1.--VHDL中，wait until clk='1' 可代clk'event and clk='1'做上升沿，
--wait until clk='0' 可代clk'event and clk='1'做下降沿。用法如下：
--74hc161功能芯片的VHDL程序：
Library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity d_ff is
Port(clk,cr,ld:in std_logic;
d:in std_logic_vector(3 downto 0);
q:out std_logic_vector(3 downto 0));
end;
architecture dd of d_ff is
signal s,ss:std_logic_vector(3 downto 0);
begin
process
begin
wait until clk='1'; --这句意思是等待到clk等于1时完成下面语句
if ld='0' then s<=d;
else s<=s+1 ;
end if;
if cr='0' then
s<="0000";
end if;
end process;
q<=s;
end dd;
2--子程序也是很多编程语言中常用的程序模块，VHDL子程序用法如下：
1）---------------子程序function的用法--------
Library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity full_adder is
Port(a,b,cin:in std_logic;
sum,co:out std_logic);
end;
architecture add of full_adder is Function sam1(x,y:std_logic)return std_logic is --子程序1，sam1为程序名
begin --x,y为子程序变量，冒号后面是变量类型
return (x xor y); --子程序返回值
end sam1; --结束子程序1
function sam2(x,y:std_logic)return std_logic is --子程序2
begin
return (x and y);
end sam2; --结束子程序1
signal s1,co1,s2,co2,ss:std_logic;
begin
process(a,b,cin)
begin
s1<=sam1(a,b); --调用子程序1
co1<=sam2(a,b); --调用子程序2
s2<=sam1(s1,cin);
co2<=sam2(s1,cin);
end process;
sum<=s2;
co<=co1 or co2;
end dd;
2）---------------子程序Procedure的用法---------
Library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity d_ff is
Port(a,b,cin:in std_logic;
sum,co:out std_logic);
end;
architecture dd of d_ff is
---------------------------------------
Procedure sam(x,y:in std_logic;
z,w: out std_logic) is --这个子程序用法变量必须设置方向
begin
z:=x xor y; --赋值必须采用变量Veriable格式:=
w:=x and y;
end sam;
begin
process(a,b,cin)
variable s1,s2,co1,co2:std_logic;--运行过程中需要的话，必须使用局部变量，在Process后设置。
begin
sam(a,b,s1,co1);
sam(cin,s1,s2,co2);
sum<=s2;
co<=co1 or co2;
end process;
end dd;
3.程序块Block的编辑与使用
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
ENTITY ppp IS
PORT(a,b,c,D,clk: IN STD_LOGIC;
y,s,co,Q: OUT STD_LOGIC);
END ppp;
ARCHITECTURE Behave OF ppp IS
signal tmp1,tmp2,tmp3,tmp4,s1,c1,s2,c2:STD_LOGIC;
BEGIN
g1:BLOCK
BEGIN
process(clk)
begin
tmp1 <= a and b;
tmp2<= a and (b or (not c));
tmp3<=c xor(not( a and b));
if clk'event and clk='1' then
y<=tmp3 or (tmp2 and tmp1);
end if;
end process;
END BLOCK g1;
g2:block
begin
s1<= a xor b;
c1<= a and b;
s<=s1 xor c;
c2<=s1 and c;
co<=c1 or c2;
end block g2;
G3:block
begin
process(D,clk)
begin
if clk'event and clk='1' then
Q<=D;
end if;
end process;
end block g3;
END Behave;
4. for i in 0 to 7 loop 语句
------------------------------------------------------
library ieee;
use ieee.std_logic_1164.all;
entity fulladder is
Port(D:in std_logic_vector(7 downto 0);
clk:in std_logic;
Q:out std_logic_vector(7 downto 0));
end;
architecture add of fulladder is
begin
process(D,clk)
begin
for i in 0 to 7 loop
if clk'event and clk='1' then
q(i)<=d(i);
end if;
end loop;
end process;
end;
-------------------------------------------------------------------
5.quartusII11.0程序综合通过后要生成图像按下图操作
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