frequency_counter.vhdl

相位差测试

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity counter is
port (rst,clk : in std_logic;
      carry_in  : in std_logic;
      carry_out : out std_logic;
      count_out     : out std_logic_vector(3 downto 0));
end counter;
architecture Behavioral of counter is
	   signal count: std_logic_vector(3 downto 0):="0000";
begin
	process(rst,clk)
    	begin
		if rst='1' then
	    	count <= "0000";
		elsif clk'event and clk= '1' then
			if carry_in = '1' then
				if  count < "1001" then
		    		count <= count+1;
				else
		    		count <= "0000";
				end if;
	    		else
			null;
			end if;
		end if;	
  	end process;
      count_out<=count;
	  carry_out <= '1' when carry_in = '1' and count = "1001" else '0';
end Behavioral;