//I2C在CPLD上的模擬實現(xiàn)源程序


type clock_type is (s0,s1,s2,s3);
signal state0:clock_type;
signal state1:state_type;
case state is
        when s0=>
          da<=''1'';
          scl<=''1'';
          state<=s1;
        when s1=>
          da<=''1'';
          scl<=''1'';
          state<=s2;
        when s2=>
          da<=''0'';
          scl<=''1'';
          state<=s3;
        when s3=>
          da<=''0'';
          scl<=''0'';
          state<=s0;
          state1<=s_byte;
        when others=>
          state<=s0;
       end case;

//下面是利用case…when語句編寫的移位及輸入、輸出字節(jié)模塊。
inoutdata:block
 signal code:std_logic_vector(2 downto 0);
 begin
process(read,endata,cl)   //cl與scl同步
begin
  code<=read & endata & flag;
  if cl''event and cl=''1''then
   case code is           
     when "010" "011" =>  //從MCU讀入一個要發(fā)送的數(shù)據(jù)
        datain<=data;
     when "001"=>        //8位左移寄存器,將要輸出的位存于data7
        data7<=datain(7);
        datain(0)<=''1'';
        for i in 1 to 7 loop
         datain(i)<=datain(i-1);
        end loop;
     when "101"=>        //將向MCU發(fā)送的數(shù)據(jù)暫存于dataout
        dataout<=data1;
     when "100"=>        //8位右移寄存器,data0為從SDA接收的值
        data1(0)<=data0;
        for i in 1 to 7 loop
         data1(i)<=data1(i-1);
        end loop;
     when others=>
        null;
   end case;
  end if; 
end process;
end block inoutdata;