Craft a sequence detector to identify the pattern 101 in a serial bit stream.

Question

Anonymous · Accepted Answer

module sequence_detector(
    input clk,
    input reset,
    input bit_in,
    output reg sequence_detected
);

// Define the states
    typedef enum logic [1:0] {
        S0, // Initial state
        S1, // Detected '1'
        S2, // Detected '10'
        S3  // Detected '101'
    } state_t;

state_t current_state, next_state;

// State transition
    always @(posedge clk or posedge reset) begin
        if (reset)
            current_state <= S0;
        else
            current_state <= next_state;
    end

// Next state logic
    always @(*) begin
        case (current_state)
            S0: begin
                if (bit_in == 1)
                    next_state = S1;
                else
                    next_state = S0;
            end
            S1: begin
                if (bit_in == 0)
                    next_state = S2;
                else
                    next_state = S1;
            end
            S2: begin
                if (bit_in == 1)
                    next_state = S3;
                else
                    next_state = S0;
            end
            S3: begin
                if (bit_in == 1)
                    next_state = S1;
                else
                    next_state = S0;
            end
            default: next_state = S0;
        endcase
    end

// Output logic
    always @(posedge clk or posedge reset) begin
        if (reset)
            sequence_detected <= 0;
        else if (current_state == S3)
            sequence_detected <= 1;
        else
            sequence_detected <= 0;
    end

endmodule

Anonymous · Answer

To solve this detector, essentially you would need a finite state machine. first
you need to draw the state diagram of the transition while detecting the
sequence. Then in verilog, you need to implement the case statement.

Craft a sequence detector to identify the pattern 101 in a serial bit stream.

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