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//
// TV80 8-Bit Microprocessor Core
// Based on the VHDL T80 core by Daniel Wallner (jesus@opencores.org)
//
// Copyright (c) 2004 Guy Hutchison (ghutchis@opencores.org)
//
// Permission is hereby granted, free of charge, to any person obtaining a 
// copy of this software and associated documentation files (the "Software"), 
// to deal in the Software without restriction, including without limitation 
// the rights to use, copy, modify, merge, publish, distribute, sublicense, 
// and/or sell copies of the Software, and to permit persons to whom the 
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included 
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY 
// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE 
// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
module tv80_core (/*AUTOARG*/
  // Outputs
  m1_n, iorq, no_read, write, rfsh_n, halt_n, busak_n, A, dout, mc,
  ts, intcycle_n, IntE, stop,
  // Inputs
  reset_n, clk, cen, wait_n, int_n, nmi_n, busrq_n, dinst, di
  );
  // Beginning of automatic inputs (from unused autoinst inputs)
  // End of automatics
 
  parameter Mode = 1;   // 0 => Z80, 1 => Fast Z80, 2 => 8080, 3 => GB
  parameter IOWait = 1; // 0 => Single cycle I/O, 1 => Std I/O cycle
  parameter Flag_C = 0;
  parameter Flag_N = 1;
  parameter Flag_P = 2;
  parameter Flag_X = 3;
  parameter Flag_H = 4;
  parameter Flag_Y = 5;
  parameter Flag_Z = 6;
  parameter Flag_S = 7;
 
  input     reset_n;            
  input     clk;                
  input     cen;                
  input     wait_n;             
  input     int_n;              
  input     nmi_n;              
  input     busrq_n;            
  output    m1_n;               
  output    iorq;               
  output    no_read;            
  output    write;              
  output    rfsh_n;             
  output    halt_n;             
  output    busak_n;            
  output [15:0] A; 
  input [7:0]   dinst;  
  input [7:0]   di;     
  output [7:0]  dout;     
  output [6:0]  mc;     
  output [6:0]  ts;     
  output        intcycle_n;     
  output        IntE;           
  output        stop;           
 
  reg    m1_n;          
  reg    iorq; 
`ifdef TV80_REFRESH         
  reg    rfsh_n;   
`endif             
  reg    halt_n;                
  reg    busak_n;               
  reg [15:0] A; 
  reg [7:0]  dout;        
  reg [6:0]  mc;        
  reg [6:0]  ts;        
  reg   intcycle_n;     
  reg   IntE;           
  reg   stop;           
 
  parameter     aNone    = 3'b111;
  parameter     aBC      = 3'b000;
  parameter     aDE      = 3'b001;
  parameter     aXY      = 3'b010;
  parameter     aIOA     = 3'b100;
  parameter     aSP      = 3'b101;
  parameter     aZI      = 3'b110;
 
  // Registers
  reg [7:0]     ACC, F;
  reg [7:0]     Ap, Fp;
  reg [7:0]     I;
`ifdef TV80_REFRESH
  reg [7:0]     R;
`endif
  reg [15:0]    SP, PC;
  reg [7:0]     RegDIH;
  reg [7:0]     RegDIL;
  wire [15:0]   RegBusA;
  wire [15:0]   RegBusB;
  wire [15:0]   RegBusC;
  reg [2:0]     RegAddrA_r;
  reg [2:0]     RegAddrA;
  reg [2:0]     RegAddrB_r;
  reg [2:0]     RegAddrB;
  reg [2:0]     RegAddrC;
  reg           RegWEH;
  reg           RegWEL;
  reg           Alternate;
 
  // Help Registers
  reg [15:0]    TmpAddr;        // Temporary address register
  reg [7:0]     IR;             // Instruction register
  reg [1:0]     ISet;           // Instruction set selector
  reg [15:0]    RegBusA_r;
 
  reg [15:0]    ID16;
  reg [7:0]     Save_Mux;
 
  reg [6:0]     tstate;
  reg [6:0]     mcycle;
  reg           last_mcycle, last_tstate;
  reg           IntE_FF1;
  reg           IntE_FF2;
  reg           Halt_FF;
  reg           BusReq_s;
  reg           BusAck;
  reg           ClkEn;
  reg           NMI_s;
  reg           INT_s;
  reg [1:0]     IStatus;
 
  reg [7:0]     DI_Reg;
  reg           T_Res;
  reg [1:0]     XY_State;
  reg [2:0]     Pre_XY_F_M;
  reg           NextIs_XY_Fetch;
  reg           XY_Ind;
  reg           No_BTR;
  reg           BTR_r;
  reg           Auto_Wait;
  reg           Auto_Wait_t1;
  reg           Auto_Wait_t2;
  reg           IncDecZ;
 
  // ALU signals
  reg [7:0]     BusB;
  reg [7:0]     BusA;
  wire [7:0]    ALU_Q;
  wire [7:0]    F_Out;
 
  // Registered micro code outputs
  reg [4:0]     Read_To_Reg_r;
  reg           Arith16_r;
  reg           Z16_r;
  reg [3:0]     ALU_Op_r;
  reg           Save_ALU_r;
  reg           PreserveC_r;
  reg [2:0]     mcycles;
 
