VHDL 例程

以下程序未经仿真，仅供说明

语法

声明参考库ieee,使用ieee中的std_logic_1164包全部条目可见

library ieee;  
use ieee.std_logic_1164.all;

程序框架

要点是：

1. 实体名和构造体名允许重复，都以“end 名字; ”结尾
2. port 括号里最后一行没有分号。目前发现只有实体里的port括号、元件申明语句里面的port括号里面各条目间以“;”分隔，其他情况的括号里面各条目间以“,”分隔。
3. 只有端口要标明信号方向如“in、out”，如实体里、元件声明里的port

library ieee;  
use ieee.std_logic_1164.all;

entity mux is 
	port(d0,d1,sel:in std_logic;
	q:out std_logic);
end mux; 

architecture rtl of mux is	 
begin						  
	process(d0,d1,sel)
	begin
		if(sel='0')then 
			q<=d0;
		elsif(sel='1')then
			q<=d1;
		else
			q<='Z';
		end if;
	end process;
	
end rtl;

元件申明和调用

要点：

1. 元件属性放在实体里
2. 元件申明component开头，不用is，以end component结尾。目前发现只有Type state_type is (S0,S1,S2);、实体和构造体和case中才有is，只有实体和构造体以end 自己定的名字;结尾
3. 注意参数映射、端口映射间没有逗号、分号

--被调用的元件
library ieee;
use ieee.std_logic_1164.all;

entity and2_gate is 
	generic(delay:time);
	port (
		in1,in2:in std_logic;
		out1:out std_logic); 
	
end and2_gate;				  

architecture beh of and2_gate is 
begin
	out1<=in1 and in2 after delay;
end beh;

--当前设计
library ieee;
use ieee.std_logic_1164.all;

entity nand2 is	
	port(a,b:in std_logic;
		q:out std_logic);
end nand2;				  

architecture structure of nand2 is 
	component and2_gate	  
		generic(delay:time);
		port (
			in1,in2:in std_logic;
			out1:out std_logic); 
	end component;	
	
	signal pass_state:std_logic;
begin		  
	q<=not pass_state;
	u1: and2_gate 
	generic map(5 ns)
	port map( a,b,pass_state);
end structure;

并行语句

所谓并行是：本语句和其他语句并发执行没有先后
并行赋值语句：条件信号赋值、选择信号赋值。process中只能有简单赋值和顺序描述语句
只有条件信号赋值和if语句才有else

	-----------条件信号赋值，有优先级
	t<=a when sel='0' else
	     b when sel='1' else
             'X';	
	-----------选择信号赋值，有优先级
	with sel select
		v<=a when '0',
		      b when '1',	  
		      'X' when others; 

顺序语句

顺序语句可以放在process里面，并行语句放在process外面
if是顺序语句，可以用来实现有优先级的分支
case 是顺序描述语句，各个分支没有优先级，各分支条件需穷举且不重复。

		case sel is 
			when "00"=>q<=a;
			when "01"=>q<=b;
			when "10"=>q<=c;
			when others=>q<=d;
		end case;

组合电路

基本逻辑门

门名称	符号
与门	and
或门	or
非门	not
与非	nand
或非	nor
异或	xor

编程方法一

library ieee;
use ieee.std_logic_1164.all;
entity and2 is
	port(
	a,b:in std_logic;
	y :out std_logic
	);
end and2; 
architecture rtl of and2 is 
begin
	y<=a and b;
end rtl;

编程方法二

library ieee;
use ieee.std_logic_1164.all;

entity and2 is 
	port(a,b:in std_logic;
	y:out std_logic);
end and2;			

architecture rtl of and2 is 
begin 
	process(a,b)
		variable comb:std_logic_vector(1 downto 0);
	begin
		comb:=a&b;
		case comb is 
			when "00"|"01"|"10"=>y<='0';
			when "11"=>y<='1';
			when others=>y<='X';
		end case;
	end process;
end rtl;

