entity dds is
  --generic(mul_32:std_logic_vector(31 downto 0):="10101011110011000111011100010001");
    Port ( clk : in  STD_LOGIC;                      --系统时钟
--  reset : in std_logic;
--  channel : in std_logic_vector(1 downto 0);     --输入频率值切换分别为：一般，输入最小值，输入步进，输入最大值
--  fre_data: in std_logic_vector(25 downto 0);    --输入26位频率值
    dds_wclk: out std_logic;                       --输出控制时钟信?
    dds_fqud: buffer std_logic;                    --输出控制频率转换信?
    dds_data: out std_logic_vector( 7 downto 0);   --DDS八位数据端口 
  dds_reset:out std_logic:='0');               --DDS复位信号
end dds;

architecture Behavioral of dds is
 SIGNAL clkdiv  : std_logic:='0';                   ---分频后时钟
 signal data_reg: std_logic_vector(39 downto 0);   --40位控制字寄存器
 signal stat:std_logic_vector(3 downto 0):="0000";    
-- signal add_data:std_logic_vector(25 downto 0);     --频率增量 
-- signal dds_data_max:std_logic_vector(25 downto 0); --频率最大扫描范围
-- signal dds_data_min:std_logic_vector(25 downto 0); --频率最小扫描范围
 signal dds_datain:std_logic_vector(25 downto 0); --输出频率值：
 signal dds_data_32:std_logic_vector(31 downto 0); --输出频率值的控制字

-------------------------------------------------------------------------------
 --控制字转换函数，将26位输入频率值转换为32位频率控制字
-------------------------------------------------------------------------------
  function mul26_to32(data:std_logic_vector)
   return std_logic_vector is
   variable mul_full58:std_logic_vector(57 downto 0);
   variable phase_32:std_logic_vector(31 downto 0);
  begin
   mul_full58:=data * "10101011110011000111011100010001";
   ---------"10101011110011000111011100010001"频率控制字公式计算中间值
   phase_32:=mul_full58(57 downto 26);
   return phase_32;
  end mul26_to32;
-----------------------------------------------------------------------------------------
begin
 dds_datain<="00100110001001011010000000"; 

 dds_data_32<=mul26_to32(dds_datain); --调用函数，豢刂谱?
 data_reg(39 downto 0)<="00000000" & dds_data_32(31 downto 0);
------------------------------------------------------------------------------------------ 
-- process (reset,channel,fre_data)
-- begin
--  if reset='1' then     --全扫描，频率范围300~10M，步进：10K
--   dds_data_min<="00000000000000000100101100"; 
--   add_data<="00000000000000001111101000"; 
--   dds_data_max<="00100110001001011010000000"; 
--  else
--   case channel is    
--   when "00"=> dds_data_min<=fre_data;   --输入频率值下限
--   when "01"=> dds_data_max<=fre_data;   --输入德手瞪舷?
--   when "10"=> add_data<=fre_data;     --输入频率值步进
--   when others => null;
--   end case;
--  end if;
-- end process;
-------------------------------------------------------------------------------------- 
 PROCESS (clk)------------------------------n1分频
     variable n1:integer range 0 to 16;   
      BEGIN
       IF (clk' event AND clk='1') THEN      
        IF (n1 = 16) THEN
         n1 := 0;
         clkdiv <=NOT clkdiv;   
        ELSE
         n1 := n1 + 1;    
        END IF;
       END IF;
      END PROCESS;
------------------------------------------------------------------------------------
 PROCESS(clkdiv)
 variable count:integer range 0 to 1000;  ---控制延时时间   
 BEGIN
  IF clkdiv'EVENT AND clkdiv='1' THEN 
   case stat is
   when "0000"=>dds_reset<='1'; stat<="0001"; --复位操作
   when "0001"=>dds_reset<='0'; dds_fqud<='0'; dds_wclk<='0'; stat<="0010";
    --初始化DDS，以下为写频率控制字-----------------------------------------
   when "0010"=>dds_data<=data_reg(39 DOWNTO 32); dds_wclk<='0'; STAT<="0011";
   when "0011"=>dds_wclk<='1'; STAT<="0100";  --上升沿写入刂谱郑甙宋幌辔豢刂谱?   when "0100"=>dds_data<=data_reg(31 DOWNTO 24); dds_wclk<='0'; STAT<="0101";
   when "0101"=>dds_wclk<='1'; STAT<="0110";  --依次将32位频率控制字写入
   when "0110"=>dds_data<=data_reg(23 DOWNTO 16); dds_wclk<='0'; STAT<="0111";
   when "0111"=>dds_wclk<='1'; STAT<="1000";
   when "1000"=>dds_data<=data_reg(15 DOWNTO 8);  dds_wclk<='0'; STAT<="1001";
   when "1001"=>dds_wclk<='1'; STAT<="1010";
   when "1010"=>dds_data<=data_reg(7 DOWNTO 0);   dds_wclk<='0'; STAT<="1011";
   when "1011"=>dds_wclk<='1'; STAT<="1100";
   when "1100"=>dds_wclk<='0';dds_fqud<='1'; STAT<="1101";
    --控制字写入，FQUD上升沿所存到DDS中-------------------------------------
   when "1101"=>dds_fqud<='0';count:=count+1; --频率转换间的延时，COUNT个时钟
    if (count=1000) then  count:=0; STAT<="0010";
    else null; end if;
   when others=>null;
   end case;
  END IF;
 END PROCESS;
-------------------------------------------------------------------------------------
 --控制扫频范围在300HZ~50M之?
-- process(dds_fqud)
-- begin
--  if dds_fqud'event and dds_fqud='1' then
--   if dds_datain > dds_data_max then     --输出频率值最大限度，设9850时钟德?00M
--    dds_datain<=dds_data_min;           --赋值频率最小范围
--   else 
--    dds_datain<=dds_datain+add_data;
--   end if;
--  end if;
-- end process;
------------------------------------------------------------------------------------------
end Behavioral;