3 bit comparator

[Dương Dương]

comparator3bit.vhd:library IEEE;
use IEEE.STD_LOGIC_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity comparator3bit is
port (
p : in std_logic_vector(2 downto 0);
q : in std_logic_vector(2 downto 0);
p_le_q : out std_logic
);
end comparator3bit;

Architecture Behavior of comparator3bit is
begin
process (p, q)
begin
if p<q then p_le_q <= '1';
else p_le_q <= '0';
end if;
end process;
end Behavior;

comparator3bit_tb.vhd:
library IEEE;
use IEEE.STD_LOGIC_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
USE ieee.numeric_std.ALL;

entity comparator3bit_tb is
end comparator3bit_tb;

Architecture tb of comparator3bit_tb is
component comparator3bit_tb is
port ( p : in std_logic_vector(2 downto 0);
q : in std_logic_vector(2 downto 0);
p_le_q : out std_logic);
end component;
signal p,q : std_logic_vector(2 downto 0) := (others => '0');
signal p_le_q : std_logic;
signal i,j : integer;
begin
UUT : entity work.comparator3bit port map (p => p, q => q ,p_le_q => p_le_q);
process
begin
for i in 0 to 8 loop
p <= std_logic_vector(to_unsigned(i+2,3));
q <= std_logic_vector(to_unsigned(i,3));
end loop;
wait;
end process;
end;

When I run the simulation comparator3bit_tb and add the wave then the graph does not show p_le_q output. How to fix thanks

[Maurice SAAB]

you should wait for some time after assigning p and q, try this:

for i in 0 to 8 loop
for i in 0 to 8 loop
p <= std_logic_vector(to_unsigned(i+2,3));
q <= std_logic_vector(to_unsigned(i,3));
end loop;
wait;

HTH





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[Maurice SAAB]

wait for 100 ns;

[Charles Bailey]

Main problem: your FOR loop doesn't advance simulation time with each
iteration. Your whole simulation completes in 0 ps. Put a WAIT
statement, such as "wait for 20 ns;" before the "end loop;"

A few other comments:
Remove the references to the std_logic_arith and std_logic_unsigned
packages. Those are non-standard packages that came from Synopsys, not
IEEE, and are considered deprecated. Plus, you are not actually using
them anyway.

Because your testbench uses entity instantiation for comparator3bit, you
don't need the component definition for it.

Charles Bailey