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The priority encoder overcome the drawback of binary encoder that generates invalid output for more than one input line is set to high. The priority encoder prioritizes each input line and provides an encoder output corresponding to its highest input priority.

The priority encoder is widely used in digital applications. One common example of a microprocessor detecting the highest priority interrupt. The priority encoders are also used in navigation systems, robotics for controlling arm positions, communication systems, etc.

8:3 Priority Encoder

Block Diagram

priority encoder

Truth Table

priority encoder truth table

8:3 Priority Encoder Verilog Code

module priority_encoder(
  input [7:0] D,
  output reg [2:0] y);
  
  always@(D) begin
    casex(D)
      8'b1xxx_xxxx: y = 3'b111;
      8'b01xx_xxxx: y = 3'b110;
      8'b001x_xxxx: y = 3'b101;
      8'b0001_xxxx: y = 3'b100;
      8'b0000_1xxx: y = 3'b011;
      8'b0000_01xx: y = 3'b010;
      8'b0000_001x: y = 3'b001;
      8'b0000_0001: y = 3'b000;
      default: $display("Invalid data received");
    endcase
  end
endmodule

Testbench Code

module tb;
  reg [7:0] D;
  wire [2:0] y;
  
  priority_encoder pri_enc(D, y);
  
  initial begin
    $monitor("D = %b -> y = %0b", D, y);
    repeat(5) begin
      D=$random; #1;
    end
  end
endmodule

Output:

D = 00100100 -> y = 101
D = 10000001 -> y = 111
D = 00001001 -> y = 11
D = 01100011 -> y = 110
D = 00001101 -> y = 11

Verilog Codes