从计数器到可控线性序列机——LED灯实验六部曲

一、代码实现

设计定义：让LED灯按照亮0.25s,灭0.5s,亮0.75s，灭1s的状态循环。

`timescale 1ns / 1ps

module led_step2(
    input   clk  ,
    input   rstn ,
    output  led  
);
    reg[26:0]     cnt   ;
    reg           r_led ;
    assign  led = r_led ;

parameter  MCNT = 125_000_000;

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

always @(posedge clk or negedge rstn) begin
    if(!rstn)
        r_led <= 1;
    else if(cnt == MCNT/10 - 1)
        r_led <= 0;
    else if(cnt == MCNT *3/10 - 1)
        r_led <= 1;
    else if(cnt == MCNT *3/5 - 1)
        r_led <= 0;
    else if(cnt == MCNT - 1)
        r_led <= 1;
    else
        r_led <= r_led;
    
end
endmodule

二、仿真

`timescale 1ns / 1ns

module led_step1_tb();

    reg    clk  ;
    reg    rstn ;
    wire   led  ;

led_step2 #(
    .MCNT(125_000)
)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