Addr_To <= aZI;
						Inc_PC <= '1';
						Set_BusB_To <= "0111";
					when 4 =>
						Write <= '1';
					when others => null;
					end case;
				when "10" =>
					-- LD A,($FF00+C)
					MCycles <= "010";
					case to_integer(unsigned(MCycle)) is
					when 1 =>
						Set_Addr_To <= aBC;
					when 2 =>
						Read_To_Acc <= '1';
						IORQ <= '1';
					when others =>
					end case;
				when "11" =>
					-- LD A,(nn)
					MCycles <= "100";
					case to_integer(unsigned(MCycle)) is
					when 2 =>
						Inc_PC <= '1';
						LDZ <= '1';
					when 3 =>
						Set_Addr_To <= aZI;
						Inc_PC <= '1';
					when 4 =>
						Read_To_Acc <= '1';
					when others => null;
					end case;
				end case;
			else
				-- JP cc,nn
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 3 =>
					Inc_PC <= '1';
					if is_cc_true(F, to_bitvector(IR(5 downto 3))) then
						Jump <= '1';
					end if;
				when others => null;
				end case;
			end if;
		when "00011000" =>
			if Mode /= 2 then
				-- JR e
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
				when 3 =>
					NoRead <= '1';
					JumpE <= '1';
					TStates <= "101";
				when others => null;
				end case;
			end if;
		when "00111000" =>
			if Mode /= 2 then
				-- JR C,e
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					if F(Flag_C) = '0' then
						MCycles <= "010";
					end if;
				when 3 =>
					NoRead <= '1';
					JumpE <= '1';
					TStates <= "101";
				when others => null;
				end case;
			end if;
		when "00110000" =>
			if Mode /= 2 then
				-- JR NC,e
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					if F(Flag_C) = '1' then
						MCycles <= "010";
					end if;
				when 3 =>
					NoRead <= '1';
					JumpE <= '1';
					TStates <= "101";
				when others => null;
				end case;
			end if;
		when "00101000" =>
			if Mode /= 2 then
				-- JR Z,e
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					if F(Flag_Z) = '0' then
						MCycles <= "010";
					end if;
				when 3 =>
					NoRead <= '1';
					JumpE <= '1';
					TStates <= "101";
				when others => null;
				end case;
			end if;
		when "00100000" =>
			if Mode /= 2 then
				-- JR NZ,e
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					if F(Flag_Z) = '1' then
						MCycles <= "010";
					end if;
				when 3 =>
					NoRead <= '1';
					JumpE <= '1';
					TStates <= "101";
				when others => null;
				end case;
			end if;
		when "11101001" =>
			-- JP (HL)
			JumpXY <= '1';
		when "00010000" =>
			if Mode = 3 then
				I_DJNZ <= '1';
			elsif Mode < 2 then
				-- DJNZ,e
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					TStates <= "101";
					I_DJNZ <= '1';
					Set_BusB_To <= "1010";
					Set_BusA_To(2 downto 0) <= "000";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					ALU_Op <= "0010";
				when 2 =>
					I_DJNZ <= '1';
					Inc_PC <= '1';
				when 3 =>
					NoRead <= '1';
					JumpE <= '1';
					TStates <= "101";
				when others => null;
				end case;
			end if;