  // Micro code outputs
  wire [2:0]    mcycles_d;
  wire [2:0]    tstates;
  reg           IntCycle;
  reg           NMICycle;
  wire          Inc_PC;
  wire          Inc_WZ;
  wire [3:0]    IncDec_16;
  wire [1:0]    Prefix;
  wire          Read_To_Acc;
  wire          Read_To_Reg;
  wire [3:0]     Set_BusB_To;
  wire [3:0]     Set_BusA_To;
  wire [3:0]     ALU_Op;
  wire           Save_ALU;
  wire           PreserveC;
  wire           Arith16;
  wire [2:0]     Set_Addr_To;
  wire           Jump;
  wire           JumpE;
  wire           JumpXY;
  wire           Call;
  wire           RstP;
  wire           LDZ;
  wire           LDW;
  wire           LDSPHL;
  wire           iorq_i;
  wire [2:0]     Special_LD;
  wire           ExchangeDH;
  wire           ExchangeRp;
  wire           ExchangeAF;
  wire           ExchangeRS;
  wire           I_DJNZ;
  wire           I_CPL;
  wire           I_CCF;
  wire           I_SCF;
  wire           I_RETN;
  wire           I_BT;
  wire           I_BC;
  wire           I_BTR;
  wire           I_RLD;
  wire           I_RRD;
  wire           I_INRC;
  wire           SetDI;
  wire           SetEI;
  wire [1:0]     IMode;
  wire           Halt;
 
  reg [15:0]     PC16;
  reg [15:0]     PC16_B;
  reg [15:0]     SP16, SP16_A, SP16_B;
  reg [15:0]     ID16_B;
  reg            Oldnmi_n;
 
  tv80_mcode #(Mode, Flag_C, Flag_N, Flag_P, Flag_X, Flag_H, Flag_Y, Flag_Z, Flag_S) i_mcode
    (
     .IR                   (IR),
     .ISet                 (ISet),
     .MCycle               (mcycle),
     .F                    (F),
     .NMICycle             (NMICycle),
     .IntCycle             (IntCycle),
     .MCycles              (mcycles_d),
     .TStates              (tstates),
     .Prefix               (Prefix),
     .Inc_PC               (Inc_PC),
     .Inc_WZ               (Inc_WZ),
     .IncDec_16            (IncDec_16),
     .Read_To_Acc          (Read_To_Acc),
     .Read_To_Reg          (Read_To_Reg),
     .Set_BusB_To          (Set_BusB_To),
     .Set_BusA_To          (Set_BusA_To),
     .ALU_Op               (ALU_Op),
     .Save_ALU             (Save_ALU),
     .PreserveC            (PreserveC),
     .Arith16              (Arith16),
     .Set_Addr_To          (Set_Addr_To),
     .IORQ                 (iorq_i),
     .Jump                 (Jump),
     .JumpE                (JumpE),
     .JumpXY               (JumpXY),
     .Call                 (Call),
     .RstP                 (RstP),
     .LDZ                  (LDZ),
     .LDW                  (LDW),
     .LDSPHL               (LDSPHL),
     .Special_LD           (Special_LD),
     .ExchangeDH           (ExchangeDH),
     .ExchangeRp           (ExchangeRp),
     .ExchangeAF           (ExchangeAF),
     .ExchangeRS           (ExchangeRS),
     .I_DJNZ               (I_DJNZ),
     .I_CPL                (I_CPL),
     .I_CCF                (I_CCF),
     .I_SCF                (I_SCF),
     .I_RETN               (I_RETN),
     .I_BT                 (I_BT),
     .I_BC                 (I_BC),
     .I_BTR                (I_BTR),
     .I_RLD                (I_RLD),
     .I_RRD                (I_RRD),
     .I_INRC               (I_INRC),
     .SetDI                (SetDI),
     .SetEI                (SetEI),
     .IMode                (IMode),
     .Halt                 (Halt),
     .NoRead               (no_read),
     .Write                (write)
     );
 
  tv80_alu #(Mode, Flag_C, Flag_N, Flag_P, Flag_X, Flag_H, Flag_Y, Flag_Z, Flag_S) i_alu
    (
     .Arith16              (Arith16_r),
     .Z16                  (Z16_r),
     .ALU_Op               (ALU_Op_r),
     .IR                   (IR[5:0]),
     .ISet                 (ISet),
     .BusA                 (BusA),
     .BusB                 (BusB),
     .F_In                 (F),
     .Q                    (ALU_Q),
     .F_Out                (F_Out)
     );
 
  function [6:0] number_to_bitvec;
    input [2:0] num;
    begin
      case (num)
        1 : number_to_bitvec = 7'b0000001;
        2 : number_to_bitvec = 7'b0000010;
        3 : number_to_bitvec = 7'b0000100;
        4 : number_to_bitvec = 7'b0001000;
        5 : number_to_bitvec = 7'b0010000;
        6 : number_to_bitvec = 7'b0100000;
        7 : number_to_bitvec = 7'b1000000;
        default : number_to_bitvec = 7'bx;
      endcase // case(num)
    end
  endfunction // number_to_bitvec
 
  function [2:0] mcyc_to_number;
    input [6:0] mcyc;
    begin
      casez (mcyc)
        7'b1zzzzzz : mcyc_to_number = 3'h7;
        7'b01zzzzz : mcyc_to_number = 3'h6;
        7'b001zzzz : mcyc_to_number = 3'h5;
        7'b0001zzz : mcyc_to_number = 3'h4;
        7'b00001zz : mcyc_to_number = 3'h3;
        7'b000001z : mcyc_to_number = 3'h2;
        7'b0000001 : mcyc_to_number = 3'h1;
        default : mcyc_to_number = 3'h1;
      endcase
    end
  endfunction
 
  always @(/*AUTOSENSE*/mcycle or mcycles or tstate or tstates)
    begin
      case (mcycles)
        1 : last_mcycle = mcycle[0];
        2 : last_mcycle = mcycle[1];
        3 : last_mcycle = mcycle[2];
        4 : last_mcycle = mcycle[3];
        5 : last_mcycle = mcycle[4];
        6 : last_mcycle = mcycle[5];
        7 : last_mcycle = mcycle[6];
        default : last_mcycle = 1'bx;
      endcase // case(mcycles)
 
      case (tstates)
        0 : last_tstate = tstate[0];
        1 : last_tstate = tstate[1];
        2 : last_tstate = tstate[2];
        3 : last_tstate = tstate[3];
        4 : last_tstate = tstate[4];
        5 : last_tstate = tstate[5];
        6 : last_tstate = tstate[6];
        default : last_tstate = 1'bx;
      endcase
    end // always @ (...
 
