What is the structural VHDL program for 8 to 1 multiplexer?

Answer 1

A structural VHDL program for an 8-to-1 multiplexer defines the multiplexer using lower-level components, such as 2-to-1 multiplexers. You can instantiate several 2-to-1 multiplexers to create the 8-to-1 functionality. The 8 input signals are combined through three levels of 2-to-1 multiplexers, where the first level reduces the inputs from 8 to 4, the second from 4 to 2, and the final level selects the output from 2 inputs. Below is a simple structural VHDL example:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity MUX8to1 is
    Port ( A : in  STD_LOGIC_VECTOR(7 downto 0);
           S : in  STD_LOGIC_VECTOR(2 downto 0);
           Y : out STD_LOGIC);
end MUX8to1;

architecture Structural of MUX8to1 is
    signal MUX1_out, MUX2_out, MUX3_out, MUX4_out : STD_LOGIC;

begin
    MUX1: entity work.MUX2to1 port map (A(0), A(1), S(0), MUX1_out);
    MUX2: entity work.MUX2to1 port map (A(2), A(3), S(0), MUX2_out);
    MUX3: entity work.MUX2to1 port map (A(4), A(5), S(0), MUX3_out);
    MUX4: entity work.MUX2to1 port map (A(6), A(7), S(0), MUX4_out);
    
    MUX5: entity work.MUX2to1 port map (MUX1_out, MUX2_out, S(1), Y_temp1);
    MUX6: entity work.MUX2to1 port map (MUX3_out, MUX4_out, S(1), Y_temp2);
    
    MUX7: entity work.MUX2to1 port map (Y_temp1, Y_temp2, S(2), Y);
end Structural;

In this example, MUX2to1 is a previously defined 2-to-1 multiplexer entity. Each level of multiplexing reduces the number of inputs until the final output is selected based on the 3-bit select signal S.