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检测一段序列这里给出两种方法讨论：1.状态机；2.移位寄存器。例子：检测序列1011。

第一种方法：状态机。（这里采用一段式状态机）话不多说，上代码。

module fsm(
	input clk,
	input rst_n,
	input din,
    output reg led                    
);
reg [2:0] state;
localparam s_idle = 4'b0001,s_1 = 4'b0010,s_10 = 4'b0100,s_101 = 4'b1000;

always@(posedge clk or negedge rst_n)
	if(!rst_n)begin
		state <= s_idle;
		led <= 1'b1;
		end
	else begin
		case(state)
			s_idle : 
				if(din == "1")
					state <= s_1;
				else state <= s_idle;
			s_1 :
				if(din == "0")
					state <= s_10;
				else state <= s_1;
			s_10 :
				if(din == "1")
					state <= s_101;
				else state <= s_10;
			s_101 : 
				if(din == "1")begin
					state <= s_idle;
					led <= ~led;
					end
				else 
				led <= led;
		default : state <= s_idle;
		endcase
	end
endmodule
	
	
	

第二种方法：移位寄存器。代码如下：

module xulie(
	input clk,
	input rst_n,
	input din,
	output reg match

);
reg [2:0] match_d;
always@(posedge clk or negedge rst_n)
	if(!rst_n)
		match_d <= 3'd0;
	else
		match_d <= {match_d[1:0] , din};

always@(posedge clk or negedge rst_n)
	if(!rst_n)
		match <= 1'b0;
	else if(din && (match_d == 3'b101))
		match <= 1'b1;
	else if(match)
		match <= 1'b0;
endmodule

仿真如图：在检测到1011序列后，match输出一高电平。