Sequence Detector 1010 (Moore Machine + Mealy Machine + Overlapping/Non-Overlapping)

Yue Guo

Hi, this post is about how to design and implement a sequence detector to detect 1010. This is the fifth post of the series. The previous posts can be found here: sequence 1011, sequence 1001, sequence 101, and sequence 110. I am going to cover both the Moore machine and Mealy machine in overlapping and non-overlapping cases.

1) Moore Machine (Non-Overlapping)

module sd1010_moore(input bit clk,
                   input logic reset,
                   input logic din,
                   output logic dout);

  typedef enum logic [2:0] {S0, S1, S2, S3, S4} state_t;
  state_t state;

  always @(posedge clk or posedge reset) begin
    if(reset) begin
      dout <= 1'b0;
      state <= S0;
    end
    else begin
      case(state)
        S0: begin
          dout <=1'b0;
          if(din)
            state <= S1;
        end
        S1: begin
          dout <= 1'b0;
          if(~din)
            state <= S2;
        end
        S2: begin
          dout <= 1'b0;
          if(din)
            state <= S3;
          else
            state <= S0;
        end
        S3: begin
          dout <= 1'b0;
          if(din)
            state <= S1;
          else
            state <= S4;
        end
        S4: begin
          dout <= 1'b1;
          if(din)
            state <= S1;
          else
            state <= S0;
        end
      endcase
    end
  end


endmodule

2) Mealy Machine (Non-Overlapping)

module sd1010_mealy(input bit clk,
                   input logic reset,
                   input logic din,
                   output logic dout);

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

  always @(posedge clk or posedge reset) begin
    if(reset) begin
      dout <= 1'b0;
      state <= S0;
    end
    else begin
      case(state)
        S0: begin
          if(din) begin
            state <= S1;
            dout <=1'b0;
          end
          else
            dout <=1'b0;
        end
        S1: begin
          if(~din) begin
            state <= S2;
            dout <=1'b0;
          end
          else begin
            dout <=1'b0;
          end
        end
        S2: begin
          if(~din) begin
            state <= S0;
            dout <=1'b0;
          end
          else begin
            state <= S3;
            dout <=1'b0;
          end
        end
        S3: begin
          if(din) begin
            state <= S1;
            dout <=1'b0;
          end
          else begin
            state <= S0;
            dout <=1'b1;
          end
        end
      endcase
    end
  end

endmodule

3) Moore Machine (Overlapping)

module sd1010_moore_over(input bit clk,
                   input logic reset,
                   input logic din,
                   output logic dout);

  typedef enum logic [2:0] {S0, S1, S2, S3, S4} state_t;
  state_t state;

  always @(posedge clk or posedge reset) begin
    if(reset) begin
      dout <= 1'b0;
      state <= S0;
    end
    else begin
      case(state)
        S0: begin
          dout <=1'b0;
          if(din)
            state <= S1;
        end
        S1: begin
          dout <= 1'b0;
          if(~din)
            state <= S2;
        end
        S2: begin
          dout <= 1'b0;
          if(din)
            state <= S3;
          else
            state <= S0;
        end
        S3: begin
          dout <= 1'b0;
          if(din)
            state <= S1;
          else
            state <= S4;
        end
        S4: begin
          dout <= 1'b1;
          if(din)
            state <= S3;
          else
            state <= S0;
        end
      endcase
    end
  end


endmodule

4) Mealy Machine (Overlapping)

module sd1010_mealy_over(input bit clk,
                   input logic reset,
                   input logic din,
                   output logic dout);

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

  always @(posedge clk or posedge reset) begin
    if(reset) begin
      dout <= 1'b0;
      state <= S0;
    end
    else begin
      case(state)
        S0: begin
          if(din) begin
            state <= S1;
            dout <=1'b0;
          end
          else
            dout <=1'b0;
        end
        S1: begin
          if(~din) begin
            state <= S2;
            dout <=1'b0;
          end
          else begin
            dout <=1'b0;
          end
        end
        S2: begin
          if(~din) begin
            state <= S0;
            dout <=1'b0;
          end
          else begin
            state <= S3;
            dout <=1'b0;
          end
        end
        S3: begin
          if(din) begin
            state <= S1;
            dout <=1'b0;
          end
          else begin
            state <= S2;
            dout <=1'b1;
          end
        end
      endcase
    end
  end

endmodule

That’s all for sequence detectors 1010. Let me know if you have any questions or any thoughts.

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