从计数器到可控线性序列机——LED灯实验六部曲

设计定义：1.让LED灯按照亮0.25s，灭0.75的状态循环亮灭

一、代码实现 

`timescale 1ns / 1ns

module led_step1(
    input   clk  ,
    input   rstn ,
    output  led  
    );

    reg[23:0]    cnt   ;
    reg[1:0]     count ;
    reg          r_led ;
    assign led = r_led ;

always @(posedge clk or negedge rstn) begin
    if(!rstn)
        cnt <= 0;
    else if(cnt == 12_500_000  - 1)
        cnt <= 0;
    else
        cnt <= cnt + 1'd1;
end

always @(posedge clk or negedge rstn) begin
    if(!rstn)
        count <= 0;
    else if(cnt == 12_500_000  - 1)
        count <= count + 1'd1;
end

always @(*) begin
    case(count)
    2'b00: r_led <= 1;
    2'b01: r_led <= 0;
    2'b10: r_led <= 0;
    2'b11: r_led <= 0;
    default: r_led <= 0;
    endcase
end

endmodule

 

二、仿真 

`timescale 1ns / 1ns

module led_step1_tb();

    reg    clk  ;
    reg    rstn ;
    wire   led  ;

led_step1 inst0(
    .clk  (clk ) ,
    .rstn (rstn) ,
    .led  (led ) 
    );

initial  clk = 1;
always #10 clk = ~clk;

initial begin
    rstn = 0;
    #201;
    rstn = 1;
    #1000_000_000;
    $stop;
end
endmodule