cnt500.vhd

dds信号发生器

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity cnt500 is
port(clk:in std_logic;
				c500:out std_logic);
end;
architecture one of cnt500 is
signal q: std_logic_vector(8 downto 0);
begin
process(clk)
begin
			if clk'event and clk='1' then
					if (q<499) then q<=q+1;
					else q<="000000000";   
				    end if;
			end if;
end process;
process(q)
begin
	if q<250 then c500<='0';
	else c500<='1';
	end if;
end process;
end;