counter.vhd

基于VHDL实现的十字路口交通灯功能

library ieee;
use ieee.std_logic_1164.all;

entity counter is
port 
(clk:in std_logic;
hold: in std_logic;
reset: in std_logic;
num: buffer integer range 0 to 49);
end;

architecture b_counter of counter is
begin
 process(clk,reset)
  begin
   if reset='1' then
     num<=0;
   elsif rising_edge(clk) then
     if hold='1' then
       num<=num;
       else 
     if num=49 then
      num<=0;
      else
     num<=num+1;
end if;
end if;
end if;
end process;
end b_counter;