题解 | Johnson Counter

`timescale 1ns/1ns

module JC_counter(
   input                clk ,
   input                rst_n,
 
   output reg [3:0]     Q  
);
// 法1
/*
reg [2:0] cnt;
always@(posedge clk or negedge rst_n)begin
    if(!rst_n)begin
        cnt <= 'd0;
    end 
    else begin
        cnt <= cnt + 1;
    end 
end

always@(*)begin
    case(cnt)
    3'b000: Q = 4'b0000;
    3'b001: Q = 4'b1000;
    3'b010: Q = 4'b1100;
    3'b011: Q = 4'b1110;
    3'b100: Q = 4'b1111;
    3'b101: Q = 4'b0111;
    3'b110: Q = 4'b0011;
    3'b111: Q = 4'b0001;

    endcase
end
*/
// 法2
always@(posedge clk or negedge rst_n)begin
    if(!rst_n)begin
        Q  <= 4'b0000;
    end
    else begin
        Q <= {~Q[0],Q[3:1]};
    end
end

endmodule