FPGA数字时钟设计代码，可调整时间功能

以下是一个简单的FPGA数字时钟设计代码，具有可调整时间功能。代码使用VHDL语言编写，使用FPGA板上的时钟信号作为时钟输入，并使用七段数码管显示时间。

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

entity digital_clock is
    Port ( clk : in STD_LOGIC;
           reset : in STD_LOGIC;
           adjust : in STD_LOGIC;
           sevenseg_out : out STD_LOGIC_VECTOR (6 downto 0));
end digital_clock;

architecture Behavioral of digital_clock is

    signal seconds: unsigned(5 downto 0);
    signal minutes: unsigned(5 downto 0);
    signal hours: unsigned(4 downto 0);
    signal count: unsigned(21 downto 0);

begin

    process(clk,reset)
    begin
        if reset = '1' then
            seconds <= (others => '0');
            minutes <= (others => '0');
            hours <= (others => '0');
            count <= (others => '0');
        elsif rising_edge(clk) then
            if count = 1000000 then
                count <= (others => '0');
                seconds <= seconds + 1;
            else
                count <= count + 1;
            end if;

            if seconds = 60 then
                seconds <= (others => '0');
                minutes <= minutes + 1;
            end if;

            if minutes = 60 then
                minutes <= (others => '0');
                hours <= hours + 1;
            end if;

            if hours = 24 then
                hours <= (others => '0');
            end if;

        end if;
    end process;

    process(adjust)
    begin
        if adjust = '1' then
            if seconds = 59 then
                seconds <= (others => '0');
            else
                seconds <= seconds + 1;
            end if;
        end if;
    end process;

    process(seconds, minutes, hours)
    begin
        case seconds is
            when 0 => sevenseg_out <= "0000001";
            when 1 => sevenseg_out <= "1001111";
            when 2 => sevenseg_out <= "0010010";
            when 3 => sevenseg_out <= "0000110";
            when 4 => sevenseg_out <= "1001100";
            when 5 => sevenseg_out <= "0100100";
            when 6 => sevenseg_out <= "0100000";
            when 7 => sevenseg_out <= "0001111";
            when 8 => sevenseg_out <= "0000000";
            when 9 => sevenseg_out <= "0000100";
            when 10 => sevenseg_out <= "0001000";
            when 11 => sevenseg_out <= "1100000";
            when 12 => sevenseg_out <= "0110001";
            when 13 => sevenseg_out <= "1000010";
            when 14 => sevenseg_out <= "0100001";
            when 15 => sevenseg_out <= "0111001";
            when 16 => sevenseg_out <= "0010000";
            when 17 => sevenseg_out <= "0011110";
            when 18 => sevenseg_out <= "0001001";
            when 19 => sevenseg_out <= "0011000";
            when 20 => sevenseg_out <= "0000010";
            when 21 => sevenseg_out <= "0000001";
            when 22 => sevenseg_out <= "0000110";
            when 23 => sevenseg_out <= "0010000";
            when others => sevenseg_out <= "1111111";
        end case;

