keyboard4_4.vhd

该代码是4乘4标准键盘扫描程序的源代码

--******************************************************************
--* 4x4标准键盘板读取并点亮开发板上相应led
--* Filename: keyboard4_4
--* 扫描键盘，译码并点亮开发板上相应led
--* 尚未仔细考虑一些细节问题，譬如防颤等
--******************************************************************

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use ieee.std_logic_unsigned.all;
entity keyboard4_4 is
    port(
        rst        :    in    std_logic;
        clk        :    in    std_logic;
        keyin    :    in    std_logic_vector(3 downto 0);
        scan    :    out    std_logic_vector(3 downto 0);
        leds    :    out    std_logic_vector(3 downto 0)
    );
end keyboard4_4;

architecture keyboard4_4_arch of keyboard4_4 is
    signal clkfrq    :    std_logic;
    signal cntscn    :    std_logic_vector(1 downto 0);
    signal scnlin    :    std_logic_vector(3 downto 0);
    --signal cntfrq    :    std_logic_vector(14 downto 0);
    signal cntfrq   :       std_logic_vector(3 downto 0);
    signal lednum    :    std_logic_vector(7 downto 0);

begin
    process(rst,clk) -- 晶振为50MHz，进行25000分频产生扫描时钟（1000Hz)
    begin
        if rst = '0' then
            clkfrq <= '0';
            cntfrq <= (others => '0');
        elsif clk'event and clk = '1' then
           -- if cntfrq = "110000110101000" then 
            if cntfrq = "1111" then 
                cntfrq <= (others => '0');
                clkfrq <= not clkfrq;
            else
                cntfrq <= cntfrq + 1;
            end if;
        end if; 
    end process;
    
    process(rst,clkfrq)    -- 根据扫描时钟产生扫描线    
    begin
        if rst = '0' then
            cntscn <= "00";
        elsif clkfrq'event and clkfrq = '1' then
            if cntscn = "11" then
                cntscn <= "00";
            else
                cntscn <= cntscn+1;
            end if;
            case cntscn is
                when "00" => scnlin <= "0001";
                when "01" => scnlin <= "0010";
                when "10" => scnlin <= "0100";
                when "11" => scnlin <= "1000";
                when others => null;
            end case;
        end if;        
    end process;            
    
    process(rst, clkfrq) -- 根据按键点亮相应的leds
    begin
        if(rst = '0' ) then
            leds <= "1111";
        elsif clkfrq'event and clkfrq = '0' then
            case lednum is
                when "00010001" =>
                    leds <= "0000";
                when "00010010" =>
                    leds <= "0001";
                when "00010100" =>
                    leds <= "0010";
                when "00011000" =>
                    leds <= "0011";
                    
                when "00100001" =>
                    leds <= "0100";
                when "00100010" =>
                    leds <= "0101";
                when "00100100" =>
                    leds <= "0110";
                when "00101000" =>
                    leds <= "0111";
                                    
                when "01000001" =>
                    leds <= "1000";
                when "01000010" =>
                    leds <= "1001";
                when "01000100" =>
                    leds <= "1010";
                when "01001000" =>
                    leds <= "1011";    
                    
                when "10000001" =>
                    leds <= "1100";
                when "10000010" =>
                    leds <= "1101";
                when "10000100" =>
                    leds <= "1110";
                when "10001000" =>
                    leds <= "1111";    
                
                when others =>    null;
            end case;
        end if;
    end process;
    
    scan <= scnlin;
    lednum <= scnlin&keyin;
    
end keyboard4_4_arch;