count_lut: LUT4
      --synthesis translate_off
      generic map (INIT => X"A999")
      --synthesis translate_on
      port map( I0 => stack_address(i),
                I1 => t_state,
                I2 => valid_to_move,
                I3 => call_type,
                 O => half_stack_address(i) );
    
      count_xor: XORCY
      port map( LI => half_stack_address(i),
                CI => stack_address_carry(i-1),
                 O => next_stack_address(i));
    				   					   
    end generate msb_stack_count;

  end generate stack_count_loop;

--
------------------------------------------------------------------------------------
--
-- End of description for KCPSM3 macro.
--
------------------------------------------------------------------------------------
--
--**********************************************************************************
-- Code for simulation purposes only after this line
--**********************************************************************************
--
------------------------------------------------------------------------------------
--
-- Code for simulation.
--
-- Disassemble the instruction codes to form a text string variable for display.
-- Determine status of reset and flags and present in the form of a text string.
-- Provide a local variables to simulate the contents of each register and scratch 
-- pad memory location.
--
------------------------------------------------------------------------------------
--
  --All of this section is ignored during synthesis.
  --synthesis translate off

  simulation: process (clk, instruction)
  --
  --complete instruction decode
  --
  variable kcpsm3_opcode : string(1 to 19);
  --
  --Status of flags and processor
  --
  variable kcpsm3_status : string(1 to 13):= "NZ, NC, Reset";

  --
  --contents of each register
  --
  variable s0_contents : std_logic_vector(7 downto 0):=X"00";
  variable s1_contents : std_logic_vector(7 downto 0):=X"00";
  variable s2_contents : std_logic_vector(7 downto 0):=X"00";
  variable s3_contents : std_logic_vector(7 downto 0):=X"00";
  variable s4_contents : std_logic_vector(7 downto 0):=X"00";
  variable s5_contents : std_logic_vector(7 downto 0):=X"00";
  variable s6_contents : std_logic_vector(7 downto 0):=X"00";
  variable s7_contents : std_logic_vector(7 downto 0):=X"00";
  variable s8_contents : std_logic_vector(7 downto 0):=X"00";
  variable s9_contents : std_logic_vector(7 downto 0):=X"00";
  variable sa_contents : std_logic_vector(7 downto 0):=X"00";
  variable sb_contents : std_logic_vector(7 downto 0):=X"00";
  variable sc_contents : std_logic_vector(7 downto 0):=X"00";
  variable sd_contents : std_logic_vector(7 downto 0):=X"00";
  variable se_contents : std_logic_vector(7 downto 0):=X"00";
  variable sf_contents : std_logic_vector(7 downto 0):=X"00";
  --
  --contents of each scratch pad memory location
  --
  variable spm00_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm01_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm02_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm03_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm04_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm05_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm06_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm07_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm08_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm09_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm0a_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm0b_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm0c_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm0d_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm0e_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm0f_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm10_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm11_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm12_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm13_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm14_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm15_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm16_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm17_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm18_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm19_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm1a_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm1b_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm1c_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm1d_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm1e_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm1f_contents : std_logic_vector(7 downto 0):=X"00";  
  variable spm20_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm21_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm22_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm23_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm24_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm25_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm26_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm27_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm28_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm29_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm2a_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm2b_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm2c_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm2d_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm2e_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm2f_contents : std_logic_vector(7 downto 0):=X"00";  
  variable spm30_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm31_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm32_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm33_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm34_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm35_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm36_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm37_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm38_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm39_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm3a_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm3b_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm3c_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm3d_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm3e_contents : std_logic_vector(7 downto 0):=X"00";
  variable spm3f_contents : std_logic_vector(7 downto 0):=X"00";
  --
  --temporary variables
  --
  variable     sx_decode : string(1 to 2);                     --sX register specification
  variable     sy_decode : string(1 to 2);                     --sY register specification
  variable     kk_decode : string(1 to 2);                     --constant value specification
  variable    aaa_decode : string(1 to 3);                     --address specification
  --
  --------------------------------------------------------------------------------
  --
  -- Function to convert 4-bit binary nibble to hexadecimal character
  --
  --------------------------------------------------------------------------------
  --
  function hexcharacter (nibble: std_logic_vector(3 downto 0))
  return character is
  variable hex: character;
  begin
    case nibble is
      when "0000" => hex := '0';
      when "0001" => hex := '1';
      when "0010" => hex := '2';
      when "0011" => hex := '3';
      when "0100" => hex := '4';
      when "0101" => hex := '5';
      when "0110" => hex := '6';
      when "0111" => hex := '7';
      when "1000" => hex := '8';
      when "1001" => hex := '9';
      when "1010" => hex := 'A';
      when "1011" => hex := 'B';
      when "1100" => hex := 'C';
      when "1101" => hex := 'D';
      when "1110" => hex := 'E';
      when "1111" => hex := 'F';
      when others => hex := 'x';
    end case;
    return hex;
  end hexcharacter;
  --
  --------------------------------------------------------------------------------
  --
  begin
     