 
  always @(/*AUTOSENSE*/ALU_Q or BusAck or BusB or DI_Reg
	   or ExchangeRp or IR or Save_ALU_r or Set_Addr_To or XY_Ind
	   or XY_State or cen or last_tstate or mcycle)
    begin
      ClkEn = cen && ~ BusAck;
 
      if (last_tstate)
        T_Res = 1'b1;
      else T_Res = 1'b0;
 
      if (XY_State != 2'b00 && XY_Ind == 1'b0 &&
          ((Set_Addr_To == aXY) ||
           (mcycle[0] && IR == 8'b11001011) ||
           (mcycle[0] && IR == 8'b00110110)))
        NextIs_XY_Fetch = 1'b1;
      else 
        NextIs_XY_Fetch = 1'b0;
 
      if (ExchangeRp)
        Save_Mux = BusB;
      else if (!Save_ALU_r)
        Save_Mux = DI_Reg;
      else
        Save_Mux = ALU_Q;
    end // always @ *
 
  always @ (posedge clk or negedge reset_n)
    begin
      if (reset_n == 1'b0 ) 
        begin
          PC <= #1 0;  // Program Counter
          A <= #1 0;
          TmpAddr <= #1 0;
          IR <= #1 8'b00000000;
          ISet <= #1 2'b00;
          XY_State <= #1 2'b00;
          IStatus <= #1 2'b00;
          mcycles <= #1 3'b000;
          dout <= #1 8'b00000000;
 
          ACC <= #1 8'hFF;
          F <= #1 8'hFF;
          Ap <= #1 8'hFF;
          Fp <= #1 8'hFF;
          I <= #1 0;
          `ifdef TV80_REFRESH
          R <= #1 0;
          `endif
          SP <= #1 16'hFFFF;
          Alternate <= #1 1'b0;
 
          Read_To_Reg_r <= #1 5'b00000;
          Arith16_r <= #1 1'b0;
          BTR_r <= #1 1'b0;
          Z16_r <= #1 1'b0;
          ALU_Op_r <= #1 4'b0000;
          Save_ALU_r <= #1 1'b0;
          PreserveC_r <= #1 1'b0;
          XY_Ind <= #1 1'b0;
        end 
      else 
        begin
 
          if (ClkEn == 1'b1 ) 
            begin
 
              ALU_Op_r <= #1 4'b0000;
              Save_ALU_r <= #1 1'b0;
              Read_To_Reg_r <= #1 5'b00000;
 
              mcycles <= #1 mcycles_d;
 
              if (IMode != 2'b11 ) 
                begin
                  IStatus <= #1 IMode;
                end
 
              Arith16_r <= #1 Arith16;
              PreserveC_r <= #1 PreserveC;
              if (ISet == 2'b10 && ALU_Op[2] == 1'b0 && ALU_Op[0] == 1'b1 && mcycle[2] ) 
                begin
                  Z16_r <= #1 1'b1;
                end 
              else 
                begin
                  Z16_r <= #1 1'b0;
                end
 
              if (mcycle[0] && (tstate[1] | tstate[2] | tstate[3] )) 
                begin
                  // mcycle == 1 && tstate == 1, 2, || 3
                  if (tstate[2] && wait_n == 1'b1 ) 
                    begin
                      `ifdef TV80_REFRESH
                      if (Mode < 2 ) 
                        begin
                          A[7:0] <= #1 R;
                          A[15:8] <= #1 I;
                          R[6:0] <= #1 R[6:0] + 1;
                        end
                      `endif
                      if (Jump == 1'b0 && Call == 1'b0 && NMICycle == 1'b0 && IntCycle == 1'b0 && ~ (Halt_FF == 1'b1 || Halt == 1'b1) ) 
                        begin
                          PC <= #1 PC16;
                        end
 
                      if (IntCycle == 1'b1 && IStatus == 2'b01 ) 
                        begin
                          IR <= #1 8'b11111111;
                        end 
                      else if (Halt_FF == 1'b1 || (IntCycle == 1'b1 && IStatus == 2'b10) || NMICycle == 1'b1 ) 
                        begin
                          IR <= #1 8'b00000000;
			  TmpAddr[7:0] <= #1 dinst; // Special M1 vector fetch
                        end 
                      else 
                        begin
                          IR <= #1 dinst;
                        end
 
                      ISet <= #1 2'b00;
                      if (Prefix != 2'b00 ) 
                        begin
                          if (Prefix == 2'b11 ) 
                            begin
                              if (IR[5] == 1'b1 ) 
                                begin
                                  XY_State <= #1 2'b10;
                                end 
                              else 
                                begin
                                  XY_State <= #1 2'b01;
                                end
                            end 
                          else 
                            begin
                              if (Prefix == 2'b10 ) 
                                begin
                                  XY_State <= #1 2'b00;
                                  XY_Ind <= #1 1'b0;
                                end
                              ISet <= #1 Prefix;
                            end
                        end 
                      else 
                        begin
                          XY_State <= #1 2'b00;
                          XY_Ind <= #1 1'b0;
                        end
                    end // if (tstate == 2 && wait_n == 1'b1 )
 
 
                end 
              else 
                begin
                  // either (mcycle > 1) OR (mcycle == 1 AND tstate > 3)
 
                  if (mcycle[5] ) 
                    begin
                      XY_Ind <= #1 1'b1;
                      if (Prefix == 2'b01 ) 
                        begin
                          ISet <= #1 2'b01;
                        end
                    end
 
