count24.vhd

一个用vhdl写的时钟代码

---------24进制计数作为一个整体
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use ieee.std_logic_arith.all;
entity count24 is
	port(clk4 : in std_logic;
		clr4 : in std_logic;
		value_lb: out std_logic_vector(3 downto 0);
		value_hb: out std_logic_vector(3 downto 0)
		);
end entity count24;
------------------------------------------
architecture behave of count24 is
 signal temp : std_logic_vector(4 downto 0);
  begin
P1: process(clk4,clr4)
	begin
	if clr4='1' then temp <=(others =>'0');
	elsif clk4'event and clk4='1' then
		if temp <23 then temp <= temp + 1;
		else temp <=(others =>'0');
		end if;
	else null;
	end if;
 end process;
P2: process(clk4,temp,clr4)
	 begin
	case temp is
	when "00000" => value_lb <= (others =>'0');-------------00
					value_hb <= (others =>'0');
	when "00001" => value_lb <= "0001";---------------------01
				    value_hb <="0000";
	when "00010" => value_lb <= "0010";---------------------02
					value_hb <="0000" ;
	when "00011" => value_lb <= "0011";---------------------03
					value_hb <="0000" ;
	when "00100" => value_lb <= "0100";---------------------04
					value_hb <="0000";
	when "00101" => value_lb <= "0101";---------------------05
					value_hb <="0000" ;
	when "00110" => value_lb <= "0110";---------------------06
					value_hb <= "0000";
	when "00111" => value_lb <= "0111";---------------------07
					value_hb <= "0000";
	when "01000" => value_lb <= "1000";---------------------08
					value_hb <="0000" ;
	when "01001" => value_lb <= "1001";---------------------09
					value_hb <= "0000";
	when "01010" => value_lb <= "0000";---------------------10
					value_hb <= "0001";
	when "01011" => value_lb <= "0001";---------------------11
					value_hb <= "0001";
	when "01100" => value_lb <= "0010";---------------------12
					value_hb <= "0001";
	when "01101" => value_lb <= "0011";---------------------13
					value_hb <= "0001";
	when "01110" => value_lb <= "0100";---------------------14
					value_hb <= "0001";
	when "01111" => value_lb <= "0101";----------------------15
					value_hb <= "0001";
	when "10000" => value_lb <= "0110";----------------------16
					value_hb <= "0001";
	when "10001" => value_lb <= "0111";----------------------17
					value_hb <= "0001";
	when "10010" => value_lb <= "1000";----------------------18
					value_hb <= "0001";
	when "10011" => value_lb <= "1001";----------------------19
					value_hb <= "0001";
	when "10100" => value_lb <= "0000";----------------------20
					value_hb <= "0010";
	when "10101" => value_lb <= "0001";----------------------21
					value_hb <= "0010";
	when "10110" => value_lb <= "0010";----------------------22
					value_hb <= "0010";
	when "10111" => value_lb <= "0011";----------------------23
					value_hb <= "0010";
	when others => null;
   end case;
end process;
end architecture behave;