基于VHDL的层次化设计：异步清零和同步使能4位十六进制加法计数器和七段显示译码器的元件例化实现

原文：http://blog.csdn.net/Dr_JIA/article/details/45790579
方案一 （本实现方案只编写了一个vhdl文件，计数器和译码器的vhdl描述写在了一个文件里。本文件包含三个实体：分别是计数器counter4，译码器decoder，以及一个顶层实体HIERARCHIC，顶层文件里实现了计数器和译码器的结合。）
源程序:LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;

ENTITY HIERARCHIC IS
PORT(CP,R,EN:IN STD_LOGIC;
CO:OUT STD_LOGIC;
LED:OUT STD_LOGIC_VECTOR(6 DOWNTO 0));
END HIERARCHIC;

ARCHITECTURE HI OF HIERARCHIC IS
SIGNAL SIGN1:STD_LOGIC_VECTOR(3 DOWNTO 0);
COMPONENT COUNTER4
PORT(CP,R,EN:IN STD_LOGIC;
CO:OUT STD_LOGIC;
Q:BUFFER STD_LOGIC_VECTOR(3 DOWNTO0));
END COMPONENT;
COMPONENT DECODER
PORT(Ain:IN STD_LOGIC_VECTOR(3 DOWNTO 0);
LED:OUT STD_LOGIC_VECTOR(6 DOWNTO 0));
END COMPONENT;
BEGIN
U1:COUNTER4 PORT MAP(CP,R,EN,CO,SIGN1);
U2:DECODER PORT MAP(SIGN1,LED);
END HI;
---------------------------------------
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY COUNTER4 IS
PORT(CP,R,EN:IN STD_LOGIC;
Q:BUFFER STD_LOGIC_VECTOR(3 DOWNTO 0);
CO:OUT STD_LOGIC);
END COUNTER4;
ARCHITECTURE COUNT OF COUNTER4 IS
BEGIN
PROCESS(CP,R)
BEGIN
IF(R='1')THEN Q<="0000";
ELSIF(CP'EVENT AND CP='1'AND EN='1')THEN
IF(Q="1111")THEN Q<="0000";
ELSE Q<=Q+1;
END IF;
END IF;
END PROCESS;
CO<='1'WHEN Q=15 AND EN='1'ELSE'0';
END COUNT;
----------------------------------------
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;

ENTITY DECODER IS
PORT(Ain:IN STD_LOGIC_VECTOR(3 DOWNTO 0);
LED:OUT STD_LOGIC_VECTOR(6 DOWNTO 0));
END DECODER;

ARCHITECTURE DECODE OF DECODER IS
SIGNAL SIGN2:STD_LOGIC_VECTOR(6 DOWNTO 0);
BEGIN
WITH Ain SELECT
SIGN2<="0111111"WHEN"0000",
"0000110"WHEN"0001",
"1011011"WHEN"0010",
"1001111"WHEN"0011",
"1100110"WHEN"0100",
"1101101"WHEN"0101",
"1111101"WHEN"0110",
"0000111"WHEN"0111",
"1111111"WHEN"1000",
"1101111"WHEN"1001",
"1110111"WHEN"1010",
"1111100"WHEN"1011",
"0111001"WHEN"1100",
"1011110"WHEN"1101",
"1111001"WHEN"1110",
"1110001"WHEN"1111",
NULL WHEN OTHERS;
LED(6)<=SIGN2(6);
LED(5)<=SIGN2(5);
LED(4)<=SIGN2(4);
LED(3)<=SIGN2(3);
LED(2)<=SIGN2(2);
LED(1)<=SIGN2(1);
LED(0)<=SIGN2(0);
END DECODE;方案二（该实现方案编写了三个vhdl文件，即将方案一中的三个实体分开来写。在quartusII开发环境下，只要使新建工程名与实体名一致，然后将程序2、3包含到工程中即可。同样，在顶层实体中实现计数器和译码器的结合。方案一和方案二的顶层实体文件是完全相同的。）

hierarchi.vhd(顶层文件):
LIBRARY IEEE;

USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY HIERARCHIC IS
PORT(CP,R,EN:IN STD_LOGIC;
CO:OUT STD_LOGIC;
LED:OUT STD_LOGIC_VECTOR(6 DOWNTO 0));
END HIERARCHIC;
ARCHITECTURE HI OF HIERARCHIC IS
SIGNAL SIGN1:STD_LOGIC_VECTOR(3 DOWNTO 0);
COMPONENT COUNTER4
PORT(CP,R,EN:IN STD_LOGIC;
CO:OUT STD_LOGIC;
Q:BUFFER STD_LOGIC_VECTOR(3 DOWNTO0));
END COMPONENT;
COMPONENT DECODER
PORT(Ain:IN STD_LOGIC_VECTOR(3 DOWNTO 0);
LED:OUT STD_LOGIC_VECTOR(6 DOWNTO 0));
END COMPONENT;
BEGIN
U1:COUNTER4 PORT MAP(CP,R,EN,CO,SIGN1);
U2:DECODER PORT MAP(SIGN1,LED);
END HI;
4位十六进制计数器counter4.vhd:
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;

ENTITY COUNTER4 IS
PORT(CP,R,EN:IN STD_LOGIC;
Q:BUFFER STD_LOGIC_VECTOR(3 DOWNTO 0);
CO:OUT STD_LOGIC);
END COUNTER4;

