library ieee;
use ieee.std_logic_1164.all;

entity key_scan is
 port (
        clk    : in  std_logic;
        keyin  : in  std_logic_vector(3 downto 0);   --4*4键盘扫描4输入
        keyout : out std_logic_vector(3 downto 0);   --4*4键盘扫描4输出
        numb   : out std_logic_vector(6 downto 0)           --输出键值，
       );
end key_scan;

architecture rtl of key_scan is
signal code     : std_logic_vector(7 downto 0);
signal countA   : integer range 0 to 3;        --以计数的方式产生扫描信号
signal scn      : std_logic_vector(3 downto 0);
begin

code   <= scn&keyin;
keyout <= scn;

process(clk)
begin
 if clk 'event and clk = '1' then         --产生扫描信号
   if countA = 3 then
     countA <= 0;
   else
     countA <= countA + 1;
   end if;
   case countA is
     when 0      => scn <= "1110";
     when 1      => scn <= "1101";
     when 2      => scn <= "1011";
     when 3      => scn <= "0111";
     when others => scn <= "1111";
   end case;
 end if;
end process;

process(clk)
begin
 if clk 'event and clk = '0' then     -- 上升沿产生扫描信号，下降沿读入键码
      case code is
        when  "01111110" => numb <= "0111111" ; -- X"3F"'0
        when  "01111101" => numb <= "0000110" ; -- X"06"'1
        when  "01111011" => numb <= "1011011" ; -- X"5B"'2
        when  "01110111" => numb <= "1001111" ; -- X"4F"'3
        when  "10111110" => numb <= "1100110" ; -- X"66"'4
        when  "10111101" => numb <= "1101101" ; -- X"6D"'5
        when  "10111011" => numb <= "1111101" ; -- X"7D"'6
        when  "10110111" => numb <= "0000111" ; -- X"07"'7
        when  "11011110" => numb <= "1111111" ; -- X"7F"'8
        when  "11011101" => numb <= "1101111" ; -- X"6F"'9
        when  "11011011" => numb <= "1110111" ; -- X"77"'10
        when  "11010111" => numb <= "1111100" ; -- X"7C"'11
        when  "11101110" => numb <= "0111001" ; -- X"39"'12
        when  "11101101" => numb <= "1011110" ; -- X"5E"'13
        when  "11101011" => numb <= "1111001" ; -- X"79"'14
        when  "11100111" => numb <= "1110001" ; -- X"71"'15
        when  others     => NULL;
      end case;
  end if;
 end process;

end rtl;