kcount.vhd

里面有一个很实用的源码,数字引爆密码设计

LIBRARY IEEE;
USE IEEE.std_logic_1164.ALL;
USE IEEE.std_logic_arith.ALL;
USE IEEE.std_logic_unsigned.ALL;

ENTITY kcount IS
           PORT (A,B    : IN  std_logic;
                 C,D,E  : OUT  std_logic);
END kcount;

ARCHITECTURE kcount_arc OF kcount IS
BEGIN
     PROCESS(A,B)
     VARIABLE  counter  : integer RANGE 0 TO 3;
     CONSTANT  md  : integer := 3;
     BEGIN
          IF (B = '1') THEN
             counter := 0;
             E <= '0';
          ELSIF (A'event AND A = '1') THEN
             counter := counter +1;
             IF (counter = md) THEN
                 counter := 0;
                 E <= '1';
             END IF;
          END IF; 

          IF (counter = 0) THEN
             C <= '0';  D <= '0';
          ELSIF (counter = 1) THEN
             C <= '1';  D <= '0';
          ELSE
             C <= '0';  D <= '1';
          END IF;
     END PROCESS;
END kcount_arc;