-- CALL AND RETURN GROUP
		when "11001101" =>
			-- CALL nn
			MCycles <= "101";
			case to_integer(unsigned(MCycle)) is
			when 2 =>
				Inc_PC <= '1';
				LDZ <= '1';
			when 3 =>
				IncDec_16 <= "1111";
				Inc_PC <= '1';
				TStates <= "100";
				Set_Addr_To <= aSP;
				LDW <= '1';
				Set_BusB_To <= "1101";
			when 4 =>
				Write <= '1';
				IncDec_16 <= "1111";
				Set_Addr_To <= aSP;
				Set_BusB_To <= "1100";
			when 5 =>
				Write <= '1';
				Call <= '1';
			when others => null;
			end case;
		when "11000100"|"11001100"|"11010100"|"11011100"|"11100100"|"11101100"|"11110100"|"11111100" =>
			if IR(5) = '0' or Mode /= 3 then
				-- CALL cc,nn
				MCycles <= "101";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 3 =>
					Inc_PC <= '1';
					LDW <= '1';
					if is_cc_true(F, to_bitvector(IR(5 downto 3))) then
						IncDec_16 <= "1111";
						Set_Addr_TO <= aSP;
						TStates <= "100";
						Set_BusB_To <= "1101";
					else
						MCycles <= "011";
					end if;
				when 4 =>
					Write <= '1';
					IncDec_16 <= "1111";
					Set_Addr_To <= aSP;
					Set_BusB_To <= "1100";
				when 5 =>
					Write <= '1';
					Call <= '1';
				when others => null;
				end case;
			end if;
		when "11001001" =>
			-- RET
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				TStates <= "101";
				Set_Addr_TO <= aSP;
			when 2 =>
				IncDec_16 <= "0111";
				Set_Addr_To <= aSP;
				LDZ <= '1';
			when 3 =>
				Jump <= '1';
				IncDec_16 <= "0111";
			when others => null;
			end case;
		when "11000000"|"11001000"|"11010000"|"11011000"|"11100000"|"11101000"|"11110000"|"11111000" =>
			if IR(5) = '1' and Mode = 3 then
				case IRB(4 downto 3) is
				when "00" =>
					-- LD ($FF00+nn),A
					MCycles <= "011";
					case to_integer(unsigned(MCycle)) is
					when 2 =>
						Inc_PC <= '1';
						Set_Addr_To <= aIOA;
						Set_BusB_To     <= "0111";
					when 3 =>
						Write <= '1';
					when others => null;
					end case;
				when "01" =>
					-- ADD SP,n
					MCycles <= "011";
					case to_integer(unsigned(MCycle)) is
					when 2 =>
						ALU_Op <= "0000";
						Inc_PC <= '1';
						Read_To_Reg <= '1';
						Save_ALU <= '1';
						Set_BusA_To <= "1000";
						Set_BusB_To <= "0110";
					when 3 =>
						NoRead <= '1';
						Read_To_Reg <= '1';
						Save_ALU <= '1';
						ALU_Op <= "0001";
						Set_BusA_To <= "1001";
						Set_BusB_To <= "1110";  -- Incorrect unsigned !!!!!!!!!!!!!!!!!!!!!
					when others =>
					end case;
				when "10" =>
					-- LD A,($FF00+nn)
					MCycles <= "011";
					case to_integer(unsigned(MCycle)) is
					when 2 =>
						Inc_PC <= '1';
						Set_Addr_To <= aIOA;
					when 3 =>
						Read_To_Acc <= '1';
					when others => null;
					end case;
				when "11" =>
					-- LD HL,SP+n       -- Not correct !!!!!!!!!!!!!!!!!!!
					MCycles <= "101";
					case to_integer(unsigned(MCycle)) is
					when 2 =>
						Inc_PC <= '1';
						LDZ <= '1';
					when 3 =>
						Set_Addr_To <= aZI;
						Inc_PC <= '1';
						LDW <= '1';
					when 4 =>
						Set_BusA_To(2 downto 0) <= "101"; -- L
						Read_To_Reg <= '1';
						Inc_WZ <= '1';
						Set_Addr_To <= aZI;
					when 5 =>
						Set_BusA_To(2 downto 0) <= "100"; -- H
						Read_To_Reg <= '1';
					when others => null;
					end case;
				end case;
			else
				-- RET cc
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					if is_cc_true(F, to_bitvector(IR(5 downto 3))) then
						Set_Addr_TO <= aSP;
					else
						MCycles <= "001";
					end if;
					TStates <= "101";
				when 2 =>
					IncDec_16 <= "0111";
					Set_Addr_To <= aSP;
					LDZ <= '1';
				when 3 =>
					Jump <= '1';
					IncDec_16 <= "0111";
				when others => null;
				end case;
			end if;
		when "11000111"|"11001111"|"11010111"|"11011111"|"11100111"|"11101111"|"11110111"|"11111111" =>
			-- RST p
			MCycles <= "011";
			case to_integer(unsigned(MCycle)) is
			when 1 =>
				TStates <= "101";
				IncDec_16 <= "1111";
				Set_Addr_To <= aSP;
				Set_BusB_To <= "1101";
			when 2 =>
				Write <= '1';
				IncDec_16 <= "1111";
				Set_Addr_To <= aSP;
				Set_BusB_To <= "1100";
			when 3 =>
				Write <= '1';
				RstP <= '1';
			when others => null;
			end case;