                  if (T_Res == 1'b1 ) 
                    begin
                      BTR_r <= #1 (I_BT || I_BC || I_BTR) && ~ No_BTR;
                      if (Jump == 1'b1 ) 
                        begin
                          A[15:8] <= #1 DI_Reg;
                          A[7:0] <= #1 TmpAddr[7:0];
                          PC[15:8] <= #1 DI_Reg;
                          PC[7:0] <= #1 TmpAddr[7:0];
                        end 
                      else if (JumpXY == 1'b1 ) 
                        begin
                          A <= #1 RegBusC;
                          PC <= #1 RegBusC;
                        end else if (Call == 1'b1 || RstP == 1'b1 ) 
                          begin
                            A <= #1 TmpAddr;
                            PC <= #1 TmpAddr;
                          end 
                        else if (last_mcycle && NMICycle == 1'b1 ) 
                          begin
                            A <= #1 16'b0000000001100110;
                            PC <= #1 16'b0000000001100110;
                          end 
                        else if (mcycle[2] && IntCycle == 1'b1 && IStatus == 2'b10 ) 
                          begin
                            A[15:8] <= #1 I;
                            A[7:0] <= #1 TmpAddr[7:0];
                            PC[15:8] <= #1 I;
                            PC[7:0] <= #1 TmpAddr[7:0];
                          end 
                        else 
                          begin
                            case (Set_Addr_To)
                              aXY :
                                begin
                                  if (XY_State == 2'b00 ) 
                                    begin
                                      A <= #1 RegBusC;
                                    end 
                                  else 
                                    begin
                                      if (NextIs_XY_Fetch == 1'b1 )
                                        begin
                                          A <= #1 PC;
                                        end 
                                      else 
                                        begin
                                          A <= #1 TmpAddr;
                                        end
                                    end // else: !if(XY_State == 2'b00 )
                                end // case: aXY
 
                              aIOA :
                                begin
                                  if (Mode == 3 ) 
                                    begin
                                      // Memory map I/O on GBZ80
                                      A[15:8] <= #1 8'hFF;
                                    end 
                                  else if (Mode == 2 ) 
                                    begin
                                      // Duplicate I/O address on 8080
                                      A[15:8] <= #1 DI_Reg;
                                    end 
                                  else 
                                    begin
                                      A[15:8] <= #1 ACC;
                                    end
                                  A[7:0] <= #1 DI_Reg;
                                end // case: aIOA
 
 
                              aSP :
                                begin
                                  A <= #1 SP;
                                end
 
                              aBC :
                                begin
                                  if (Mode == 3 && iorq_i == 1'b1 ) 
                                    begin
                                      // Memory map I/O on GBZ80
                                      A[15:8] <= #1 8'hFF;
                                      A[7:0] <= #1 RegBusC[7:0];
                                    end 
                                  else 
                                    begin
                                      A <= #1 RegBusC;
                                    end
                                end // case: aBC
 
                              aDE :
                                begin
                                  A <= #1 RegBusC;
                                end
 
                              aZI :
                                begin                                  
                                  if (Inc_WZ == 1'b1 ) 
                                    begin
                                      A <= #1 TmpAddr + 1;
                                    end 
                                  else 
                                    begin
                                      A[15:8] <= #1 DI_Reg;
                                      A[7:0] <= #1 TmpAddr[7:0];
                                    end
                                end // case: aZI
 
                              default   :
                                begin                                    
                                  A <= #1 PC;
                                end
                            endcase // case(Set_Addr_To)
 
                          end // else: !if(mcycle[2] && IntCycle == 1'b1 && IStatus == 2'b10 )
 
 
                      Save_ALU_r <= #1 Save_ALU;
                      ALU_Op_r <= #1 ALU_Op;
 
                      if (I_CPL == 1'b1 ) 
                        begin
                          // CPL
                          ACC <= #1 ~ ACC;
                          F[Flag_Y] <= #1 ~ ACC[5];
                          F[Flag_H] <= #1 1'b1;
                          F[Flag_X] <= #1 ~ ACC[3];
                          F[Flag_N] <= #1 1'b1;
                        end
                      if (I_CCF == 1'b1 ) 
                        begin
                          // CCF
                          F[Flag_C] <= #1 ~ F[Flag_C];
                          F[Flag_Y] <= #1 ACC[5];
                          F[Flag_H] <= #1 F[Flag_C];
                          F[Flag_X] <= #1 ACC[3];
                          F[Flag_N] <= #1 1'b0;
                        end
                      if (I_SCF == 1'b1 ) 
                        begin
                          // SCF
                          F[Flag_C] <= #1 1'b1;
                          F[Flag_Y] <= #1 ACC[5];
                          F[Flag_H] <= #1 1'b0;
                          F[Flag_X] <= #1 ACC[3];
                          F[Flag_N] <= #1 1'b0;
                        end
                    end // if (T_Res == 1'b1 )
 
 
                  if (tstate[2] && wait_n == 1'b1 ) 
                    begin
                      if (ISet == 2'b01 && mcycle[6] ) 
                        begin
                          IR <= #1 dinst;
                        end
                      if (JumpE == 1'b1 ) 
                        begin
                          PC <= #1 PC16;
                        end 
                      else if (Inc_PC == 1'b1 ) 
                        begin
                          //PC <= #1 PC + 1;
                          PC <= #1 PC16;
                        end
                      if (BTR_r == 1'b1 ) 
                        begin
                          //PC <= #1 PC - 2;
                          PC <= #1 PC16;
                        end
                      if (RstP == 1'b1 ) 
                        begin
                          TmpAddr <= #1 { 10'h0, IR[5:3], 3'h0 };
                          //TmpAddr <= #1 (others =>1'b0);
                          //TmpAddr[5:3] <= #1 IR[5:3];
                        end
                    end
                  if (tstate[3] && mcycle[5] ) 
                    begin
                      TmpAddr <= #1 SP16;
                    end
 
                  if ((tstate[2] && wait_n == 1'b1) || (tstate[4] && mcycle[0]) ) 
                    begin
                      if (IncDec_16[2:0] == 3'b111 ) 
                        begin
                          SP <= #1 SP16;
                        end
                    end
 
