====呼吸灯设计文件====

<code verilog>
// --------------------------------------------------------------------
// >>>>>>>>>>>>>>>>>>>>>>>>> COPYRIGHT NOTICE <<<<<<<<<<<<<<<<<<<<<<<<<
// --------------------------------------------------------------------
// Module: Breath_led
// 
// Author: Step
// 
// Description: PWM-Breath_led
// 
// Web: www.ecbcamp.com
//
// --------------------------------------------------------------------
// Code Revision History :
// --------------------------------------------------------------------
// Version: |Mod. Date:   |Changes Made:
// V1.0     |2015/11/11   |Initial ver
// --------------------------------------------------------------------
module Breath_led #
(
parameter	CNT_NUM = 5000	//period = (5000^2)*2 = 50000000 = 2s
)
(
input		clk_in,			//system clk
input		rst_n_in,			//system reset
output		Breath_led		//Breath led output
);

reg	[12:0]	cnt1;
//generate cnt1 signal
always@(posedge clk_in or negedge rst_n_in) begin 
	if(!rst_n_in) begin
		cnt1<=13'd0;
	end else begin
		if(cnt1>=CNT_NUM-1) cnt1<=1'b0;
		else cnt1<=cnt1+1'b1;
	end
end

reg	flag;
reg	[12:0]	cnt2;
//generate cnt2 signal
always@(posedge clk_in or negedge rst_n_in) begin 
	if(!rst_n_in) begin
		cnt2<=13'd0;
		flag<=1'b0;
	end else begin
		if(cnt1==CNT_NUM-1) begin
			if(!flag) begin
				if(cnt2>=CNT_NUM-1) flag<=1'b1;
				else cnt2<=cnt2+1'b1;
			end else begin
				if(cnt2<=0) flag<=1'b0;
				else cnt2<=cnt2-1'b1;
			end
		end else cnt2<=cnt2;
	end
end

//Compare cnt1 and cnt2, generate PWM-Breath-led
assign	Breath_led = (cnt1<cnt2)?1'b0:1'b1;
	
endmodule
	
</code>