    -- decode first register
    sx_decode(1) := 's';
    sx_decode(2) := hexcharacter(instruction(11 downto 8));             

    -- decode second register
    sy_decode(1) := 's';
    sy_decode(2) := hexcharacter(instruction(7 downto 4));  

    -- decode constant value
    kk_decode(1) := hexcharacter(instruction(7 downto 4));
    kk_decode(2) := hexcharacter(instruction(3 downto 0));

    -- address value
    aaa_decode(1) := hexcharacter("00" & instruction(9 downto 8));
    aaa_decode(2) := hexcharacter(instruction(7 downto 4));
    aaa_decode(3) := hexcharacter(instruction(3 downto 0));

    -- decode instruction
    case instruction(17 downto 12) is
      when "000000" => kcpsm3_opcode := "LOAD " & sx_decode & ',' & kk_decode & "         ";
      when "000001" => kcpsm3_opcode := "LOAD " & sx_decode & ',' & sy_decode & "         ";
      when "001010" => kcpsm3_opcode := "AND " & sx_decode & ',' & kk_decode & "          ";
      when "001011" => kcpsm3_opcode := "AND " & sx_decode & ',' & sy_decode & "          ";
      when "001100" => kcpsm3_opcode := "OR " & sx_decode & ',' & kk_decode & "           ";
      when "001101" => kcpsm3_opcode := "OR " & sx_decode & ',' & sy_decode & "           ";
      when "001110" => kcpsm3_opcode := "XOR " & sx_decode & ',' & kk_decode & "          ";
      when "001111" => kcpsm3_opcode := "XOR " & sx_decode & ',' & sy_decode & "          ";
      when "010010" => kcpsm3_opcode := "TEST " & sx_decode & ',' & kk_decode & "         ";
      when "010011" => kcpsm3_opcode := "TEST " & sx_decode & ',' & sy_decode & "         ";
      when "011000" => kcpsm3_opcode := "ADD " & sx_decode & ',' & kk_decode & "          ";
      when "011001" => kcpsm3_opcode := "ADD " & sx_decode & ',' & sy_decode & "          ";
      when "011010" => kcpsm3_opcode := "ADDCY " & sx_decode & ',' & kk_decode & "        ";
      when "011011" => kcpsm3_opcode := "ADDCY " & sx_decode & ',' & sy_decode & "        ";
      when "011100" => kcpsm3_opcode := "SUB " & sx_decode & ',' & kk_decode & "          ";
      when "011101" => kcpsm3_opcode := "SUB " & sx_decode & ',' & sy_decode & "          ";
      when "011110" => kcpsm3_opcode := "SUBCY " & sx_decode & ',' & kk_decode & "        ";
      when "011111" => kcpsm3_opcode := "SUBCY " & sx_decode & ',' & sy_decode & "        ";
      when "010100" => kcpsm3_opcode := "COMPARE " & sx_decode & ',' & kk_decode & "      ";
      when "010101" => kcpsm3_opcode := "COMPARE " & sx_decode & ',' & sy_decode & "      ";
      when "100000" => 
        case instruction(3 downto 0) is
          when "0110" => kcpsm3_opcode := "SL0 " & sx_decode & "             ";
          when "0111" => kcpsm3_opcode := "SL1 " & sx_decode & "             ";
          when "0100" => kcpsm3_opcode := "SLX " & sx_decode & "             ";
          when "0000" => kcpsm3_opcode := "SLA " & sx_decode & "             ";
          when "0010" => kcpsm3_opcode := "RL " & sx_decode & "              ";
          when "1110" => kcpsm3_opcode := "SR0 " & sx_decode & "             ";
          when "1111" => kcpsm3_opcode := "SR1 " & sx_decode & "             ";