                  if (LDSPHL == 1'b1 ) 
                    begin
                      SP <= #1 RegBusC;
                    end
                  if (ExchangeAF == 1'b1 ) 
                    begin
                      Ap <= #1 ACC;
                      ACC <= #1 Ap;
                      Fp <= #1 F;
                      F <= #1 Fp;
                    end
                  if (ExchangeRS == 1'b1 ) 
                    begin
                      Alternate <= #1 ~ Alternate;
                    end
                end // else: !if(mcycle  == 3'b001 && tstate(2) == 1'b0 )
 
 
              if (tstate[3] ) 
                begin
                  if (LDZ == 1'b1 ) 
                    begin
                      TmpAddr[7:0] <= #1 DI_Reg;
                    end
                  if (LDW == 1'b1 ) 
                    begin
                      TmpAddr[15:8] <= #1 DI_Reg;
                    end
 
                  if (Special_LD[2] == 1'b1 ) 
                    begin
                      case (Special_LD[1:0])
                        2'b00 :
                          begin
                            ACC <= #1 I;
                            F[Flag_P] <= #1 IntE_FF2;
			    F[Flag_Z] <= (I == 0);
			    F[Flag_S] <= I[7];
			    F[Flag_H] <= 0;
			    F[Flag_N] <= 0; 
                          end
 
                        2'b01 :
                          begin
                            `ifdef TV80_REFRESH
                            ACC <= #1 R;
                            `else
                            ACC <= #1 0;
                            `endif
                            F[Flag_P] <= #1 IntE_FF2;
			    F[Flag_Z] <= (I == 0);
			    F[Flag_S] <= I[7];
			    F[Flag_H] <= 0;
			    F[Flag_N] <= 0; 
                          end
 
                        2'b10 :
                          I <= #1 ACC;
 
                        `ifdef TV80_REFRESH                        
                        default :
                          R <= #1 ACC;
                        `else
                        default : ;
                        `endif                        
                      endcase
                    end
                end // if (tstate == 3 )
 
 
              if ((I_DJNZ == 1'b0 && Save_ALU_r == 1'b1) || ALU_Op_r == 4'b1001 ) 
                begin
                  if (Mode == 3 ) 
                    begin
                      F[6] <= #1 F_Out[6];
                      F[5] <= #1 F_Out[5];
                      F[7] <= #1 F_Out[7];
                      if (PreserveC_r == 1'b0 ) 
                        begin
                          F[4] <= #1 F_Out[4];
                        end
                    end 
                  else 
                    begin
                      F[7:1] <= #1 F_Out[7:1];
                      if (PreserveC_r == 1'b0 ) 
                        begin
                          F[Flag_C] <= #1 F_Out[0];
                        end
                    end
                end // if ((I_DJNZ == 1'b0 && Save_ALU_r == 1'b1) || ALU_Op_r == 4'b1001 )
 
              if (T_Res == 1'b1 && I_INRC == 1'b1 ) 
                begin
                  F[Flag_H] <= #1 1'b0;
                  F[Flag_N] <= #1 1'b0;
                  if (DI_Reg[7:0] == 8'b00000000 ) 
                    begin
                      F[Flag_Z] <= #1 1'b1;
                    end 
                  else 
                    begin
                      F[Flag_Z] <= #1 1'b0;
                    end
                  F[Flag_S] <= #1 DI_Reg[7];
                  F[Flag_P] <= #1 ~ (^DI_Reg[7:0]);
                end // if (T_Res == 1'b1 && I_INRC == 1'b1 )
 
 
              if (tstate[1] && Auto_Wait_t1 == 1'b0 ) 
                begin
                  dout <= #1 BusB;
                  if (I_RLD == 1'b1 ) 
                    begin
                      dout[3:0] <= #1 BusA[3:0];
                      dout[7:4] <= #1 BusB[3:0];
                    end
                  if (I_RRD == 1'b1 ) 
                    begin
                      dout[3:0] <= #1 BusB[7:4];
                      dout[7:4] <= #1 BusA[3:0];
                    end
                end
 
              if (T_Res == 1'b1 ) 
                begin
                  Read_To_Reg_r[3:0] <= #1 Set_BusA_To;
                  Read_To_Reg_r[4] <= #1 Read_To_Reg;
                  if (Read_To_Acc == 1'b1 ) 
                    begin
                      Read_To_Reg_r[3:0] <= #1 4'b0111;
                      Read_To_Reg_r[4] <= #1 1'b1;
                    end
                end
 
              if (tstate[1] && I_BT == 1'b1 ) 
                begin
                  F[Flag_X] <= #1 ALU_Q[3];
                  F[Flag_Y] <= #1 ALU_Q[1];
                  F[Flag_H] <= #1 1'b0;
                  F[Flag_N] <= #1 1'b0;
                end
              if (I_BC == 1'b1 || I_BT == 1'b1 ) 
                begin
                  F[Flag_P] <= #1 IncDecZ;
                end
 
              if ((tstate[1] && Save_ALU_r == 1'b0 && Auto_Wait_t1 == 1'b0) ||
                  (Save_ALU_r == 1'b1 && ALU_Op_r != 4'b0111) ) 
                begin
                  case (Read_To_Reg_r)
                    5'b10111 :
                      ACC <= #1 Save_Mux;
                    5'b10110 :
                      dout <= #1 Save_Mux;
                    5'b11000 :
                      SP[7:0] <= #1 Save_Mux;
                    5'b11001 :
                      SP[15:8] <= #1 Save_Mux;
                    5'b11011 :
                      F <= #1 Save_Mux;
                    default : ;
                  endcase
                end // if ((tstate == 1 && Save_ALU_r == 1'b0 && Auto_Wait_t1 == 1'b0) ||...              
            end // if (ClkEn == 1'b1 )         
        end // else: !if(reset_n == 1'b0 )
    end
 