-- INPUT AND OUTPUT GROUP
		when "11011011" =>
			if Mode /= 3 then
				-- IN A,(n)
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					Set_Addr_To <= aIOA;
				when 3 =>
					Read_To_Acc <= '1';
					IORQ <= '1';
				when others => null;
				end case;
			end if;
		when "11010011" =>
			if Mode /= 3 then
				-- OUT (n),A
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					Set_Addr_To <= aIOA;
					Set_BusB_To <= "0111";
				when 3 =>
					Write <= '1';
					IORQ <= '1';
				when others => null;
				end case;
			end if;

------------------------------------------------------------------------------
------------------------------------------------------------------------------
-- MULTIBYTE INSTRUCTIONS
------------------------------------------------------------------------------
------------------------------------------------------------------------------

		when "11001011" =>
			if Mode /= 2 then
				Prefix <= "01";
			end if;

		when "11101101" =>
			if Mode < 2 then
				Prefix <= "10";
			end if;

		when "11011101"|"11111101" =>
			if Mode < 2 then
				Prefix <= "11";
			end if;

		end case;

		when "01" =>

------------------------------------------------------------------------------
--
--      CB prefixed instructions
--
------------------------------------------------------------------------------

			Set_BusA_To(2 downto 0) <= IR(2 downto 0);
			Set_BusB_To(2 downto 0) <= IR(2 downto 0);