ARCHITECTURE COUNT OF COUNTER4 IS
BEGIN
PROCESS(CP,R)
BEGIN
IF(R='1')THEN Q<="0000";
ELSIF(CP'EVENT AND CP='1'AND EN='1')THEN
IF(Q="1111")THEN Q<="0000";
ELSE Q<=Q+1;
END IF;
END IF;
END PROCESS;
CO<='1'WHEN Q=15 AND EN='1'ELSE'0';
END COUNT;七段显示译码器decoder.vhd:LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;

ENTITY DECODER IS
PORT(Ain:IN STD_LOGIC_VECTOR(3 DOWNTO 0);
LED:OUT STD_LOGIC_VECTOR(6 DOWNTO 0));
END DECODER;

ARCHITECTURE DECODE OF DECODER IS
SIGNAL SIGN2:STD_LOGIC_VECTOR(6 DOWNTO 0);
BEGIN
WITH Ain SELECT
SIGN2<="0111111"WHEN"0000",
"0000110"WHEN"0001",
"1011011"WHEN"0010",
"1001111"WHEN"0011",
"1100110"WHEN"0100",
"1101101"WHEN"0101",
"1111101"WHEN"0110",
"0000111"WHEN"0111",
"1111111"WHEN"1000",
"1101111"WHEN"1001",
"1110111"WHEN"1010",
"1111100"WHEN"1011",
"0111001"WHEN"1100",
"1011110"WHEN"1101",
"1111001"WHEN"1110",
"1110001"WHEN"1111",
NULL WHEN OTHERS;
LED(6)<=SIGN2(6);
LED(5)<=SIGN2(5);
LED(4)<=SIGN2(4);
LED(3)<=SIGN2(3);
LED(2)<=SIGN2(2);
LED(1)<=SIGN2(1);
LED(0)<=SIGN2(0);
END DECODE;后话：译码器的实现方案是多种多样的，大家在学习hdl语言时应充分注意活学活用。
以下再附三则decoder的实现方案，供各位参考。
实现方法之一：
（说明：本例直接在select语句中将结果赋给端口输出，而不再像源程序借助signal的那样。）
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;

ENTITY DECODER IS
PORT(Ain:IN STD_LOGIC_VECTOR(3 DOWNTO 0);
LED:OUT STD_LOGIC_VECTOR(6 DOWNTO 0));
END DECODER;

ARCHITECTURE DECODE OF DECODER IS
BEGIN
WITH Ain SELECT
LED<="0111111"WHEN"0000",
"0000110"WHEN"0001",
"1011011"WHEN"0010",
"1001111"WHEN"0011",
"1100110"WHEN"0100",
"1101101"WHEN"0101",
"1111101"WHEN"0110",
"0000111"WHEN"0111",
"1111111"WHEN"1000",
"1101111"WHEN"1001",
"1110111"WHEN"1010",
"1111100"WHEN"1011",
"0111001"WHEN"1100",
"1011110"WHEN"1101",
"1111001"WHEN"1110",
"1110001"WHEN"1111",
NULL WHEN OTHERS;
END DECODE;实现方法二：
（说明：本例的妙处是在process中使用for-loop语句，从而使信号的赋值变得简洁。当赋值语句更多时，
使用循环来实现重复的工作的优势将更加显著。注意：for-loop只能在process中出现。）LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;

ENTITY DECODER IS
PORT(Ain:IN STD_LOGIC_VECTOR(3 DOWNTO 0);
LED:OUT STD_LOGIC_VECTOR(6 DOWNTO 0));
END DECODER;

ARCHITECTURE DECODE OF DECODER IS
SIGNAL SIGN2:STD_LOGIC_VECTOR(6 DOWNTO 0);
BEGIN
WITH Ain SELECT
SIGN2<="0111111"WHEN"0000",
"0000110"WHEN"0001",
"1011011"WHEN"0010",
"1001111"WHEN"0011",
"1100110"WHEN"0100",
"1101101"WHEN"0101",
"1111101"WHEN"0110",
"0000111"WHEN"0111",
"1111111"WHEN"1000",
"1101111"WHEN"1001",
"1110111"WHEN"1010",
"1111100"WHEN"1011",
"0111001"WHEN"1100",
"1011110"WHEN"1101",
"1111001"WHEN"1110",
"1110001"WHEN"1111",
NULL WHEN OTHERS;
PROCESS(SIGN2)
BEGIN
FOR N IN 6 DOWNTO 0 LOOP
LED(N)<=SIGN2(N);
END LOOP;
END PROCESS;
END DECODE;实现方法三：
（说明：本例基于case语句。）LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;

ENTITY DECODER IS
PORT(Ain:IN STD_LOGIC_VECTOR(3 DOWNTO 0);
LED:OUT STD_LOGIC_VECTOR(6 DOWNTO 0));
END DECODER;

ARCHITECTURE DECODE OF DECODER IS
BEGIN
PROCESS(Ain)
BEGIN
CASE Ain IS
WHEN"0000"=>LED<="0111111";
WHEN"0001"=>LED<="0000110";
WHEN"0010"=>LED<="1011011";
WHEN"0011"=>LED<="1001111";
WHEN"0100"=>LED<="1100110";
WHEN"0101"=>LED<="1101101";
WHEN"0110"=>LED<="1111101";
WHEN"0111"=>LED<="0000111";
WHEN"1000"=>LED<="1111111";
WHEN"1001"=>LED<="1101111";
WHEN"1010"=>LED<="1110111";
WHEN"1011"=>LED<="1111100";
WHEN"1100"=>LED<="0111001";
WHEN"1101"=>LED<="1011110";
WHEN"1110"=>LED<="1111001";
WHEN"1111"=>LED<="1110001";
WHEN OTHERS=>LED<=NULL;
END CASE;
END PROCESS;
END DECODE;