 
  //-------------------------------------------------------------------------
  //
  // BC('), DE('), HL('), IX && IY
  //
  //-------------------------------------------------------------------------
  always @ (posedge clk)
    begin
      if (ClkEn == 1'b1 ) 
        begin
          // Bus A / Write
          RegAddrA_r <= #1  { Alternate, Set_BusA_To[2:1] };
          if (XY_Ind == 1'b0 && XY_State != 2'b00 && Set_BusA_To[2:1] == 2'b10 ) 
            begin
              RegAddrA_r <= #1 { XY_State[1],  2'b11 };
            end
 
          // Bus B
          RegAddrB_r <= #1 { Alternate, Set_BusB_To[2:1] };
          if (XY_Ind == 1'b0 && XY_State != 2'b00 && Set_BusB_To[2:1] == 2'b10 ) 
            begin
              RegAddrB_r <= #1 { XY_State[1],  2'b11 };
            end
 
          // Address from register
          RegAddrC <= #1 { Alternate,  Set_Addr_To[1:0] };
          // Jump (HL), LD SP,HL
          if ((JumpXY == 1'b1 || LDSPHL == 1'b1) ) 
            begin
              RegAddrC <= #1 { Alternate, 2'b10 };
            end
          if (((JumpXY == 1'b1 || LDSPHL == 1'b1) && XY_State != 2'b00) || (mcycle[5]) ) 
            begin
              RegAddrC <= #1 { XY_State[1],  2'b11 };
            end
 
          if (I_DJNZ == 1'b1 && Save_ALU_r == 1'b1 && Mode < 2 ) 
            begin
              IncDecZ <= #1 F_Out[Flag_Z];
            end
          if ((tstate[2] || (tstate[3] && mcycle[0])) && IncDec_16[2:0] == 3'b100 ) 
            begin
              if (ID16 == 0 ) 
                begin
                  IncDecZ <= #1 1'b0;
                end 
              else 
                begin
                  IncDecZ <= #1 1'b1;
                end
            end
 
          RegBusA_r <= #1 RegBusA;
        end
 
    end // always @ (posedge clk)
 
 
  always @(/*AUTOSENSE*/Alternate or ExchangeDH or IncDec_16
	   or RegAddrA_r or RegAddrB_r or XY_State or mcycle or tstate)
    begin
      if ((tstate[2] || (tstate[3] && mcycle[0] && IncDec_16[2] == 1'b1)) && XY_State == 2'b00)
        RegAddrA = { Alternate, IncDec_16[1:0] };
      else if ((tstate[2] || (tstate[3] && mcycle[0] && IncDec_16[2] == 1'b1)) && IncDec_16[1:0] == 2'b10)
        RegAddrA = { XY_State[1], 2'b11 };
      else if (ExchangeDH == 1'b1 && tstate[3])
        RegAddrA = { Alternate, 2'b10 };
      else if (ExchangeDH == 1'b1 && tstate[4])
        RegAddrA = { Alternate, 2'b01 };
      else
        RegAddrA = RegAddrA_r;
 
      if (ExchangeDH == 1'b1 && tstate[3])
        RegAddrB = { Alternate, 2'b01 };
      else
        RegAddrB = RegAddrB_r;
    end // always @ *
 
 
  always @(/*AUTOSENSE*/ALU_Op_r or Auto_Wait_t1 or ExchangeDH
	   or IncDec_16 or Read_To_Reg_r or Save_ALU_r or mcycle
	   or tstate or wait_n)
    begin
      RegWEH = 1'b0;
      RegWEL = 1'b0;
      if ((tstate[1] && Save_ALU_r == 1'b0 && Auto_Wait_t1 == 1'b0) ||
          (Save_ALU_r == 1'b1 && ALU_Op_r != 4'b0111) ) 
        begin
          case (Read_To_Reg_r)
            5'b10000 , 5'b10001 , 5'b10010 , 5'b10011 , 5'b10100 , 5'b10101 :
              begin
                RegWEH = ~ Read_To_Reg_r[0];
                RegWEL = Read_To_Reg_r[0];
              end // UNMATCHED !!
            default : ;
          endcase // case(Read_To_Reg_r)
 
        end // if ((tstate == 1 && Save_ALU_r == 1'b0 && Auto_Wait_t1 == 1'b0) ||...
 
 
      if (ExchangeDH == 1'b1 && (tstate[3] || tstate[4]) ) 
        begin
          RegWEH = 1'b1;
          RegWEL = 1'b1;
        end
 
      if (IncDec_16[2] && ((tstate[2] && ~wait_n && ~mcycle[0]) || (tstate[3] && mcycle[0])) ) 
        begin
          case (IncDec_16[1:0])
            2'b00 , 2'b01 , 2'b10 :
              begin
                RegWEH = 1'b1;
                RegWEL = 1'b1;
              end // UNMATCHED !!
            default : ;
          endcase
        end
    end // always @ *
 
 
  always @(/*AUTOSENSE*/ExchangeDH or ID16 or IncDec_16 or RegBusA_r
	   or RegBusB or Save_Mux or mcycle or tstate)
    begin
      RegDIH = Save_Mux;
      RegDIL = Save_Mux;
 
      if (ExchangeDH == 1'b1 && tstate[3] ) 
        begin
          RegDIH = RegBusB[15:8];
          RegDIL = RegBusB[7:0];
        end
      else if (ExchangeDH == 1'b1 && tstate[4] ) 
        begin
          RegDIH = RegBusA_r[15:8];
          RegDIL = RegBusA_r[7:0];
        end
      else if (IncDec_16[2] == 1'b1 && ((tstate[2] && ~mcycle[0]) || (tstate[3] && mcycle[0])) ) 
        begin
          RegDIH = ID16[15:8];
          RegDIL = ID16[7:0];
        end
    end
 
  tv80_reg i_reg
    (
     .clk                  (clk),
     .CEN                  (ClkEn),
     .WEH                  (RegWEH),
     .WEL                  (RegWEL),
     .AddrA                (RegAddrA),
     .AddrB                (RegAddrB),
     .AddrC                (RegAddrC),
     .DIH                  (RegDIH),
     .DIL                  (RegDIL),
     .DOAH                 (RegBusA[15:8]),
     .DOAL                 (RegBusA[7:0]),
     .DOBH                 (RegBusB[15:8]),
     .DOBL                 (RegBusB[7:0]),
     .DOCH                 (RegBusC[15:8]),
     .DOCL                 (RegBusC[7:0])
     );
 