			case IRB is
			when "00000000"|"00000001"|"00000010"|"00000011"|"00000100"|"00000101"|"00000111"
				|"00010000"|"00010001"|"00010010"|"00010011"|"00010100"|"00010101"|"00010111"
				|"00001000"|"00001001"|"00001010"|"00001011"|"00001100"|"00001101"|"00001111"
				|"00011000"|"00011001"|"00011010"|"00011011"|"00011100"|"00011101"|"00011111"
				|"00100000"|"00100001"|"00100010"|"00100011"|"00100100"|"00100101"|"00100111"
				|"00101000"|"00101001"|"00101010"|"00101011"|"00101100"|"00101101"|"00101111"
				|"00110000"|"00110001"|"00110010"|"00110011"|"00110100"|"00110101"|"00110111"
				|"00111000"|"00111001"|"00111010"|"00111011"|"00111100"|"00111101"|"00111111" =>
				-- RLC r
				-- RL r
				-- RRC r
				-- RR r
				-- SLA r
				-- SRA r
				-- SRL r
				-- SLL r (Undocumented) / SWAP r
				if MCycle = "001" then
				  ALU_Op <= "1000";
				  Read_To_Reg <= '1';
				  Save_ALU <= '1';
				end if;
			when "00000110"|"00010110"|"00001110"|"00011110"|"00101110"|"00111110"|"00100110"|"00110110" =>
				-- RLC (HL)
				-- RL (HL)
				-- RRC (HL)
				-- RR (HL)
				-- SRA (HL)
				-- SRL (HL)
				-- SLA (HL)
				-- SLL (HL) (Undocumented) / SWAP (HL)
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 1 | 7 =>
					Set_Addr_To <= aXY;
				when 2 =>
					ALU_Op <= "1000";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					Set_Addr_To <= aXY;
					TStates <= "100";
				when 3 =>
					Write <= '1';
				when others =>
				end case;
			when "01000000"|"01000001"|"01000010"|"01000011"|"01000100"|"01000101"|"01000111"
				|"01001000"|"01001001"|"01001010"|"01001011"|"01001100"|"01001101"|"01001111"
				|"01010000"|"01010001"|"01010010"|"01010011"|"01010100"|"01010101"|"01010111"
				|"01011000"|"01011001"|"01011010"|"01011011"|"01011100"|"01011101"|"01011111"
				|"01100000"|"01100001"|"01100010"|"01100011"|"01100100"|"01100101"|"01100111"
				|"01101000"|"01101001"|"01101010"|"01101011"|"01101100"|"01101101"|"01101111"
				|"01110000"|"01110001"|"01110010"|"01110011"|"01110100"|"01110101"|"01110111"
				|"01111000"|"01111001"|"01111010"|"01111011"|"01111100"|"01111101"|"01111111" =>
				-- BIT b,r
				if MCycle = "001" then
				  Set_BusB_To(2 downto 0) <= IR(2 downto 0);
				  ALU_Op <= "1001";
				end if;
			when "01000110"|"01001110"|"01010110"|"01011110"|"01100110"|"01101110"|"01110110"|"01111110" =>
				-- BIT b,(HL)
				MCycles <= "010";
				case to_integer(unsigned(MCycle)) is
				when 1 | 7=>
					Set_Addr_To <= aXY;
				when 2 =>
					ALU_Op <= "1001";
					TStates <= "100";
				when others => null;
				end case;
			when "11000000"|"11000001"|"11000010"|"11000011"|"11000100"|"11000101"|"11000111"
				|"11001000"|"11001001"|"11001010"|"11001011"|"11001100"|"11001101"|"11001111"
				|"11010000"|"11010001"|"11010010"|"11010011"|"11010100"|"11010101"|"11010111"
				|"11011000"|"11011001"|"11011010"|"11011011"|"11011100"|"11011101"|"11011111"
				|"11100000"|"11100001"|"11100010"|"11100011"|"11100100"|"11100101"|"11100111"
				|"11101000"|"11101001"|"11101010"|"11101011"|"11101100"|"11101101"|"11101111"
				|"11110000"|"11110001"|"11110010"|"11110011"|"11110100"|"11110101"|"11110111"
				|"11111000"|"11111001"|"11111010"|"11111011"|"11111100"|"11111101"|"11111111" =>
				-- SET b,r
				if MCycle = "001" then
				  ALU_Op <= "1010";
				  Read_To_Reg <= '1';
				  Save_ALU <= '1';
				end if;
			when "11000110"|"11001110"|"11010110"|"11011110"|"11100110"|"11101110"|"11110110"|"11111110" =>
				-- SET b,(HL)
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 1 | 7=>
					Set_Addr_To <= aXY;
				when 2 =>
					ALU_Op <= "1010";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					Set_Addr_To <= aXY;
					TStates <= "100";
				when 3 =>
					Write <= '1';
				when others => null;
				end case;
			when "10000000"|"10000001"|"10000010"|"10000011"|"10000100"|"10000101"|"10000111"
				|"10001000"|"10001001"|"10001010"|"10001011"|"10001100"|"10001101"|"10001111"
				|"10010000"|"10010001"|"10010010"|"10010011"|"10010100"|"10010101"|"10010111"
				|"10011000"|"10011001"|"10011010"|"10011011"|"10011100"|"10011101"|"10011111"
				|"10100000"|"10100001"|"10100010"|"10100011"|"10100100"|"10100101"|"10100111"
				|"10101000"|"10101001"|"10101010"|"10101011"|"10101100"|"10101101"|"10101111"
				|"10110000"|"10110001"|"10110010"|"10110011"|"10110100"|"10110101"|"10110111"
				|"10111000"|"10111001"|"10111010"|"10111011"|"10111100"|"10111101"|"10111111" =>
				-- RES b,r
				if MCycle = "001" then
					ALU_Op <= "1011";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
				end if;
			when "10000110"|"10001110"|"10010110"|"10011110"|"10100110"|"10101110"|"10110110"|"10111110" =>
				-- RES b,(HL)
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 1 | 7 =>
					Set_Addr_To <= aXY;
				when 2 =>
					ALU_Op <= "1011";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					Set_Addr_To <= aXY;
					TStates <= "100";
				when 3 =>
					Write <= '1';
				when others => null;
				end case;
			end case;

