VHDL实现矩阵键盘检测
矩阵键盘相比独立键盘，其实就是起到节约IO口的作用，尤其在需要多个按键的时候。原理图（摘自其他地方）：
比如0键，没按下时，ROW0因为上拉而为高电平。当0按下时，如果此时COL0为低电平，则ROW0为低电平。因此矩阵键盘就是要让几列（或行）轮流置零，并检测行（或列）的电平高低，从而确定某一按键是否按下。这就是扫描过程。
以下是VHDL代码：
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity matrix is
port(clk: in std_logic;
row: in std_logic_vector(3 downto 0);
col: out std_logic_vector(3 downto 0);
keyout: out std_logic_vector(3 downto 0);
flag: out std_logic);
end matrix;
architecture behave of matrix is
signal colreg: std_logic_vector(3 downto 0);
signal con: std_logic_vector(7 downto 0);
signal cnt: std_logic_vector(15 downto 0);
signal clkreg: std_logic;
begin
--分频，在1~10KHZ左右的时钟进行键盘扫描--
process(clk)
begin
if clk'event and clk = '1' then
if cnt = "1100001101001111" then
cnt<="0000000000000000";
clkreg<='0';
else if cnt = "0110000110100111" then
cnt<=cnt+"0000000000000001";
clkreg<='1';
else
cnt<=cnt+"0000000000000001";
end if;
end if;
end process;
--产生列扫描信号--
process(clkreg)
begin
if clkreg'event and clkreg = '1' then
case colreg is
when "1110" => colreg<="1101";
when "1101" => colreg<="1011";
when "1011" => colreg<="0111";
when "0111" => colreg<="1110";
when others => colreg<="1110";
end case;
end if;
end process;
--对行信号和列信号进行组合--
col<=colreg;
con<= colreg & row;
--对组合的扫描信号进行判断，并输出按键指示信号以及编码--
process(clkreg)
begin
if clkreg'event and clkreg = '1' then
case con is
when "11101110" => keyout<="0000";flag<='1';
when "11011110" => keyout<="0001";flag<='1';
when "10111110" => keyout<="0010";flag<='1';
when "01111110" => keyout<="0011";flag<='1';
when "11101101" => keyout<="0100";flag<='1';
when "11011101" => keyout<="0101";flag<='1';
when "10111101" => keyout<="0110";flag<='1';
when "01111101" => keyout<="0111";flag<='1';
when "11101011" => keyout<="1000";flag<='1';
when "11011011" => keyout<="1001";flag<='1';
when "10111011" => keyout<="1010";flag<='1';
when "01111011" => keyout<="1011";flag<='1';
when "11100111" => keyout<="1100";flag<='1';
when "11010111" => keyout<="1101";flag<='1';
when "10110111" => keyout<="1110";flag<='1';
when "01110111" => keyout<="1111";flag<='1';
when "11101111" => flag<='0';
when "11011111" => flag<='0';
when "10111111" => flag<='0';
when "01111111" => flag<='0';
end case;
end if;
end process;
end behave;