By
Jonas Julian Jensen
Updated on
signal Sig1 : unsigned(7 downto 0) := x"AA";
signal Sig2 : unsigned(7 downto 0) := x"BB";
signal Sig3 : unsigned(7 downto 0) := x"CC";
signal Sig4 : unsigned(7 downto 0) := x"DD";
signal Sel : unsigned(1 downto 0) := (others => '0');
signal Output1 : unsigned(7 downto 0);
signal Output2 : unsigned(7 downto 0);
begin
-- Stimuli for the selector signal
process is
begin
wait for 10 ns;
Sel <= Sel + 1;
wait for 10 ns;
Sel <= Sel + 1;
wait for 10 ns;
Sel <= Sel + 1;
wait for 10 ns;
Sel <= Sel + 1;
wait for 10 ns;
Sel <= "UU";
wait;
end process;
-- MUX using if-then-else
process(Sel, Sig1, Sig2, Sig3, Sig4) is
begin
if Sel = "00" then
Output1 <= Sig1;
elsif Sel = "01" then
Output1 <= Sig2;
elsif Sel = "10" then
Output1 <= Sig3;
elsif Sel = "11" then
Output1 <= Sig4;
else -- 'U', 'X', '-' etc.
Output1 <= (others => 'X');
end if;
end process;
-- Equivalent MUX using a case statement
process(Sel, Sig1, Sig2, Sig3, Sig4) is
begin
case Sel is
when "00" =>
Output2 <= Sig1;
when "01" =>
Output2 <= Sig2;
when "10" =>
Output2 <= Sig3;
when "11" =>
Output2 <= Sig4;
when others => -- 'U', 'X', '-', etc.
Output2 <= (others => 'X');
end case;
end process;
end architecture;
The waveform window in ModelSim after we pressed run and zoomed in on the timeline:
