流水灯

// hled.v
/**************************************************************
**  模块名称：LED
**  功能描述：流水灯
**************************************************************/
module LED(
                                    clk48M,                                        //48M 时钟输入
                                    RSTn,                                          //复位信号，高电平复
                                    LED                                            //LED 输出
                      );
input                          clk48M;                                  
input                          RSTn;   
output    [3:0]            LED;              
//reg      [3:0]              LED;                 
reg      [23:0]          count;              //分频计数器 
reg      [3:0]          ld;

clk48M or negedge RSTn)                                                                        
begin
        if(!RSTn)                                                                  //异步复位
        begin
                ld<=4'h8;                                                      //复位后，LED 高位点亮            
                count<=24'h0;              //计数器赋初值
        end
        else
        begin
                count<=count+1;                                                                        
                if(count==24'hff_ff_ff)                                        
                begin
                                ld<=ld>>1;                                //LED 移位输出
                                count<=0;
                                if(ld==4'h0)          //LED 复位
                                        ld<=4'h8;                              
                end
          end
end
assign LED=~ld;             //用连续赋值
endmodule