src/edu/berkeley/fleet/fpga/mem/gray_counter.v

   1 //==========================================
   2 // Function : Code Gray counter.
   3 // Coder    : Alex Claros F.
   4 // Date     : 15/May/2005.
   5 //=======================================
   6
   7 `timescale 1ns/1ps
   8
   9 module GrayCounter
  10    #(parameter   COUNTER_WIDTH = 2)
  11
  12     (output reg  [COUNTER_WIDTH-1:0]    GrayCount_out,  //'Gray' code count output.
  13
  14      input wire                         Enable_in,  //Count enable.
  15      input wire                         Clear_in,   //Count reset.
  16
  17      input wire                         Clk);
  18
  19     /////////Internal connections & variables///////
  20     reg    [COUNTER_WIDTH-1:0]         BinaryCount;
  21
  22     /////////Code///////////////////////
  23
  24     always @ (posedge Clk)
  25         if (Clear_in) begin
  26             BinaryCount   <= {COUNTER_WIDTH{1'b 0}} + 1;  //Gray count begins @ '1' with
  27             GrayCount_out <= {COUNTER_WIDTH{1'b 0}};      // first 'Enable_in'.
  28         end
  29         else if (Enable_in) begin
  30             BinaryCount   <= BinaryCount + 1;
  31             GrayCount_out <= {BinaryCount[COUNTER_WIDTH-1],
  32                               BinaryCount[COUNTER_WIDTH-2:0] ^ BinaryCount[COUNTER_WIDTH-1:1]};
  33         end
  34
  35 endmodule