          when "1010" => kcpsm3_opcode := "SRX " & sx_decode & "             ";
          when "1000" => kcpsm3_opcode := "SRA " & sx_decode & "             ";
          when "1100" => kcpsm3_opcode := "RR " & sx_decode & "              ";
          when others => kcpsm3_opcode := "Invalid Instruction";
        end case;
      when "101100" => kcpsm3_opcode := "OUTPUT " & sx_decode & ',' & kk_decode & "       ";
      when "101101" => kcpsm3_opcode := "OUTPUT " & sx_decode & ",(" & sy_decode & ")     ";
      when "000100" => kcpsm3_opcode := "INPUT " & sx_decode & ',' & kk_decode & "        ";
      when "000101" => kcpsm3_opcode := "INPUT " & sx_decode & ",(" & sy_decode & ")      ";
      when "101110" => kcpsm3_opcode := "STORE " & sx_decode & ',' & kk_decode & "        ";
      when "101111" => kcpsm3_opcode := "STORE " & sx_decode & ",(" & sy_decode & ")      ";
      when "000110" => kcpsm3_opcode := "FETCH " & sx_decode & ',' & kk_decode & "        ";
      when "000111" => kcpsm3_opcode := "FETCH " & sx_decode & ",(" & sy_decode & ")      ";
      when "110100" => kcpsm3_opcode := "JUMP " & aaa_decode & "           ";
      when "110101" =>
        case instruction(11 downto 10) is
          when "00" => kcpsm3_opcode := "JUMP Z," & aaa_decode & "         ";
          when "01" => kcpsm3_opcode := "JUMP NZ," & aaa_decode & "        ";
          when "10" => kcpsm3_opcode := "JUMP C," & aaa_decode & "         ";
          when "11" => kcpsm3_opcode := "JUMP NC," & aaa_decode & "        ";
          when others => kcpsm3_opcode := "Invalid Instruction";
        end case;
      when "110000" => kcpsm3_opcode := "CALL " & aaa_decode & "           ";
      when "110001" =>
        case instruction(11 downto 10) is
          when "00" => kcpsm3_opcode := "CALL Z," & aaa_decode & "         ";
          when "01" => kcpsm3_opcode := "CALL NZ," & aaa_decode & "        ";
          when "10" => kcpsm3_opcode := "CALL C," & aaa_decode & "         ";
          when "11" => kcpsm3_opcode := "CALL NC," & aaa_decode & "        ";
          when others => kcpsm3_opcode := "Invalid Instruction";
        end case;
      when "101010" => kcpsm3_opcode := "RETURN             ";
      when "101011" =>
        case instruction(11 downto 10) is
          when "00" => kcpsm3_opcode := "RETURN Z           ";
          when "01" => kcpsm3_opcode := "RETURN NZ          ";
          when "10" => kcpsm3_opcode := "RETURN C           ";
          when "11" => kcpsm3_opcode := "RETURN NC          ";
          when others => kcpsm3_opcode := "Invalid Instruction";
        end case;
      when "111000" =>
        case instruction(0) is
          when '0' => kcpsm3_opcode := "RETURNI DISABLE    ";
          when '1' => kcpsm3_opcode := "RETURNI ENABLE     ";
          when others => kcpsm3_opcode := "Invalid Instruction";
        end case;
      when "111100" =>
        case instruction(0) is
          when '0' => kcpsm3_opcode := "DISABLE INTERRUPT  ";
          when '1' => kcpsm3_opcode := "ENABLE INTERRUPT   ";
          when others => kcpsm3_opcode := "Invalid Instruction";
        end case;
      when others => kcpsm3_opcode := "Invalid Instruction";
    end case;

