xset.vhd

24秒倒计时系统（有跑马灯） 利用CPLD

library IEEE;
use IEEE.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use ieee.std_logic_arith.all;

entity xset is
	port(time:in std_logic_vector(5 downto 0);
		reset:in std_logic;
		clk:in std_logic;
		sel:out std_logic;
		d_out:out std_logic_vector(3 downto 0)
		);
end xset;

architecture arc_xset of xset is
signal sel1:std_logic;
begin
process(clk,reset,time)
begin
if reset='0' then
	sel<='0';
	d_out<="0000";
	sel1<='0';
else
	if (clk='1' and clk'event) then
		sel1<=not sel1;
	end if;
	sel<=sel1;
	case sel1 is
		when '0'=>d_out(3)<='0';
				d_out(2)<='0';
				d_out(1)<=time(5);
				d_out(0)<=time(4);
		when '1'=>d_out<=time(3 downto 0);
		when others=>null;
	end case;
end if;
end process;
end arc_xset;