用 vhdl 语言设计 8 位数码扫描显示电路增加 8 个 4 位锁存器作为输出显示数据缓冲器，由外部输入8个待显示的十六进制数。

entity scan_display is
port(
clk: in std_logic;
reset: in std_logic;
data_in: in std_logic_vector(7 downto 0);
enable: in std_logic;
anodes: out std_logic_vector(7 downto 0);
segments: out std_logic_vector(6 downto 0)
);
end entity;

architecture behavioral of scan_display is
signal counter: integer := 0;
signal buffer: std_logic_vector(31 downto 0) := (others => '0');
signal data_out: std_logic_vector(31 downto 0) := (others => '0');

component bcd_decoder is
port(
bcd_in: in std_logic_vector(3 downto 0);
segment_out: out std_logic_vector(6 downto 0)
);
end component;

begin
-- Instantiate 4-bit BCD decoder
bcd: bcd_decoder port map(data_out(counter+3 downto counter), segments);

process(clk, reset)
begin
if reset = '1' then
counter <= 0;
buffer <= (others => '0');
data_out <= (others => '0');
elsif rising_edge(clk) then
if enable = '1' then
-- Store input data in buffer
buffer(counter+3 downto counter) <= data_in;

-- Update data_out with buffer values
data_out <= buffer;

-- Increment counter for next iteration
counter <= counter + 4;
if counter >= 32 then
counter <= 0;
end if;
end if;
end if;
end process;

-- Multiplex the 7-segment displays
anodes <= "11111110" when counter = 0 else
"11111101" when counter = 4 else
"11111011" when counter = 8 else
"11110111" when counter = 12 else
"11101111" when counter = 16 else
"11011111" when counter = 20 else
"10111111" when counter = 24 else
"01111111";

end behavioral;