zhongbai.vhd

基于FPGA的多功能电子时钟的设计很经典的哦

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity zhongbai is
port(clk:in std_logic;
	rst:in std_logic;
	q:out std_logic_vector(7 downto 0));
end;
architecture one of zhongbai is
	type states is(s0,s1);
	signal present :states;
	signal q1:std_logic_vector(7 downto 0);
	signal cnt:std_logic_vector(2 downto 0);
begin
process(clk,rst)
begin
if rst='1'then
	present<=s0;
	q1<=(others=>'0');
elsif clk'event and clk='1'then
	case present is
	when s0=>if q1="00000000"then
		q1<="10000000";
		else
			if cnt="111"then
				cnt<=(others=>'0');
				q1<="00000001";
				present<=s1;
			else q1<=q1(0)&q1(7 downto 1);
				cnt<=cnt+1;
				present<=s0;
			end if;
		end if;
	when s1=>if cnt="111"then
			cnt<=(others=>'0');
			q1<="10000000";
			present<=s0;
		else q1<=q1(6 downto 0)&q1(7);
			cnt<=cnt+1;
			present<=s1;
		end if;
	end case;
end if;
end process;
q<=q1;
end;