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我做了一个计数器，在两个信号的控制下启动和停止计数
并且在计数完成后，输出一个脉冲信号，如果clk直接接外部50M晶振的话，输出没有问题，但如果接PLL的话（甚至倍频到80M），计数完成后输出的脉冲就直接输出杂声（高频），请高手指教一二.....，谢谢！

module counter(clk_in,start,stop,rst,count_num,count_over);
input clk_in,start,stop,rst;
output[7:0] count_num;

output count_over;
reg count_over;

reg [7:0] count_num;
reg [32:0] count_over_wide;
reg [32:0] count_out_wide;

parameter pulsewide=80;
reg count_flag;
reg count_over_flag;

always@(negedge start or posedge stop or negedge rst)
 begin
  if(!rst)
   count_flag<=0;
  else if(stop)
   begin
   count_flag<=0;
   end
  else  count_flag<=1;
 end

always@(posedge clk_in )
begin
 if(!rst)
  begin

   count_num<=0;

  end
    else if(count_flag==1)
  begin
   count_num<=count_num+1;
   end  
   

end

 always@(posedge clk_in)
  begin
   if(!rst)
    begin
     count_over_flag<=0;
     count_over_wide<=0;
     count_over<=0;
    end
   else if((stop)&(!count_over_flag))
     count_over_flag<=1;

   else if(count_over_flag==1)
    begin
     if(count_over_wide<=pulsewide)
      begin
       count_over<=1;
       count_over_wide<=count_over_wide+1;
      end
     else
      begin
       count_over_flag<=0;
       count_over_wide<=0;
      end
    end
   else
    count_over<=0;
  end

endmodule