    if clk'event and clk='1' then 

      --reset and flag status information
      if reset='1' or reset_delay='1' then
        kcpsm3_status := "NZ, NC, Reset";
       else
        kcpsm3_status(7 to 13) := "       ";
        if flag_enable='1' then
          if zero_carry='1' then
            kcpsm3_status(1 to 4) := " Z, ";
           else
            kcpsm3_status(1 to 4) := "NZ, ";
          end if;
          if sel_carry(3)='1' then
            kcpsm3_status(5 to 6) := " C";
           else
            kcpsm3_status(5 to 6) := "NC";
          end if;
        end if;
      end if;

      --simulation of register contents
      if register_enable='1' then
        case instruction(11 downto 8) is
          when "0000" => s0_contents := alu_result;
          when "0001" => s1_contents := alu_result;
          when "0010" => s2_contents := alu_result;
          when "0011" => s3_contents := alu_result;
          when "0100" => s4_contents := alu_result;
          when "0101" => s5_contents := alu_result;
          when "0110" => s6_contents := alu_result;
          when "0111" => s7_contents := alu_result;
          when "1000" => s8_contents := alu_result;
          when "1001" => s9_contents := alu_result;
          when "1010" => sa_contents := alu_result;
          when "1011" => sb_contents := alu_result;
          when "1100" => sc_contents := alu_result;
          when "1101" => sd_contents := alu_result;
          when "1110" => se_contents := alu_result;
          when "1111" => sf_contents := alu_result;
          when others => null;
        end case;
      end if;

      --simulation of scratch pad memory contents
      if memory_enable='1' then
        case second_operand(5 downto 0) is
          when "000000" => spm00_contents := sx;
          when "000001" => spm01_contents := sx;
          when "000010" => spm02_contents := sx;
          when "000011" => spm03_contents := sx;
          when "000100" => spm04_contents := sx;
          when "000101" => spm05_contents := sx;
          when "000110" => spm06_contents := sx;
          when "000111" => spm07_contents := sx;
          when "001000" => spm08_contents := sx;
          when "001001" => spm09_contents := sx;
          when "001010" => spm0a_contents := sx;
          when "001011" => spm0b_contents := sx;
          when "001100" => spm0c_contents := sx;
          when "001101" => spm0d_contents := sx;
          when "001110" => spm0e_contents := sx;
          when "001111" => spm0f_contents := sx;
          when "010000" => spm10_contents := sx;
          when "010001" => spm11_contents := sx;
          when "010010" => spm12_contents := sx;
          when "010011" => spm13_contents := sx;
          when "010100" => spm14_contents := sx;
          when "010101" => spm15_contents := sx;
          when "010110" => spm16_contents := sx;
          when "010111" => spm17_contents := sx;
          when "011000" => spm18_contents := sx;
          when "011001" => spm19_contents := sx;
          when "011010" => spm1a_contents := sx;
          when "011011" => spm1b_contents := sx;
          when "011100" => spm1c_contents := sx;
          when "011101" => spm1d_contents := sx;
          when "011110" => spm1e_contents := sx;
          whe