//========================================== 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 rr