Search code examples
vhdlhardwarehdlxilinx-isehardware-design

Multiplexer in vhdl with structural design

I am totally new to VHDL and I want to implement the following MUX for a logical implication S0 => S1 without using other gates.

4-1 MUX

I want to use structural design, but one of my main problems is that I don't understand how to map the ports correctly so that I am implementing the given implication.

My code so far is compiling and iSim starts but I get two warnings:

  1. mux41_impl remains a black-box sinse it has no binding entity.
  2. mux_out_test has value U

Furthermore, I understand that my component has to match the entity exactly but if I rename it to the entities name I am getting an illegal recurion message.

code

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity MUX41_IMPL_top is
port (
    D0, D1, D2, D3, S0, S1: in STD_LOGIC;
    mux_out : out STD_LOGIC
);
end MUX41_IMPL_top;

architecture structure of MUX41_IMPL_top is

component MUX41_IMPL
    port (
        D0, D1, D2, D3, S0, S1: in STD_LOGIC;
        mux_out : out STD_LOGIC
    );
end component;

begin

u1: MUX41_IMPL port map (D0, D1, D2, D3, S0, S1, mux_out);
end structure;

testbench code

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity MUX41_IMPL_SIMBOX is
end MUX41_IMPL_SIMBOX;

architecture TEST_MUX41_IMPL of MUX41_IMPL_SIMBOX is

component MUX41_IMPL is
    port (
        D0, D1, D2, D3, S0, S1: in STD_LOGIC;
        mux_out : out STD_LOGIC
    );
end component;

signal D0_test : STD_LOGIC := '1';
signal D1_test : STD_LOGIC := '0';
signal D2_test : STD_LOGIC := '1';
signal D3_test : STD_LOGIC := '1';
signal S0_test, S1_test : STD_LOGIC := '0';
signal mux_out_test : STD_LOGIC;

for my_MUX41_IMPL : MUX41_IMPL use entity work.MUX41_IMPL_top(structure);

begin
    my_MUX41_IMPL : MUX41_IMPL
    port map (
    D0 => D0_test,
    D1 => D1_test,
    D2 => D2_test,
    D3 => D3_test,
    S0 => S0_test,
    S1 => S1_test,
    mux_out => mux_out_test
    );

    S0_test <= not S0_test after 2 ns;
    S1_test <= not S1_test after 4 ns;

end TEST_MUX41_IMPL;
Solution 
  • entity MUX41_IMPL_top is
port (
    D0, D1, D2, D3: in STD_LOGIC;
    Sel : in std_logic_vector(1 downto 0);    
    mux_out : out STD_LOGIC

);
end MUX41_IMPL_top;

architecture structure of MUX41_IMPL_top is
begin

with Sel select
    mux_out <=  D0 when "00",
                D1 when "01",
                D2 when "10",            
                D3 when "11",            
                '0' when others;    

architecture structure;