38译码器

library	 ieee;
use ieee.std_logic_1164.all;
entity decoder38 is
	port(a,b,c,g1,g2a,g2b:in std_logic;
	y:out std_logic_vector(7 downto 0));
end decoder38;

architecture rtl of decoder38 is 
signal indata:std_logic_vector(2 downto 0);
begin 									  
	indata<=a&b&c;
	process(indata,g1,g2a,g2b)
	begin		
		if(g1='1' and g2a='0' and g2b='0')then
			case indata is 
				when "000"=>y<=B"1111_1110";
				when "001"=>y<=B"1111_1101";
				when "010"=>y<=B"1111_1011";
				when "011"=>y<=B"1111_0111";		
				when "100"=>y<=B"1110_1111";
				when "101"=>y<=B"1101_1111";
				when "110"=>y<=B"1011_1111";
				when "111"=>y<=B"0111_1111";	
				when others=>y<=B"1111_1111";
			end case;
		else
			y<="11111111";
		end if;
	end process;
end rtl;

83优先级编码器

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity priorityencoder is
	port(input:in std_logic_vector(7 downto 0);
	y:out std_logic_vector(2 downto 0));
end priorityencoder;					 

architecture rtl of priorityencoder is
begin	
	process(input)
	begin		
		if(input(0)='0')then
			y<="111";
		elsif(input(1)='0')then
			y<="110";
		elsif(input(2)='0')then
			y<="101";
		elsif(input(3)='0')then
			y<="100";
		elsif(input(4)='0')then
			y<="011";
		elsif(input(5)='0')then
			y<="010";
		elsif(input(6)='0')then
			y<="001";
		else
			y<="000";  
		end if;	
	end process;
end rtl;

选择器

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity mux4 is	
	port(input:in std_logic_vector(3 downto 0);
	a,b:in std_logic;
	y:out std_logic);
end mux4;

architecture rtl of mux4 is
signal sel:std_logic_vector(1 downto 0);
begin				  					 
	sel<=a&b;
	process(sel,input) 
	begin		
		if(sel="00")then
			y<=input(0)	;
		elsif(sel="01")then
			y<=input(1)	;
		elsif(sel="10")then
			y<=input(2)	;
		elsif(sel="11")then
			y<=input(3);
		else 
			y<='Z';	
		end if;		
	end process;

end rtl;

比较器

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity comp4 is		
	port(a,b:in std_logic;
	GT:out std_logic;
	EQ:out std_logic;
	LT:out std_logic);
end comp4;

architecture rtl of comp4 is 
begin  
	process(a,b)
	begin
		if(a>b)then
			GT<='1';EQ<='0';LT<='0';
		elsif(a=b)then
			GT<='0';EQ<='1';LT<='0';
		else
			GT<='0';EQ<='0';LT<='1';
		end if;
	end process;
end rtl;

减法器

library ieee;
use ieee.std_logic_1164.all;
entity subtracter is
	port(x,y,cin:in std_logic;
	sub,cout:out std_logic);
end subtracter;
architecture rtl of subtracter is
begin	 
	sub<=x xor y xor cin;
	cout<=(not x and y)or (not x and cin)or (y and not cin);	
end rtl;

时序电路

异步D触发器

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity dffAsync is
	port(clk,d,clr_n:in std_logic;
	q:out std_logic);
end dffAsync;

architecture rtl of dffAsync is
begin
	process(clk,clr_n)
	begin		
		if(clr_n='0')then
			q<='0';
		elsif (clk'EVENT and clk='1')then
			q<=d;
		end if;
	end process;
	
end rtl;

同步D触发器

library ieee;
use ieee.std_logic_1164.all;
entity dffSync is 
	port(d,clk,clr_n:in std_logic;
	q:out std_logic);
end dffSync;	
architecture rtl of dffSync is
begin	
	process(clk)  --同步复位敏感信号表不需要复位信号
	begin
		if(clk'EVENT and clk='1')then
			if (clr_n='0')then
				q<='0';
			else
				q<=d;
			end if;
		end if;	  
	end process;
end rtl;

T触发器

library ieee;
use ieee.std_logic_1164.all;
entity tff is 
	port(clk:in std_logic;
	q:out std_logic);
end tff;  

architecture rtl of tff is 
signal temp:std_logic:='0';
begin 
	process(clk)
	begin	
		if(clk'EVENT and clk='1')then
			temp<=not temp;
		end if;
	end process;	
	q<=temp;
end rtl;

RS触发器

--rs触发器
library ieee;
use ieee.std_logic_1164.all;
entity rsff is
	port(r,s:in std_logic;
	q,qn:out std_logic);
end rsff;
architecture rtl of rsff is	 
signal qtemp,qntemp:std_logic;
begin 	
	qtemp<=r nor qntemp;
	qntemp<=qtemp nor s;
	q<=qtemp;
	qn<=qntemp;
end rtl;

