使用状态机编写Binary-to-Gray代码（VHDL）

以下是使用状态机编写的Binary-to-Gray代码（VHDL）：

library ieee;
use ieee.std_logic_1164.all;

entity binary_to_gray is
    port (
        binary_in : in std_logic_vector(3 downto 0);
        gray_out : out std_logic_vector(3 downto 0)
    );
end binary_to_gray;

architecture Behavioral of binary_to_gray is
    type state_type is (s0, s1, s2, s3);
    signal current_state, next_state : state_type;
begin
    process(current_state, binary_in)
    begin
        case current_state is
            when s0 =>
                gray_out <= binary_in;
                next_state <= s1;
            when s1 =>
                gray_out <= binary_in xor (binary_in(1) & binary_in(0) & binary_in(3));
                next_state <= s2;
            when s2 =>
                gray_out <= binary_in xor (binary_in(2) & binary_in(1) & binary_in(0));
                next_state <= s3;
            when s3 =>
                gray_out <= binary_in xor (binary_in(3) & binary_in(2) & binary_in(1));
                next_state <= s0;
        end case;
    end process;

    process(current_state)
    begin
        case current_state is
            when s0 =>
                current_state <= s1;
            when s1 =>
                current_state <= s2;
            when s2 =>
                current_state <= s3;
            when s3 =>
                current_state <= s0;
        end case;
    end process;

    next_state <= s0 when current_state = s3 else next_state;

    process(current_state, next_state)
    begin
        if current_state /= next_state then
            current_state <= next_state;
        end if;
    end process;
end Behavioral;

这个代码使用了一个状态机来实现Binary-to-Gray的转换。在每个时钟周期中，状态机会根据当前状态和输入的Binary值计算出输出的Gray值，并将状态更新为下一个状态。最终的Gray值将在下一个时钟周期中输出。