--文件名：dac0832.vhd

--功  能：0～5伏可調數字電壓源

--說  明：1.這里是以5伏為基準電壓

--        2.通過八位撥盤開關對當前的電壓進行數字設定

--        3.數碼管顯示當前電壓值

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity dac0832 is
    Port (clk : in std_logic;
	     datin : in std_logic_vector(7 downto 0);
		shift : out std_logic_vector(3 downto 0);
		dout_0832  : out std_logic_vector(7 downto 0);
		dout_led : out std_logic_vector(7 downto 0);
		cs_led : out std_logic_vector(1 downto 0);
	     wr,cs:out std_logic);
end dac0832;

architecture Behavioral of dac0832 is

type states is (st0,st1);              			
signal state:states:=st0;                      

type state1 is (st0,st1,st2);
signal current_state1 : state1; 

type state2 is (st0,st1,st2,st3,st4);
signal current_state2 : state2; 

signal reg_dout : std_logic_vector(15 downto 0);
signal dout : std_logic_vector(4 downto 0);

signal clk100k,clk1k,clk100 : std_logic;
begin

dout_0832<=datin;

--系統分頻
process(clk)
variable cnt : integer range 0 to 500; --產生100KHz的頻率；
begin
   if rising_edge(clk) then cnt:=cnt+1;
	 if cnt<250 then clk100k<='0';
	 elsif cnt<500 then clk100k<='1';
	 else cnt:=0;clk100k<='0';
	 end if;
   end if;
end process;

process(clk100k)
variable cnt: integer range 0 to 100; --產生1KHz的頻率；
begin
   if rising_edge(clk100k) then cnt:=cnt+1;
      if cnt<50 then clk1k<='0';
	 elsif cnt<100 then clk1k<='1';
	 else cnt:=0;clk1k<='0';
	 end if;
   end if;
end process;

process(clk1k)
variable cnt : integer range 0 to 10;--產生100Hz的頻率；
begin
   if rising_edge(clk1k) then cnt:=cnt+1;
      if cnt<5 then clk100<='0';
	 elsif cnt<10 then clk100<='1';
	 else cnt:=0;clk100<='0';
	 end if;
   end if;
end process;

--dac0832的控制程序
process(clk100k)
begin
   if rising_edge(clk100k) then
      case state is                                                          --狀態之間的轉換
	   when st0=>wr<='1'; cs<='1'; state<=st1;
	   when st1=>wr<='0'; cs<='0'; state<=st0;
	   when others=>null;
	 end case;	 
   end if;
end process; 

--十進制－BCD碼轉換；
process(clk100)		   
variable reg : integer range 0 to 8000;
variable d1,d2,d3,d4 : std_logic_vector(3 downto 0);
begin
   if clk100'event and clk100='1' then
      case current_state1 is
	 when st0=>
	           reg:=conv_integer(datin)*20;  --將輸入的二進制信號轉換成十進制再乘以電壓系數＝當前電壓值
			 d1:="0000";d2:="0000";d3:="0000";d4:="0000";
			 current_state1<=st1;
      when st1=>
	           if reg>999 then reg:=reg-1000;d1:=d1+1;
			 elsif reg>99 then reg:=reg-100;d2:=d2+1;
			 elsif reg>9 then reg:=reg-10;d3:=d3+1;
			 elsif reg>0 then reg:=reg-1;d4:=d4+1;
			 else current_state1<=st2;
			 end if;
      when st2=>
			 reg_dout<=d1&d2&d3&d4;
			 current_state1<=st0;
      when others=> 
	           current_state1<=st0;
      end case;
   end if;
end process;

--動態掃描控制；
process(clk1k)
begin
   if clk1k'event and clk1k='1' then
      case current_state2 is
      when st0=>							 --熄滅與本實驗無關的發光二極管
                cs_led<="11";
			 shift<="1111";                     
			 dout<="11111";
                current_state2<=st1;
      when st1=>							 --在數碼管的最高位顯示數據
	           cs_led<="10";
			 shift<="0111";
			 dout<='0'&reg_dout(15 downto 12);
			 current_state2<=st2;
      when st2=>							 --在數碼管的次高位顯示數據
	           cs_led<="10";
			 shift<="1011";
			 dout<='1'&reg_dout(11 downto 8);
			 current_state2<=st3;
	 when st3=>							 --在數碼管的次低位顯示數據
	           cs_led<="10";
			 shift<="1101";
			 dout<='1'&reg_dout(7 downto 4);
			 current_state2<=st4;
      when st4=>							 --在數碼管的最低位顯示數據
	           cs_led<="10";
			 shift<="1110";
			 dout<='1'&reg_dout(3 downto 0);
			 current_state2<=st1;
      when others=>
	           current_state2<=st0;
	 end case;
   end if;
end process;

--將BCD碼進行8段譯碼（包括小數點）
code1: process (dout)                       
begin
   case dout(3 downto 0) is
   when "0000"=>dout_led<=dout(4)&"0000001";--dout（4）代表小數點，低電平點亮
   when "0001"=>dout_led<=dout(4)&"1001111";
   when "0010"=>dout_led<=dout(4)&"0010010";
   when "0011"=>dout_led<=dout(4)&"0000110";
   when "0100"=>dout_led<=dout(4)&"1001100";
   when "0101"=>dout_led<=dout(4)&"0100100";
   when "0110"=>dout_led<=dout(4)&"0100000";
   when "0111"=>dout_led<=dout(4)&"0001111";
   when "1000"=>dout_led<=dout(4)&"0000000";
   when "1001"=>dout_led<=dout(4)&"0000100";
   when others=>dout_led<="11111111";
   end case;
end process;  
end Behavioral;