八位寄存器

--8位锁存寄存器
library ieee;
use ieee.std_logic_1164.all;
entity register8 is
	port(clk,reset_n:in std_logic;
	d:in std_logic_vector(7 downto 0);
	q:out std_logic_vector(7 downto 0));
end register8;

architecture rtl of register8 is		 
signal qtemp:std_logic_vector(7 downto 0);
begin
	process(clk,reset_n)
	begin		
		if(reset_n='0')then
			qtemp<="00000000";
		elsif (clk'EVENT and clk='1')then
			q<=qtemp;
		end if;
	end process;
	q<=qtemp;
end rtl;

6位串入串出移位寄存器

library ieee;
use ieee.std_logic_1164.all;

entity siso6 is 
	port(d,clk:in std_logic;
		q:out std_logic);
end siso6;

architecture rtl of siso6 is 
	component dff	  
		port(d,clk:in std_logic;
			q:out std_logic);
	end component;
	signal z:std_logic_vector(0 to 6);
begin  	 
	z(0)<=d;
	g:for i in 0 to 5 generate
	    dff_map: dff
		port map(
		d=>z(i),
		clk=>clk,
		q=>z(i+1)
		);
	end generate;
	q<=z(6);
end rtl;

上面的程序调用的D触发器写在下面

library ieee;
use ieee.std_logic_1164.all;

entity dff is
	port(d,clk:in std_logic;
		q:out std_logic);
end dff;				  
architecture rtl of dff is
begin
	process(clk)
	begin	   
		if clk'EVENT and clk='1' then
			q<=d;
		end if;
	end process;
end rtl;

另一种行为级写法

library ieee;
use ieee.std_logic_1164.all;

entity siso6_v2 is
	port(d,clk:in std_logic;   
	
	q,qn:out std_logic);
end siso6_v2;	

architecture rtl of siso6_v2 is	   
signal temp:std_logic_vector(5 downto 0);  
signal temp1:std_logic_vector(5 downto 0);
begin
        --这一段是为了比较
	process(clk)
	begin		
		if clk'EVENT and clk='1' then	
			temp(4 downto 0)<=temp(5 downto 1);	
			temp(5)<=d;				
		end if;	
	end process;  
        --保留下面这段即可
	process(clk)
	begin		
		if clk'EVENT and clk='1' then	
			temp1(5)<=d;
			temp1(4 downto 0)<=temp1(5 downto 1);							
		end if;	
	end process;   
	qn<=temp1(0);
	q<=temp(0);
end rtl;

十进制计数器

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity count10en is
	port(clk,clr,en:in std_logic;
	qa,qb,qc,qd:out std_logic);
end count10en;				  
architecture rtl of count10en is	
	signal count:std_logic_vector(3 downto 0)  ;
begin 				
	process(clk,clr)
	begin 
		if(clr='1')then
			count<="0000"; 
		elsif clk'EVENT and clk='1' then
			if en='1' then
				if(count="1001")then
					count<="0000";
				else 
					count<=count+1;
				end if;
			end if;
		end if;
	end process;
	qa<=count(0);
	qb<=count(1);
	qc<=count(2);
	qd<=count(3);
end rtl;

可逆计数器

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity countReversible is
port(clk,clr,updown:in std_logic;
qa,qb,qc,qd:out std_logic);
end countReversible;

architecture rtl of countReversible is	
signal count:std_logic_vector(3 downto 0);
begin									   
	process(clk)
	begin
		if(clr='1')then
			count<="0000";
		elsif(clk'EVENT and clk='1')then
			if(updown='1')then
				count<=count+1;
			else
				count<=count-1;
			end if;
		end if;
		
	end process;
	
	qa<=count(0);
	qb<=count(1);
	qc<=count(2);
	qd<=count(3);
end rtl;

6分频器

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity clk_div6 is 
	port(clk,clr:in std_logic;
	clk_div6:out std_logic);
end clk_div6;

architecture rtl of clk_div6 is	 
signal count:std_logic_vector(1downto 0);
signal clk_temp:std_logic;

begin				   
	process(clk,clr)
	begin
		if(clr='1')then
			count<="00";
			clk_temp<='0';
		elsif clk'EVENT and clk='1' then
			if count="10" then
				count<="00";
				clk_temp<=not clk_temp;
			else
				count<=count+1;
			end if;
		end if;
	end process;
	clk_div6<=clk_temp;
	
end rtl;

