VHDL键盘代码问题

Question

我有一个4x3键盘，我写这个FSM用于连接我的Nexys2板，我遇到的麻烦是

1. 当我运行代码时，LED会在没有按任何键的情况下发光，它会自动显示随机组合

2. 当我按下一个键时，它会显示特定的组合，然后在没有按任何键的情况下进入ROW的下一个条件。有时，如果按一个键，它甚至不会响应。

发生了什么事？这段代码有什么问题？我很无能为力。有人可以指出错误并提出一些解决方案吗？这是我的代码

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;


entity keypad_3x4 is
     Port ( CLK     : in  STD_LOGIC;
              RESET     : in  STD_LOGIC;
              ROW   : in  STD_LOGIC_VECTOR (3 downto 0);
              COL   : out STD_LOGIC_VECTOR (2 downto 0);
              LED       : out STD_LOGIC_VECTOR (3 downto 0)
              );
end keypad_3x4;


architecture Behavioral of keypad_3x4 is
architecture Behavioral of keypad_3x4 is


 TYPE STATE_TYPE is
    (   RESET_ST,
        S1,
        S2,
        S3,
        S4,
        S5,
        S6
    );

signal  state:  STATE_TYPE;
begin

 process (CLK, RESET)
 begin

    if  (RESET = '1') then
        state       <= RESET_ST;    
    elsif   (CLK'event and CLK = '1') then

    case (state) is 

    WHEN RESET_ST       =>
            LED             <= (others => '0');
            COL         <= (others => '0');
            state           <= S1;

    WHEN S1         =>
        COL             <= "001";       --C1 selected
        LED             <= (others => '0');
        state           <= S2;

    WHEN S2         =>
        if  ROW         <= "0001" then
                led         <= "0001";  --1     
        elsif ROW       <= "0010" then
                led         <= "0100";  --4     
        elsif ROW       <= "0100" then
                led         <= "0111";  --7     
        elsif ROW       <= "1000" then
                led         <= "1111";  --*     
        else
                LED         <= (others => '0');
                state       <= S3;
        end if;

    WHEN S3         =>
        COL             <= "010";       --C2 selected
        LED         <= (others => '0');
        state           <= S4;

    WHEN S4     =>
        if  ROW <= "0001" then
                led <= "0010";  --2 
        elsif ROW <= "0010" then
                led <= "0101";  --5     
        elsif ROW <= "0100" then
                led <= "1000";  --8
        elsif ROW <= "1000" then
                led <= "0000";  --0
        else
                LED         <= (others => '0');
                state       <= S5;
        end if;

    WHEN S5     =>
        COL             <= "100";       --C3 selected
        LED             <= (others => '0');
        state           <= S6;

    WHEN S6     =>
        if  ROW <= "0001" then
                led <= "0011";  --3
        elsif ROW <= "0010" then
                led <= "0110";  --6
        elsif ROW <= "0100" then
                led <= "1001"; --9
        elsif ROW <= "1000" then
                led <= "1111";  --#
        else
                LED         <= (others => '0');
                state       <= RESET_ST;
        end if;

    WHEN others =>
                state       <= RESET_ST;    
    END case;
END if;
END process;

end Behavioral;