  //-------------------------------------------------------------------------
  //
  // Buses
  //
  //-------------------------------------------------------------------------
 
  always @ (posedge clk)
    begin
      if (ClkEn == 1'b1 ) 
        begin
          case (Set_BusB_To)
            4'b0111 :
              BusB <= #1 ACC;
            4'b0000 , 4'b0001 , 4'b0010 , 4'b0011 , 4'b0100 , 4'b0101 :
              begin
                if (Set_BusB_To[0] == 1'b1 ) 
                  begin
                    BusB <= #1 RegBusB[7:0];
                  end 
                else 
                  begin
                    BusB <= #1 RegBusB[15:8];
                  end
              end
            4'b0110 :
              BusB <= #1 DI_Reg;
            4'b1000 :
              BusB <= #1 SP[7:0];
            4'b1001 :
              BusB <= #1 SP[15:8];
            4'b1010 :
              BusB <= #1 8'b00000001;
            4'b1011 :
              BusB <= #1 F;
            4'b1100 :
              BusB <= #1 PC[7:0];
            4'b1101 :
              BusB <= #1 PC[15:8];
            4'b1110 :
              BusB <= #1 8'b00000000;
            default :
              BusB <= #1 8'h0;
          endcase
 
          case (Set_BusA_To)
            4'b0111 :
              BusA <= #1 ACC;
            4'b0000 , 4'b0001 , 4'b0010 , 4'b0011 , 4'b0100 , 4'b0101 :
              begin
                if (Set_BusA_To[0] == 1'b1 )
                  begin
                    BusA <= #1 RegBusA[7:0];
                  end 
                else 
                  begin
                    BusA <= #1 RegBusA[15:8];
                  end
              end
            4'b0110 :
              BusA <= #1 DI_Reg;
            4'b1000 :
              BusA <= #1 SP[7:0];
            4'b1001 :
              BusA <= #1 SP[15:8];
            4'b1010 :
              BusA <= #1 8'b00000000;
            default :
              BusA <= #1  8'h0;
          endcase
        end
    end
 
  //-------------------------------------------------------------------------
  //
  // Generate external control signals
  //
  //-------------------------------------------------------------------------
`ifdef TV80_REFRESH
  always @ (posedge clk or negedge reset_n)
    begin
      if (reset_n == 1'b0 ) 
        begin
          rfsh_n <= #1 1'b1;
        end 
      else
        begin
          if (cen == 1'b1 ) 
            begin
              if (mcycle[0] && ((tstate[2]  && wait_n == 1'b1) || tstate[3]) ) 
                begin
                  rfsh_n <= #1 1'b0;
                end 
              else 
                begin
                  rfsh_n <= #1 1'b1;
                end
            end
        end
    end // always @ (posedge clk or negedge reset_n)
`else // !`ifdef TV80_REFRESH
  assign rfsh_n = 1'b1;
`endif  
 
  always @(/*AUTOSENSE*/BusAck or Halt_FF or I_DJNZ or IntCycle
	   or IntE_FF1 or di or iorq_i or mcycle or tstate)
    begin
      mc = mcycle;
      ts = tstate;
      DI_Reg = di;
      halt_n = ~ Halt_FF;
      busak_n = ~ BusAck;
      intcycle_n = ~ IntCycle;
      IntE = IntE_FF1;
      iorq = iorq_i;
      stop = I_DJNZ;
    end
 
  //-----------------------------------------------------------------------
  //
  // Syncronise inputs
  //
  //-----------------------------------------------------------------------
 
  always @ (posedge clk or negedge reset_n)
    begin : sync_inputs
      if (~reset_n) 
        begin
          BusReq_s <= #1 1'b0;
          INT_s <= #1 1'b0;
          NMI_s <= #1 1'b0;
          Oldnmi_n <= #1 1'b0;
        end 
      else
        begin
          if (cen == 1'b1 ) 
            begin
              BusReq_s <= #1 ~ busrq_n;
              INT_s <= #1 ~ int_n;
              if (NMICycle == 1'b1 ) 
                begin
                  NMI_s <= #1 1'b0;
                end 
              else if (nmi_n == 1'b0 && Oldnmi_n == 1'b1 ) 
                begin
                  NMI_s <= #1 1'b1;
                end
              Oldnmi_n <= #1 nmi_n;
            end
        end
    end
 
  //-----------------------------------------------------------------------
  //
  // Main state machine
  //
  //-----------------------------------------------------------------------
 