		when others =>

------------------------------------------------------------------------------
--
--      ED prefixed instructions
--
------------------------------------------------------------------------------

			case IRB is
			when "00000000"|"00000001"|"00000010"|"00000011"|"00000100"|"00000101"|"00000110"|"00000111"
				|"00001000"|"00001001"|"00001010"|"00001011"|"00001100"|"00001101"|"00001110"|"00001111"
				|"00010000"|"00010001"|"00010010"|"00010011"|"00010100"|"00010101"|"00010110"|"00010111"
				|"00011000"|"00011001"|"00011010"|"00011011"|"00011100"|"00011101"|"00011110"|"00011111"
				|"00100000"|"00100001"|"00100010"|"00100011"|"00100100"|"00100101"|"00100110"|"00100111"
				|"00101000"|"00101001"|"00101010"|"00101011"|"00101100"|"00101101"|"00101110"|"00101111"
				|"00110000"|"00110001"|"00110010"|"00110011"|"00110100"|"00110101"|"00110110"|"00110111"
				|"00111000"|"00111001"|"00111010"|"00111011"|"00111100"|"00111101"|"00111110"|"00111111"


				|"10000000"|"10000001"|"10000010"|"10000011"|"10000100"|"10000101"|"10000110"|"10000111"
				|"10001000"|"10001001"|"10001010"|"10001011"|"10001100"|"10001101"|"10001110"|"10001111"
				|"10010000"|"10010001"|"10010010"|"10010011"|"10010100"|"10010101"|"10010110"|"10010111"
				|"10011000"|"10011001"|"10011010"|"10011011"|"10011100"|"10011101"|"10011110"|"10011111"
				|                                            "10100100"|"10100101"|"10100110"|"10100111"
				|                                            "10101100"|"10101101"|"10101110"|"10101111"
				|                                            "10110100"|"10110101"|"10110110"|"10110111"
				|                                            "10111100"|"10111101"|"10111110"|"10111111"
				|"11000000"|"11000001"|"11000010"|"11000011"|"11000100"|"11000101"|"11000110"|"11000111"
				|"11001000"|"11001001"|"11001010"|"11001011"|"11001100"|"11001101"|"11001110"|"11001111"
				|"11010000"|"11010001"|"11010010"|"11010011"|"11010100"|"11010101"|"11010110"|"11010111"
				|"11011000"|"11011001"|"11011010"|"11011011"|"11011100"|"11011101"|"11011110"|"11011111"
				|"11100000"|"11100001"|"11100010"|"11100011"|"11100100"|"11100101"|"11100110"|"11100111"
				|"11101000"|"11101001"|"11101010"|"11101011"|"11101100"|"11101101"|"11101110"|"11101111"
				|"11110000"|"11110001"|"11110010"|"11110011"|"11110100"|"11110101"|"11110110"|"11110111"
				|"11111000"|"11111001"|"11111010"|"11111011"|"11111100"|"11111101"|"11111110"|"11111111" =>
				null; -- NOP, undocumented
			when "01111110"|"01111111" =>
				-- NOP, undocumented
				null;
-- 8 BIT LOAD GROUP
			when "01010111" =>
				-- LD A,I
				Special_LD <= "100";
				TStates <= "101";
			when "01011111" =>
				-- LD A,R
				Special_LD <= "101";
				TStates <= "101";
			when "01000111" =>
				-- LD I,A
				Special_LD <= "110";
				TStates <= "101";
			when "01001111" =>
				-- LD R,A
				Special_LD <= "111";
				TStates <= "101";
-- 16 BIT LOAD GROUP
			when "01001011"|"01011011"|"01101011"|"01111011" =>
				-- LD dd,(nn)
				MCycles <= "101";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 3 =>
					Set_Addr_To <= aZI;
					Inc_PC <= '1';
					LDW <= '1';