        case minutes is
            when 0 => sevenseg_out(13 downto 7) <= "0000001";
            when 1 => sevenseg_out(13 downto 7) <= "1001111";
            when 2 => sevenseg_out(13 downto 7) <= "0010010";
            when 3 => sevenseg_out(13 downto 7) <= "0000110";
            when 4 => sevenseg_out(13 downto 7) <= "1001100";
            when 5 => sevenseg_out(13 downto 7) <= "0100100";
            when 6 => sevenseg_out(13 downto 7) <= "0100000";
            when 7 => sevenseg_out(13 downto 7) <= "0001111";
            when 8 => sevenseg_out(13 downto 7) <= "0000000";
            when 9 => sevenseg_out(13 downto 7) <= "0000100";
            when 10 => sevenseg_out(13 downto 7) <= "0001000";
            when 11 => sevenseg_out(13 downto 7) <= "1100000";
            when 12 => sevenseg_out(13 downto 7) <= "0110001";
            when 13 => sevenseg_out(13 downto 7) <= "1000010";
            when 14 => sevenseg_out(13 downto 7) <= "0100001";
            when 15 => sevenseg_out(13 downto 7) <= "0111001";
            when 16 => sevenseg_out(13 downto 7) <= "0010000";
            when 17 => sevenseg_out(13 downto 7) <= "0011110";
            when 18 => sevenseg_out(13 downto 7) <= "0001001";
            when 19 => sevenseg_out(13 downto 7) <= "0011000";
            when 20 => sevenseg_out(13 downto 7) <= "0000010";
            when 21 => sevenseg_out(13 downto 7) <= "0000001";
            when 22 => sevenseg_out(13 downto 7) <= "0000110";
            when 23 => sevenseg_out(13 downto 7) <= "0010000";
            when 24 => sevenseg_out(13 downto 7) <= "0001000";
            when 25 => sevenseg_out(13 downto 7) <= "0000010";
            when 26 => sevenseg_out(13 downto 7) <= "0010010";
            when 27 => sevenseg_out(13 downto 7) <= "0001100";
            when 28 => sevenseg_out(13 downto 7) <= "0110000";
            when 29 => sevenseg_out(13 downto 7) <= "0100010";
            when 30 => sevenseg_out(13 downto 7) <= "0110000";
            when 31 => sevenseg_out(13 downto 7) <= "0100000";
            when 32 => sevenseg_out(13 downto 7) <= "0011001";
            when 33 => sevenseg_out(13 downto 7) <= "0000011";
            when 34 => sevenseg_out(13 downto 7) <= "0000000";
            when 35 => sevenseg_out(13 downto 7) <= "0000101";
            when 36 => sevenseg_out(13 downto 7) <= "0001001";
            when 37 => sevenseg_out(13 downto 7) <= "1100001";
            when 38 => sevenseg_out(13 downto 7) <= "0110001";
            when 39 => sevenseg_out(13 downto 7) <= "0001101";
            when 40 => sevenseg_out(13 downto 7) <= "0000011";
            when 41 => sevenseg_out(13 downto 7) <= "0000100";
            when 42 => sevenseg_out(13 downto 7) <= "0010000";
            when 43 => sevenseg_out(13 downto 7) <= "0100111";
            when 44 => sevenseg_out(13 downto 7) <= "0010001";
            when 45 => sevenseg_out(13 downto 7) <= "0001000";
            when 46 => sevenseg_out(13 downto 7) <= "0100001";
            when 47 => sevenseg_out(13 downto 7) <= "0100101";
            when 48 => sevenseg_out(13 downto 7) <= "0000010";
            when 49 => sevenseg_out(13 downto 7) <= "0000011";
            when 50 => sevenseg_out(13 downto 7) <= "0000000";
            when 51 => sevenseg_out(13 downto 7) <= "0100110";
            when 52 => sevenseg_out(13 downto 7) <= "0111001";
            when 53 => sevenseg_out(13 downto 7) <= "0010010";
            when 54 => sevenseg_out(13 downto 7) <= "0000110";
            when 55 => sevenseg_out(13 downto 7) <= "0000010";
            when 56 => sevenseg_out(13 downto 7) <= "0010000";
            when 57 => sevenseg_out(13 downto 7) <= "0000100";
            when 58 => sevenseg_out(13 downto 7) <= "0000000";
            when 59 => sevenseg_out(13 downto 7) <= "0000010";
            when others => sevenseg_out(13 downto 7) <= "1111111";
        end case;

        case hours is
            when 0 => sevenseg_out(20 downto 14) <= "0000001";
            when 1 => sevenseg_out(20 downto 14) <= "1001111";
            when 2 => sevenseg_out(20 downto 14) <= "0010010";
            when 3 => sevenseg_out(20 downto 14) <= "0000110";
            when 4 => sevenseg_out(20 downto 14) <= "1001100";
            when 5 => sevenseg_out(20 downto 14) <= "0100100";
            when 6 => sevenseg_out(20 downto 14) <= "0100000";
            when 7 => sevenseg_out(20 downto 14) <= "0001111";
            when 8 => sevenseg_out(20 downto 14) <= "0000000";
            when 9 => sevenseg_out(20 downto 14) <= "0000100";
            when 10 => sevenseg_out(20 downto 14) <= "0001000";
            when 11 => sevenseg_out(20 downto 14) <= "1100000";
            when 12 => sevenseg_out(20 downto 14) <= "0110001";
            when 13 => sevenseg_out(20 downto 14) <= "1000010";
            when 14 => sevenseg_out(20 downto 14) <= "0100001";
            when 15 => sevenseg_out(20 downto 14) <= "0111001";
            when 16 => sevenseg_out(20 downto 14) <= "0010000";
            when 17 => sevenseg_out(20 downto 14) <= "0011110";
            when 18 => sevenseg_out(20 downto 14) <= "0001001";
            when 19 => sevenseg_out(20 downto 14) <= "0011000";
            when 20 => sevenseg_out(20 downto 14) <= "0000010";
            when 21 => sevenseg_out(20 downto 14) <= "0000001";
            when 22 => sevenseg_out(20 downto 14) <= "0000110";
            when 23 => sevenseg_out(20 downto 14) <= "0010000";
            when others => sevenseg_out(20 downto 14) <= "1111111";
        end case;

    end process;

end Behavioral;

该代码包含三个主要进程。第一个进程负责计算时间，并在每秒钟更新七段数码管显示。第二个进程负责在调整信号被触发时调整时间。第三个进程负责将当前时间转换为七段数码管的输入。

在FPGA板上实现该代码后，您可以使用adjust输入信号在需要时调整当前时间。