reg[0:3] 与reg[3:0] 流水灯

reg [0:3] led 当定义 led <= 4’b0001; 则复位的时候最右侧的灯先亮

reg [3:0] led 当定义 led <= 4’b0001; 则复位的时候最左侧的灯先亮

module flow_led(
    input               sys_clk  ,  //系统时钟
    input               sys_rst_n,  //系统复位，低电平有效
     
    output  reg  [0:3]  led         //4个LED灯
    );

//reg define
reg [23:0] counter;

//*****************************************************
//**                    main code
//***************************************************** 
                                                                                                                                                                                                                         
//计数器对系统时钟计数，计时0.2秒
always @(posedge sys_clk or negedge sys_rst_n) begin
    if (!sys_rst_n)
        counter <= 24'd0;
    else if (counter < 24'd1000_0000)
        counter <= counter + 1'b1;
    else
        counter <= 24'd0;
end

//通过移位寄存器控制IO口的高低电平，从而改变LED的显示状态
always @(posedge sys_clk or negedge sys_rst_n) begin
    if (!sys_rst_n)
        led <= 4'b0001;
    else if(counter == 24'd1000_0000) 
        led[0:3] <= {led[3],led[0:2]};
    else
        led <= led;
end

endmodule