				when 4 =>
					Read_To_Reg <= '1';
					if IR(5 downto 4) = "11" then
						Set_BusA_To <= "1000";
					else
						Set_BusA_To(2 downto 1) <= IR(5 downto 4);
						Set_BusA_To(0) <= '1';
					end if;
					Inc_WZ <= '1';
					Set_Addr_To <= aZI;
				when 5 =>
					Read_To_Reg <= '1';
					if IR(5 downto 4) = "11" then
						Set_BusA_To <= "1001";
					else
						Set_BusA_To(2 downto 1) <= IR(5 downto 4);
						Set_BusA_To(0) <= '0';
					end if;
				when others => null;
				end case;
			when "01000011"|"01010011"|"01100011"|"01110011" =>
				-- LD (nn),dd
				MCycles <= "101";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Inc_PC <= '1';
					LDZ <= '1';
				when 3 =>
					Set_Addr_To <= aZI;
					Inc_PC <= '1';
					LDW <= '1';
					if IR(5 downto 4) = "11" then
						Set_BusB_To <= "1000";
					else
						Set_BusB_To(2 downto 1) <= IR(5 downto 4);
						Set_BusB_To(0) <= '1';
						Set_BusB_To(3) <= '0';
					end if;
				when 4 =>
					Inc_WZ <= '1';
					Set_Addr_To <= aZI;
					Write <= '1';
					if IR(5 downto 4) = "11" then
						Set_BusB_To <= "1001";
					else
						Set_BusB_To(2 downto 1) <= IR(5 downto 4);
						Set_BusB_To(0) <= '0';
						Set_BusB_To(3) <= '0';
					end if;
				when 5 =>
					Write <= '1';
				when others => null;
				end case;
			when "10100000" | "10101000" | "10110000" | "10111000" =>
				-- LDI, LDD, LDIR, LDDR
				MCycles <= "100";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aXY;
					IncDec_16 <= "1100"; -- BC
				when 2 =>
					Set_BusB_To <= "0110";
					Set_BusA_To(2 downto 0) <= "111";
					ALU_Op <= "0000";
					Set_Addr_To <= aDE;
					if IR(3) = '0' then
						IncDec_16 <= "0110"; -- IX
					else
						IncDec_16 <= "1110";
					end if;
				when 3 =>
					I_BT <= '1';
					TStates <= "101";
					Write <= '1';
					if IR(3) = '0' then
						IncDec_16 <= "0101"; -- DE
					else
						IncDec_16 <= "1101";
					end if;
				when 4 =>
					NoRead <= '1';
					TStates <= "101";
				when others => null;
				end case;
			when "10100001" | "10101001" | "10110001" | "10111001" =>
				-- CPI, CPD, CPIR, CPDR
				MCycles <= "100";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aXY;
					IncDec_16 <= "1100"; -- BC
				when 2 =>
					Set_BusB_To <= "0110";
					Set_BusA_To(2 downto 0) <= "111";
					ALU_Op <= "0111";
					Save_ALU <= '1';
					PreserveC <= '1';
					if IR(3) = '0' then
						IncDec_16 <= "0110";
					else
						IncDec_16 <= "1110";
					end if;
				when 3 =>
					NoRead <= '1';
					I_BC <= '1';
					TStates <= "101";
				when 4 =>
					NoRead <= '1';
					TStates <= "101";
				when others => null;
				end case;
			when "01000100"|"01001100"|"01010100"|"01011100"|"01100100"|"01101100"|"01110100"|"01111100" =>
				-- NEG
				Alu_OP <= "0010";
				Set_BusB_To <= "0111";
				Set_BusA_To <= "1010";
				Read_To_Acc <= '1';
				Save_ALU <= '1';
			when "01000110"|"01001110"|"01100110"|"01101110" =>
				-- IM 0
				IMode <= "00";
			when "01010110"|"01110110" =>
				-- IM 1
				IMode <= "01";
			when "01011110"|"01110111" =>
				-- IM 2
				IMode <= "10";
-- 16 bit arithmetic
			when "01001010"|"01011010"|"01101010"|"01111010" =>
				-- ADC HL,ss