数控N分频

library IEEE;
use IEEE.STD_LOGIC_1164.all;
use IEEE.STD_LOGIC_UNSIGNED.all;

entity ClkDiv is
    port(
    clk_i:IN STD_LOGIC;
    N_i:  IN STD_LOGIC_VECTOR(9 DOWNTO 0);
    clk_o:OUT STD_LOGIC);
end ClkDiv;

architecture behavior of ClkDiv is
signal count:STD_LOGIC_VECTOR(9 DOWNTO 0):="0000000001";
signal clk_temp:STD_LOGIC:='0';
begin
    process(clk_i)
    begin
        if(clk_i'EVENT and clk_i='1')then  
            if (count=N_i)then
                count<="0000000001";
                clk_temp<='1';
            else
                count<=count+1;
                clk_temp<='0';
            end if;
        end if;
    end process;    
    clk_o<=clk_temp;
end behavior;

状态机

要点是：两定义三进程

1. 状态寄存器描述：clk,rst
2. 下一状态描述：current_state,X
3. 输出描述：current_state

	--引入状态编码的两定义
	constant s0:std_logic_vector(1 downto 0):="00";
	constant s1:std_logic_vector(1 downto 0):="01";
	constant s2:std_logic_vector(1 downto 0):="11";
	
	signal current_state:std_logic_vector(1 downto 0);
	signal next_state:std_logic_vector(1 downto 0);
        --一般的两定义
	type state_type is (S0,S1,S2,S3,S4);
	signal current_state,next_state:state_type;
	

moore机

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity moore is 
	port(clk,rst,X:in std_logic;
		Z:out std_logic);
end moore;		   

architecture behavior of moore is
	type state_type is (S0,S1,S2,S3);
	signal current_state,next_state:state_type;
begin 
	--状态寄存器描述
	sync:process(clk,rst)
	begin		
		if clk'EVENT and clk='1' then 
			if rst='1' then
				current_state<=S1;
			else
				current_state<=next_state;
			end if;
		end if ;
	end process; 
	
	--下一转态描述
	state_trans:process(current_state,X)
	begin		
		case current_state is 
			when S0=>
				if X='0' then
					next_state<=S0;
				else 
					next_state<=S2;	
				end if;
			when S1=>
				if X='0' then
					next_state<=S0;
				else 
					next_state<=S2;	
				end if;	
			when others=>
				next_state<=S1;
		end case;
	end process; 
	
	--输出描述
	output:process(current_state)
	begin		
		case current_state is 
			when S0=>Z<='0';
			when S1=>Z<='1';
			when others=>Z<='0';
		end case;
	end process;
	
end behavior ;

mealy机

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity mealy is
	port(clk,clr,X:in std_logic;
		Z:out std_logic);
end mealy;			

architecture rtl of mealy is 
	type state_type is (S0,S1,S2,S3);
	signal current_state,next_state:state_type;
begin 
	--寄存器描述
	sync:process(clk,clr,next_state)
	begin		
		if clk'EVENT and clk='1' then
			if clr='1' then
				current_state<=S0;
			else
				current_state<=next_state;
			end if;
		end if;
	end process;  
	
	--下一状态描述、输出描述
	combin:process(current_state,X)
	begin
		case current_state is 
			when S0=>
				if X='0'then
					next_state<=S0;
					Z<='1';
				else
					next_state<=S1;
					Z<='0';
				end if;
			
			when others=>
				next_state<=S0;
				Z<='0';
		end case;	
	end process;
end rtl;

testbench

library ieee;
use ieee.std_logic_1164.all;

entity siso6_v2_tb is
end siso6_v2_tb;

architecture TB_ARCHITECTURE of siso6_v2_tb is
	component siso6_v2
	port(
		d : in STD_LOGIC;
		clk : in STD_LOGIC;
		q,qn : out STD_LOGIC );
	end component;

	signal d : STD_LOGIC;
	signal clk : STD_LOGIC;
	signal q ,qn: STD_LOGIC;
begin

	UUT : siso6_v2
		port map (
			d => d,
			clk => clk,
			q => q ,
			qn => qn
		); 
	
--时钟	
	process
	begin 	   
		clk<='1';
		wait for 50ns;
		clk<='0';
		wait for 50ns ;
	end process	;	   
	
	d<='1',
	'0' after 1000ns,
	'1' after 1200ns,
	'0' after 1300ns,
	'1' after 1500ns;
							
end TB_ARCHITECTURE;