Subversion Repositories mcu8

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

USE work.cpu_types.ALL;

entity reg is

  port( clk, rst : IN std_logic;        -- high-active asynch rst

--        a_in : in d_bus; -- register a

--        b_in : in d_bus; -- register b

        result_in : d_bus;

        rom_data_in : d_bus;

        carry_in : IN std_logic;

        zero_in : in std_logic;

        a_out : out d_bus; -- register a

        b_out : out d_bus; -- register b

        carry_out : out std_logic;

        zero_out : out STD_LOGIC;

        control : IN opcode );          -- extend the control from the CU

end reg;

architecture behavioral of reg is

  signal rom_data_intern : d_bus;

begin

reg_rom: process(clk)

begin

  if clk'event and clk='1' then

    if rst='1' then

      rom_data_intern <= (others => '0');

    else

      rom_data_intern <= rom_data_in;

    end if;

  end if;

end process;

reg_p: process(clk)

  BEGIN

    IF clk'EVENT AND clk='1' THEN

      if rst='1' THEN

        a_out <= (OTHERS => '0');

        b_out <= (OTHERS => '0');

        zero_out <= '0';

        carry_out <= '0';

      else

        CASE control IS

          WHEN neg_s | and_s | exor_s | or_s | sra_s | ror_s | add_s | addc_s =>

            zero_out <= zero_in;

            a_out <= result_in;

            carry_out <= carry_in;

          WHEN lda_const_2 => zero_out <= zero_in;

                              a_out <= rom_data_intern;

                              carry_out <= carry_in;

          when lda_const_1 => zero_out <= zero_in;

          WHEN ldb_const_2 => zero_out <= zero_in;

                              b_out <= rom_data_intern;

                              carry_out <= carry_in;

          WHEN lda_addr_2 =>  zero_out <= zero_in;

                              a_out <= result_in;

                              carry_out <= carry_in;

          WHEN ldb_addr_2 =>  zero_out <= zero_in;

                              b_out <= result_in;

                              carry_out <= carry_in;

          WHEN OTHERS => NULL;

        END CASE;

      END if;

    end if;

end process;

end behavioral;