FPGA入门实验-呼吸灯实现

任务目标

实现呼吸灯效果。

实现代码

`timescale 1ns / 1ps

module breathled(
    input sysclk    ,
    input rst_n     ,
    output led
    );
    reg [31:0] cnt_ms;
    reg [31:0] cnt_us;
    reg [31:0] cnt_ns;
    reg cnt_s;
    always@(posedge sysclk)
        if(!rst_n)begin
            cnt_ms <= 32'd0;
            cnt_us <= 32'd0;
            cnt_ns <= 32'd0;
            cnt_s  <= 32'd0;   
        end
        else if(cnt_ms >= 999 && cnt_us >= 999 && cnt_ns >= 124)begin
            cnt_ms <= 32'd0;
            cnt_us <= 32'd0;
            cnt_ns <= 32'd0;
            cnt_s  <= cnt_s + 32'd1;
        end
        else if(cnt_us >= 999 && cnt_ns >= 124)begin
            cnt_ms <= cnt_ms + 32'd1;
            cnt_us <= 32'd0;
            cnt_ns <= 32'd0;
            cnt_s  <= cnt_s;
        end
        else if(cnt_ns >= 124)begin
            cnt_ms <= cnt_ms;
            cnt_us <= cnt_us + 32'd1;
            cnt_ns <= 32'd0;
            cnt_s  <= cnt_s;
        end
        else begin
            cnt_ms <= cnt_ms;
            cnt_us <= cnt_us;
            cnt_ns <= cnt_ns + 32'd1;
            cnt_s  <= cnt_s;    
        end
    assign led = (!cnt_s) ? ((cnt_ms >= cnt_us) ? 1:0) : ((cnt_ms >= cnt_us) ? 0:1);
endmodule

结语

呼吸灯最根本的原理也就是PWM占空比的变化，导致LED单位时间实际平均电压变化。