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					NoRead <= '1';
					ALU_Op <= "0001";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					Set_BusA_To(2 downto 0) <= "101";
					case to_integer(unsigned(IR(5 downto 4))) is
					when 0|1|2 =>
						Set_BusB_To(2 downto 1) <= IR(5 downto 4);
					Set_BusB_To(0) <= '1';
						when others =>
						Set_BusB_To <= "1000";
					end case;
					TStates <= "100";
				when 3 =>
					NoRead <= '1';
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					ALU_Op <= "0001";
					Set_BusA_To(2 downto 0) <= "100";
					case to_integer(unsigned(IR(5 downto 4))) is
					when 0|1|2 =>
						Set_BusB_To(2 downto 1) <= IR(5 downto 4);
						Set_BusB_To(0) <= '0';
					when others =>
						Set_BusB_To <= "1001";
					end case;
				when others =>
				end case;
			when "01000010"|"01010010"|"01100010"|"01110010" =>
				-- SBC HL,ss
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					NoRead <= '1';
					ALU_Op <= "0011";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					Set_BusA_To(2 downto 0) <= "101";
					case to_integer(unsigned(IR(5 downto 4))) is
					when 0|1|2 =>
						Set_BusB_To(2 downto 1) <= IR(5 downto 4);
						Set_BusB_To(0) <= '1';
					when others =>
						Set_BusB_To <= "1000";
					end case;
					TStates <= "100";
				when 3 =>
					NoRead <= '1';
					ALU_Op <= "0011";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					Set_BusA_To(2 downto 0) <= "100";
					case to_integer(unsigned(IR(5 downto 4))) is
					when 0|1|2 =>
						Set_BusB_To(2 downto 1) <= IR(5 downto 4);
					when others =>
							Set_BusB_To <= "1001";
					end case;
				when others =>
				end case;
			when "01101111" =>
				-- RLD
				MCycles <= "100";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					NoRead <= '1';
					Set_Addr_To <= aXY;
				when 3 =>
					Read_To_Reg <= '1';
					Set_BusB_To(2 downto 0) <= "110";
					Set_BusA_To(2 downto 0) <= "111";
					ALU_Op <= "1101";
					TStates <= "100";
					Set_Addr_To <= aXY;
					Save_ALU <= '1';
				when 4 =>
					I_RLD <= '1';
					Write <= '1';
				when others =>
				end case;
			when "01100111" =>
				-- RRD
				MCycles <= "100";
				case to_integer(unsigned(MCycle)) is
				when 2 =>
					Set_Addr_To <= aXY;
				when 3 =>
					Read_To_Reg <= '1';
					Set_BusB_To(2 downto 0) <= "110";
					Set_BusA_To(2 downto 0) <= "111";
					ALU_Op <= "1110";
					TStates <= "100";
					Set_Addr_To <= aXY;
					Save_ALU <= '1';
				when 4 =>
					I_RRD <= '1';
					Write <= '1';
				when others =>
				end case;
			when "01000101"|"01001101"|"01010101"|"01011101"|"01100101"|"01101101"|"01110101"|"01111101" =>
				-- RETI, RETN
				MCycles <= "011";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_TO <= aSP;
				when 2 =>
					IncDec_16 <= "0111";
					Set_Addr_To <= aSP;
					LDZ <= '1';
				when 3 =>
					Jump <= '1';
					IncDec_16 <= "0111";
					I_RETN <= '1';
				when others => null;
				end case;
			when "01000000"|"01001000"|"01010000"|"01011000"|"01100000"|"01101000"|"01110000"|"01111000" =>
				-- IN r,(C)
				MCycles <= "010";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aBC;
				when 2 =>
