利用FPGA输出占空比可调的方波

一开始我不太认同通过测试文件的输入值改变占空比的做法符合要求，总感觉这等同于多次不同的测试放到了一起。后来感觉手动调占空比也符合要求，可以对应开发板上一个按键，来改变占空比。

手动调的方案

module PWM(clk,rst_n,duty,PWM_wave);
	input clk;
	input [6:0] duty;
	input rst_n;
	output reg PWM_wave;

	reg [7:0] count;
	
	[e-mail](posedge clk or negedge rst_n)
		begin
			if(!rst_n)
				begin
				PWM_wave<=0;
				count<=8'd0;
				end
			else
				begin
				if(count>=8'd100)
					count<=8'd0;
				if(count<8'd100)
					count<=count+8'd1;
					
				if(count<duty)
					PWM_wave<=1;
				if(count>=duty)
					PWM_wave<=0;
				end
		end

endmodule

测试文件

`timescale 10ns/1ns
module test();

	reg clk;
	reg rst_n;
	reg [6:0] duty;
	wire PWM_wave;
	
	PWM u1(.clk(clk),.rst_n(rst_n),.duty(duty),.PWM_wave(PWM_wave));
	
	initial 
		begin
	     clk<=0;
		 rst_n=0;
		 duty=7'd10;
		 #10 rst_n=1;
		 #100	duty=7'd30;
		 #100	duty=7'd50;
		 #100	duty=7'd70;
		 end
		 
	always #10 clk<=~clk;
	
endmodule

自动改变占空比的程序可对应呼吸灯实例，代码如下

顶层文件

module top_pwm(CLK_50M,RST_N,pwm_out);

	input CLK_50M;
	input RST_N;
	output  pwm_out;
	wire 	CLK_1M;
	
	fenpin i1(.CLK_50M(CLK_50M),.RST_N(RST_N),.CLK_1M(CLK_1M));
	PWM    i2(.CLK_1M(CLK_1M),.RST_N(RST_N),.pwm_out(pwm_out));
	
endmodule

PWM程序

module PWM(CLK_1M,RST_N,pwm_out);

	input CLK_1M;
	input RST_N;
	output  pwm_out;
		
	reg [6:0]  time_cnt;
	reg [6:0]  turn_reg;
	reg  pwm_reg;
	reg  flag;
//---------------------------------------------
	parameter   period=7'd50;
	parameter   turn=7'd30;
//---------------------------------------------------

	always  @ (posedge CLK_1M or negedge RST_N)
		begin
			if(!RST_N)
				begin
				time_cnt <= 7'd0;
				pwm_reg<= 1'b0;
				turn_reg<=turn;
				end
			else
				begin
				time_cnt<=time_cnt+7'd1;
				
				if(turn_reg==turn)
					flag=1'b0;
				if(turn_reg==7'd1)
					flag=1'b1;
				if ( time_cnt <= turn_reg-1) 
					pwm_reg <= 1'b0;
				if (( time_cnt > turn_reg-1) && (time_cnt<period-1))
					pwm_reg <= 1'b1;
					
				if(time_cnt==period-1)
					begin
					time_cnt <= 7'd0;
					if(flag==1'b1)
						turn_reg<=turn_reg+7'd1;	
					if(flag==1'b0)
						turn_reg<=turn_reg-7'd1;
					end
				end
		end
 
   assign  pwm_out= pwm_reg;
	
 endmodule

分频产生1MHz时钟

module fenpin(CLK_50M,RST_N,CLK_1M);

	input CLK_50M ;
	input RST_N;
	output CLK_1M;
	
	reg [6:0] time_cnt;
	reg  CLK_1M;
	parameter period=7'd25;
	
	[e-mail](posedge CLK_50M or negedge RST_N)
		begin
			if(!RST_N)
				begin
				time_cnt<=7'd0;
				CLK_1M<=1'b0;
				end
			else
				begin
				time_cnt<=time_cnt+7'd1;
				if(time_cnt==period-1)
					begin
					CLK_1M<=~CLK_1M;
					time_cnt<=7'd0;
					end
				end
		end
endmodule
	

测试文件

`timescale 1ns/1ns

module pwm_test();
	
	reg CLK_50M;
	reg RST_N;
	wire pwm_out;
	
	top_pwm  u1 (.CLK_50M(CLK_50M),.RST_N(RST_N),.pwm_out(pwm_out));
	
	initial 
		begin
		
		RST_N=0;
		CLK_50M=0;
		#10 RST_N=1;
		#10 RST_N=0;
		#10 RST_N=1;
		end
		
	always  #10 CLK_50M=~CLK_50M;
	
endmodule

仿真波形