Subversion Repositories v6502

library IEEE;

use IEEE.std_logic_1164.all;  -- defines std_logic types

use IEEE.STD_LOGIC_unsigned.all;

use IEEE.STD_LOGIC_arith.all;

-- 8 bit three-way multiplexer

entity dmux is

  port(  sel:  in STD_LOGIC_VECTOR(1 downto 0);

           a:  in STD_LOGIC_VECTOR(7 downto 0);

           b:  in STD_LOGIC_VECTOR(7 downto 0);

           c:  in STD_LOGIC_VECTOR(7 downto 0);

           y: out STD_LOGIC_VECTOR(7 downto 0)

      );

end dmux;

architecture comb of dmux is

constant NOP_D: STD_LOGIC_VECTOR(1 downto 0) := "00";

constant ORD_D: STD_LOGIC_VECTOR(1 downto 0) := "01";

constant EXT_D: STD_LOGIC_VECTOR(1 downto 0) := "10";

constant BCD_D: STD_LOGIC_VECTOR(1 downto 0) := "11";

begin

  process(sel,a,b,c)

  begin

    case sel is

      when ORD_D    => y <= a;

      when EXT_D    => y <= b;

      when BCD_D    => y <= c;

      when others   => y <= "00000000";

    end case;

  end process;

end comb;