					IORQ <= '1';
					if IR(5 downto 3) /= "110" then
						Read_To_Reg <= '1';
						Set_BusA_To(2 downto 0) <= IR(5 downto 3);
					end if;
					I_INRC <= '1';
				when others =>
				end case;
			when "01000001"|"01001001"|"01010001"|"01011001"|"01100001"|"01101001"|"01110001"|"01111001" =>
				-- OUT (C),r
				-- OUT (C),0
				MCycles <= "010";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aBC;
					Set_BusB_To(2 downto 0)     <= IR(5 downto 3);
					if IR(5 downto 3) = "110" then
						Set_BusB_To(3) <= '1';
					end if;
				when 2 =>
					Write <= '1';
					IORQ <= '1';
				when others =>
				end case;
			when "10100010" | "10101010" | "10110010" | "10111010" =>
				-- INI, IND, INIR, INDR
				-- note B is decremented AFTER being put on the bus
				MCycles <= "100";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					Set_Addr_To <= aBC;
					Set_BusB_To <= "1010";
					Set_BusA_To <= "0000";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					ALU_Op <= "0010";
				when 2 =>
					IORQ <= '1';
					Set_BusB_To <= "0110";
					Set_Addr_To <= aXY;
				when 3 =>
					if IR(3) = '0' then
						--IncDec_16 <= "0010";
						IncDec_16 <= "0110";
					else
						--IncDec_16 <= "1010";
						IncDec_16 <= "1110";
					end if;
					TStates <= "100";
					Write <= '1';
					I_BTR <= '1';
				when 4 =>
					NoRead <= '1';
					TStates <= "101";
				when others => null;
				end case;
			when "10100011" | "10101011" | "10110011" | "10111011" =>
				-- OUTI, OUTD, OTIR, OTDR
				-- note B is decremented BEFORE being put on the bus.
				-- mikej fix for hl inc
				MCycles <= "100";
				case to_integer(unsigned(MCycle)) is
				when 1 =>
					TStates <= "101";
					Set_Addr_To <= aXY;
					Set_BusB_To <= "1010";
					Set_BusA_To <= "0000";
					Read_To_Reg <= '1';
					Save_ALU <= '1';
					ALU_Op <= "0010";
				when 2 =>
					Set_BusB_To <= "0110";
					Set_Addr_To <= aBC;
				when 3 =>
					if IR(3) = '0' then
						IncDec_16 <= "0110"; -- mikej
					else
						IncDec_16 <= "1110"; -- mikej
					end if;
					IORQ <= '1';
					Write <= '1';
					I_BTR <= '1';
				when 4 =>
					NoRead <= '1';
					TStates <= "101";
				when others => null;
				end case;
			end case;

		end case;

		if Mode = 1 then
			if MCycle = "001" then
--              TStates <= "100";
			else
				TStates <= "011";
			end if;
		end if;

		if Mode = 3 then
			if MCycle = "001" then
--              TStates <= "100";
			else
				TStates <= "100";
			end if;
		end if;

		if Mode < 2 then
			if MCycle = "110" then
				Inc_PC <= '1';
				if Mode = 1 then
					Set_Addr_To <= aXY;
					TStates <= "100";
					Set_BusB_To(2 downto 0) <= SSS;
					Set_BusB_To(3) <= '0';
				end if;
				if IRB = "00110110" or IRB = "11001011" then
					Set_Addr_To <= aNone;
				end if;
			end if;
			if MCycle = "111" then
				if Mode = 0 then
					TStates <= "101";
				end if;
				if ISet /= "01" then
					Set_Addr_To <= aXY;
				end if;
				Set_BusB_To(2 downto 0) <= SSS;
				Set_BusB_To(3) <= '0';
				if IRB = "00110110" or ISet = "01" then
					-- LD (HL),n
					Inc_PC <= '1';
				else
					NoRead <= '1';
				end if;
			end if;
		end if;

	end process;

end;