  always @ (posedge clk or negedge reset_n)
    begin
      if (reset_n == 1'b0 ) 
        begin
          mcycle <= #1 7'b0000001;
          tstate <= #1 7'b0000001;
          Pre_XY_F_M <= #1 3'b000;
          Halt_FF <= #1 1'b0;
          BusAck <= #1 1'b0;
          NMICycle <= #1 1'b0;
          IntCycle <= #1 1'b0;
          IntE_FF1 <= #1 1'b0;
          IntE_FF2 <= #1 1'b0;
          No_BTR <= #1 1'b0;
          Auto_Wait_t1 <= #1 1'b0;
          Auto_Wait_t2 <= #1 1'b0;
          m1_n <= #1 1'b1;
        end 
      else
        begin
          if (cen == 1'b1 ) 
            begin
              if (T_Res == 1'b1 ) 
                begin
                  Auto_Wait_t1 <= #1 1'b0;
                end 
              else 
                begin
		  Auto_Wait_t1 <= #1 Auto_Wait || (iorq_i & ~Auto_Wait_t2);
                end
              Auto_Wait_t2 <= #1 Auto_Wait_t1 & !T_Res;
              No_BTR <= #1 (I_BT && (~ IR[4] || ~ F[Flag_P])) ||
                        (I_BC && (~ IR[4] || F[Flag_Z] || ~ F[Flag_P])) ||
                        (I_BTR && (~ IR[4] || F[Flag_Z]));
              if (tstate[2] ) 
                begin
                  if (SetEI == 1'b1 ) 
                    begin
                      if (!NMICycle)
                        IntE_FF1 <= #1 1'b1;
                      IntE_FF2 <= #1 1'b1;
                    end
                  if (I_RETN == 1'b1 ) 
                    begin
                      IntE_FF1 <= #1 IntE_FF2;
                    end
                end
              if (tstate[3] ) 
                begin
                  if (SetDI == 1'b1 ) 
                    begin
                      IntE_FF1 <= #1 1'b0;
                      IntE_FF2 <= #1 1'b0;
                    end
                end
              if (IntCycle == 1'b1 || NMICycle == 1'b1 ) 
                begin
                  Halt_FF <= #1 1'b0;
                end
              if (mcycle[0] && tstate[2] && wait_n == 1'b1 ) 
                begin
                  m1_n <= #1 1'b1;
                end
              if (BusReq_s == 1'b1 && BusAck == 1'b1 ) 
                begin
                end 
              else 
                begin
                  BusAck <= #1 1'b0;
                  if (tstate[2] && wait_n == 1'b0 ) 
                    begin
                    end 
                  else if (T_Res == 1'b1 ) 
                    begin
                      if (Halt == 1'b1 ) 
                        begin
                          Halt_FF <= #1 1'b1;
                        end
                      if (BusReq_s == 1'b1 ) 
                        begin
                          BusAck <= #1 1'b1;
                        end 
                      else 
                        begin
                          tstate <= #1 7'b0000010;
                          if (NextIs_XY_Fetch == 1'b1 ) 
                            begin
                              mcycle <= #1 7'b0100000;
                              Pre_XY_F_M <= #1 mcyc_to_number(mcycle);
                              if (IR == 8'b00110110 && Mode == 0 ) 
                                begin
                                  Pre_XY_F_M <= #1 3'b010;
                                end
                            end 
                          else if ((mcycle[6]) || (mcycle[5] && Mode == 1 && ISet != 2'b01) ) 
                            begin
                              mcycle <= #1 number_to_bitvec(Pre_XY_F_M + 1);
                            end 
                          else if ((last_mcycle) ||
                                   No_BTR == 1'b1 ||
                                   (mcycle[1] && I_DJNZ == 1'b1 && IncDecZ == 1'b1) ) 
                            begin
                              m1_n <= #1 1'b0;
                              mcycle <= #1 7'b0000001;
                              IntCycle <= #1 1'b0;
                              NMICycle <= #1 1'b0;
                              if (NMI_s == 1'b1 && Prefix == 2'b00 ) 
                                begin
                                  NMICycle <= #1 1'b1;
                                  IntE_FF1 <= #1 1'b0;
                                end 
                              else if ((IntE_FF1 == 1'b1 && INT_s == 1'b1) && Prefix == 2'b00 && SetEI == 1'b0 ) 
                                begin
                                  IntCycle <= #1 1'b1;
                                  IntE_FF1 <= #1 1'b0;
                                  IntE_FF2 <= #1 1'b0;
                                end
                            end 
                          else 
                            begin
                              mcycle <= #1 { mcycle[5:0], mcycle[6] };
                            end
                        end
                    end 
                  else 
                    begin   // verilog has no "nor" operator
                      if ( ~(Auto_Wait == 1'b1 && Auto_Wait_t2 == 1'b0) &&
                           ~(IOWait == 1 && iorq_i == 1'b1 && Auto_Wait_t1 == 1'b0) ) 
                        begin
                          tstate <= #1 { tstate[5:0], tstate[6] };
                        end
                    end
                end
              if (tstate[0]) 
                begin
                  m1_n <= #1 1'b0;
                end
            end
        end
    end
 
  always @(/*AUTOSENSE*/BTR_r or DI_Reg or IncDec_16 or JumpE or PC
	   or RegBusA or RegBusC or SP or tstate)
    begin
      if (JumpE == 1'b1 ) 
        begin
          PC16_B = { {8{DI_Reg[7]}}, DI_Reg };
        end 
      else if (BTR_r == 1'b1 ) 
        begin
          PC16_B = -2;
        end
      else
        begin
          PC16_B = 1;
        end
 
      if (tstate[3])
        begin
          SP16_A = RegBusC;
          SP16_B = { {8{DI_Reg[7]}}, DI_Reg };
        end
      else
        begin
          // suspect that ID16 and SP16 could be shared
          SP16_A = SP;
 
          if (IncDec_16[3] == 1'b1)
            SP16_B = -1;
          else
            SP16_B = 1;
        end
 
      if (IncDec_16[3])  
        ID16_B = -1;
      else
        ID16_B = 1;
 
      ID16 = RegBusA + ID16_B;
      PC16 = PC + PC16_B;
      SP16 = SP16_A + SP16_B;
    end // always @ *
 
 
  always @(/*AUTOSENSE*/IntCycle or NMICycle or mcycle)
    begin
      Auto_Wait = 1'b0;
      if (IntCycle == 1'b1 || NMICycle == 1'b1 ) 
        begin
          if (mcycle[0] ) 
            begin
              Auto_Wait = 1'b1;
            end
        end
    end // always @ *
 
endmodule // T80