vhdl和verilog的状态机怎么写

VHDL状态机的写法：

首先，需要定义状态机的状态，可以使用枚举类型。例如：

type state_type is (S0, S1, S2, S3);

然后，需要定义状态机的输入和输出信号。例如：

signal input_signal : std_logic;
signal output_signal : std_logic;

接下来，可以使用process语句来实现状态机的行为。在process语句中，使用case语句来根据当前状态和输入信号确定下一状态和输出信号。例如：

process (input_signal, current_state)
begin
    case current_state is
        when S0 =>
            if input_signal = '1' then
                next_state <= S1;
                output_signal <= '0';
            else
                next_state <= S0;
                output_signal <= '0';
            end if;
        when S1 =>
            if input_signal = '1' then
                next_state <= S2;
                output_signal <= '1';
            else
                next_state <= S0;
                output_signal <= '0';
            end if;
        when S2 =>
            if input_signal = '1' then
                next_state <= S3;
                output_signal <= '0';
            else
                next_state <= S0;
                output_signal <= '0';
            end if;
        when S3 =>
            if input_signal = '1' then
                next_state <= S0;
                output_signal <= '1';
            else
                next_state <= S0;
                output_signal <= '0';
            end if;
    end case;
end process;

Verilog状态机的写法：

与VHDL类似，需要定义状态机的状态、输入和输出信号。例如：

typedef enum logic [1:0] {S0, S1, S2, S3} state_type;

logic input_signal;
logic output_signal;
state_type current_state, next_state;

然后，可以使用always块来实现状态机的行为。在always块中，使用case语句来根据当前状态和输入信号确定下一状态和输出信号。例如：

always @(input_signal or current_state)
begin
    case (current_state)
        S0:
            begin
                if (input_signal) begin
                    next_state = S1;
                    output_signal = 1'b0;
                end
                else begin
                    next_state = S0;
                    output_signal = 1'b0;
                end
            end
        S1:
            begin
                if (input_signal) begin
                    next_state = S2;
                    output_signal = 1'b1;
                end
                else begin
                    next_state = S0;
                    output_signal = 1'b0;
                end
            end
        S2:
            begin
                if (input_signal) begin
                    next_state = S3;
                    output_signal = 1'b0;
                end
                else begin
                    next_state = S0;
                    output_signal = 1'b0;
                end
            end
        S3:
            begin
                if (input_signal) begin
                    next_state = S0;
                    output_signal = 1'b1;
                end
                else begin
                    next_state = S0;
                    output_signal = 1'b0;
                end
            end
    endcase
end