用vhdl语言生成一个4*4矩阵键盘扫描

下面是一个简单的 VHDL 代码实现，用于生成一个 4x4 的矩阵键盘扫描器：

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

entity keypad is
    Port (
        row : inout std_logic_vector(3 downto 0);    -- 行信号
        col : in std_logic_vector(3 downto 0);       -- 列信号
        key : out std_logic_vector(15 downto 0)      -- 按键状态
    );
end keypad;

architecture Behavioral of keypad is
    signal row_int : std_logic_vector(3 downto 0);   -- 内部行信号
    signal col_int : std_logic_vector(3 downto 0);   -- 内部列信号
begin
    -- 行信号输出
    row <= row_int;
    
    -- 列信号输入
    col_int <= col;
    
    -- 按键状态输出
    key(0) <= not(row_int(0)) and not(col_int(0));
    key(1) <= not(row_int(0)) and not(col_int(1));
    key(2) <= not(row_int(0)) and not(col_int(2));
    key(3) <= not(row_int(0)) and not(col_int(3));
    key(4) <= not(row_int(1)) and not(col_int(0));
    key(5) <= not(row_int(1)) and not(col_int(1));
    key(6) <= not(row_int(1)) and not(col_int(2));
    key(7) <= not(row_int(1)) and not(col_int(3));
    key(8) <= not(row_int(2)) and not(col_int(0));
    key(9) <= not(row_int(2)) and not(col_int(1));
    key(10) <= not(row_int(2)) and not(col_int(2));
    key(11) <= not(row_int(2)) and not(col_int(3));
    key(12) <= not(row_int(3)) and not(col_int(0));
    key(13) <= not(row_int(3)) and not(col_int(1));
    key(14) <= not(row_int(3)) and not(col_int(2));
    key(15) <= not(row_int(3)) and not(col_int(3));
    
    -- 行扫描控制
    process(col_int)
    begin
        row_int <= "1110";  -- 初始化为第一行
        wait for 10 ns;     -- 等待一段时间
        row_int <= "1101";  -- 扫描第二行
        wait for 10 ns;     -- 等待一段时间
        row_int <= "1011";  -- 扫描第三行
        wait for 10 ns;     -- 等待一段时间
        row_int <= "0111";  -- 扫描第四行
        wait for 10 ns;     -- 等待一段时间
    end process;
end Behavioral;

该代码使用了一个 `process` 进程来控制行信号的扫描，通过改变 `row_int` 的值来控制行信号的输出，从而实现对矩阵键盘的扫描。同时，还使用了 `wait for` 语句来控制每次扫描的持续时间。最后，通过对 `row_int` 和 `col_int` 的取反运算，实现对按键状态的检测和输出。