hou.vhd

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--------24进制计数器模块  计数输出为小时的数值
library ieee; 
use ieee.std_logic_1164.all; 
use ieee.std_logic_unsigned.all; 
------------------------------------
entity hou is 
port(en,clk,clr:in std_logic; 
h1,h0:out std_logic_vector(3 downto 0)); 
end hou; 
-----------------------------------------
architecture hour_arc of hou is 
begin 
process(clk) 
variable cnt0,cnt1:std_logic_vector(3 downto 0); 
begin 
if clr='0'then      ----清零
cnt0:="0000"; 
cnt1:="0000"; 
elsif clk'event and clk='1'then    ---在时钟的上升沿，
if en='1'then           ----使能端有