11.2.3.6 Relational Operators

Relational operators compare two operands and indicate whether the comparison is true or false. The following examples infer greater than, less than, greater than equal to, and less than equal to comparators. Synthesis tools generally optimize relational operators for the target technology.

VHDL

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
entity relational is
port (A, B : in std_logic_vector(3 downto 0);
Q1, Q2, Q3, Q4 : out std_logic);
end relational;
architecture behav of relational is
begin
process (A, B)
begin
-- Q1 <= A > B; -- greater than
-- Q2 <= A < B; -- less than
-- Q3 <= A >= B; -- greater than equal to
if (A <= B) then –- less than equal to
Q4 <= '1';
else
Q4 <= '0';
end if;
end process;
end behav;

Verilog

module relational (A, B, Q1, Q2, Q3, Q4);
input [3:0] A, B;
output Q1, Q2, Q3, Q4;
reg Q1, Q2, Q3, Q4;
always @ (A or B)
begin
// Q1 = A > B; //greater than
// Q2 = A < B; //less than
// Q3 = A >= B; //greater than equal to
if (A <= B) //less than equal to
Q4 = 1;
else
Q4 = 0;
end
endmodule