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module led_flash(
                 clk,rst_n,
                 led
                 );
                 
    input clk;          //50MHz
    input rst_n;        //复位信号，低电平有效
    
    output reg[7: 0] led;   //8个LED灯
    
    reg[23: 0] cnt;     //计数器，最大可以计到2^24 *20 ns ,大约320ms
    
    always @(posedge clk or negedge rst_n)
        if(!rst_n)
            cnt <= 24'b0;
        else
            cnt <= cnt + 1'b1;     //循环计数
            
    //reg[7: 0] led_r;
       
    always @(posedge clk or negedge rst_n)
        if(!rst_n)
            led <= 8'b11111111;
        else 
        begin
        if(cnt == 24'hffffff)   //每大约320ms led_r进行翻转
            led <= ~led;
        else led <= led; 
    //assign led = led_r;    
    end

endmodule