write_to_24c02.vhd

是一些很好的FPGA设计实例

--文件名：write_to_24c02.vhd

--功  能：将数据写入存储芯片24c02中

--说  明：程序设计中使用了状态机，在写的时候变化到每个状态均点亮相应的二极管，

--使我们能一目了然的看到状态的变化以及何时写成功，在点亮最左边的二极

--管时，表示写成功；该程序写入的数据是7，操作的从机地址是第三单元，对

--数据写入的地址单元用户可以通过改变从机地址sub_address来修改，数据

--的设置用户也可以通过改写程序中的data的数据来自行设置。

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;  --写成功

entity write_to_24c02 is
    Port ( sysclk,reset : in std_logic;
           sda,scl : inout std_logic;
		 cs: out std_logic; 
		 s:out std_logic_vector(7 downto 0)        
          );
end write_to_24c02;
architecture Behavioral of write_to_24c02 is
type state is (prepare,start,transmit_slave_address,check_ack1,transmit_sub_address,check_ack2,
transmit_data,check_ack3,stop,idel);     --定义状态机的各子状态；
signal current_state:state;                         --定义信号；
signal clock:std_logic;

begin
pulse:process(sysclk,reset)                    --进程1，分频得到周期为0.1s的时钟信号
variable count:integer range 0 to 5000000;
begin
   if reset='0' then count:=0;
	  elsif rising_edge(sysclk) then
	    count:=count+1;
       if count=2500000 then clock<='1';
		   elsif count=5000000 then clock<='0';count:=0;    --frequency:10Hz time:0.1s
		   end if;
	  end if;
end process pulse;
statemachine:process(clock,reset)               --进程2，状态机的转换
variable slave_address,sub_address,data:std_logic_vector(8 downto 1);
variable cnt:std_logic_vector(6 downto 0);
variable cnt1:integer range 0 to 8;
variable count1:integer range 0 to 40;

begin
if  reset='0'  then  count1:=0;cnt:="0000000";cnt1:=8;cs<='1';
sda<='1';scl<='1';slave_address:="10100000";sub_address:="00000011";
current_state<=prepare;data:="00000111";
s<="11111111";
   	elsif rising_edge(clock) then  
	 case current_state is
	 when prepare=>cnt:=cnt+1;--    --准备状态，等各个器件复位
	      if cnt="0000010" then cnt:="0000000";current_state<=start;
	   	 else current_state<=prepare;
		  end if;
	 when start=>count1:=count1+1;        --起始信号产生状态
	                    case count1 is
				    when 1=>sda<='1';
				    when 2=>scl<='1';
				    when 3=>sda<='0';
				    when 4=>scl<='0';
				    when 5=>count1:=0;current_state<=transmit_slave_address;
				    when others=>null;
				    end case;
	 when transmit_slave_address=>count1:=count1+1;s<="01111111";  --发送器件从地址
	                     case count1 is
				    when 1=>sda<=slave_address(cnt1);
				    when 2=>scl<='1';
				    when 3=>scl<='0';
				    when 4=>cnt1:=cnt1-1;count1:=0;
					  if cnt1=0 then cnt1:=8;
					  current_state<=check_ack1;
					  else current_state<=transmit_slave_address;
					  end if;
				    when others=>null;
				    end case;
	 when check_ack1=>count1:=count1+1;s<="10111111";          --查询应答信号
	                     case count1 is
				    when 1=>sda<='0';
				    when 2=>scl<='1';
				   
				    when 3=>scl<='0';
				    				    				    
				    when 4=>
				          current_state<=transmit_sub_address;
						  
						  count1:=0;
				    when others=>null;
				    end case;
       when transmit_sub_address=>count1:=count1+1;s<="11011111";  --发送器件子地址
	                     case count1 is				   
				    when 1=>sda<=sub_address(cnt1);
				    when 2=>scl<='1';
				    when 3=>scl<='0';
				    when 4=>cnt1:=cnt1-1;count1:=0;
					  if cnt1=0 then cnt1:=8;
					  current_state<=check_ack2;
					  else current_state<=transmit_sub_address;
					  end if;
				    when others=>null;
				    end case;
	 when check_ack2=>count1:=count1+1; s<="11101111";         --查询应答信号
	                     case count1 is
				    when 1=>sda<='0';
				    when 2=>scl<='1';				    
				    when 3=>scl<='0';				   				    				    
				    when 4=>current_state<=transmit_data;
			                 count1:=0;
				    when others=>null;
				    end case;
	 when transmit_data=>count1:=count1+1;s<="11110111";  --发送数据
	                     case count1 is				    
				    when 1=>sda<=data(cnt1);
				    when 2=>scl<='1';
				    when 3=>scl<='0';
				    when 4=>cnt1:=cnt1-1;count1:=0;
					  if cnt1=0 then cnt1:=8;
					  current_state<=check_ack3;
					  else current_state<=transmit_data;
					  end if;
				    when others=>null;
				    end case;
	 when check_ack3=>count1:=count1+1;s<="11111011";          --查询应答信号
	                     case count1 is
					when 1=>sda<='0';
				    when 2=>scl<='1';
				    
				    when 3=>scl<='0';
				    			    				    
				    when 4=>
				          current_state<=stop;
						 
						  count1:=0;
				    when others=>null;
				    end case;
	when stop=>count1:=count1+1; s<="11111101";   --产生停止信号
	                           case count1 is
				          when 1=>sda<='0';
				          when 3=>scl<='1';
				          when 10=>sda<='1';
   			              when 15=>count1:=0;current_state<=idel;
				          when others=>null;
				          end case;
	when idel=>sda<='1';scl<='1';current_state<=idel;	s<="11111110";							 
     when others=>null;
    end case;
  end if;
 end process;
end Behavioral;