Traffic light controller FSM in Verilog - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the state register.

Verilog

reg [1:0] [1]; // 2-bit state register

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Astate

Btimer

Ccounter

Dflag

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated names like counter or timer for the state register.

The state register is usually named state to hold the current FSM state.

2fill in blank

medium

Complete the code to define the state encoding for RED.

Verilog

localparam RED = 2'b[1];

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A11

B01

C10

D00

Attempts:

3 left

💡 Hint

Common Mistakes

Using 01 or 10 which represent other states.

The RED state is encoded as 2'b00 in this FSM.

3fill in blank

hard

Fix the error in the always block sensitivity list.

Verilog

always @([1]) begin
  if (reset) state <= RED;
  else state <= next_state;
end

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Areset

Bposedge clk

Cposedge clk or posedge reset

Dnegedge reset

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting reset or using wrong edge triggers.

The sensitivity list must include the clock and asynchronous reset signals with posedge.

4fill in blank

hard

Fill both blanks to complete the next state logic for RED to GREEN transition.

Verilog

always @(*) begin
  case(state)
    RED: if(timer [1] RED_TIME) next_state = [2]; else next_state = RED;
    default: next_state = RED;
  endcase
end

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A>=

B<

CGREEN

DYELLOW

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than instead of greater or equal.

Setting next state incorrectly to YELLOW.

The FSM moves from RED to GREEN when the timer reaches or exceeds RED_TIME.

5fill in blank

hard

Fill all three blanks to complete the output logic for traffic lights.

Verilog

always @(*) begin
  case(state)
    RED: begin
      red_light = [1];
      yellow_light = [2];
      green_light = [3];
    end
    // other states omitted
  endcase
end

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A1'b1

B1'b0

Attempts:

3 left

💡 Hint

Common Mistakes

Turning on yellow or green lights in RED state.

In RED state, red_light is ON (1), yellow_light and green_light are OFF (0).