1.用verilog实现PWM控制呼吸灯。呼吸周期2秒:1秒逐渐变亮,1秒逐渐变暗。系统时钟24MHz,pwm周期1ms,精度1us。
====
```verilog
`timescale 1ns/1ps
module pwm(
input Sys_clk,//24Mhz, 42ns
input Sys_reset,
output Pwm_o//T=1ms/1us
);
parameter T1ns = 5'd24;
parameter T1000us = 10'd1000;
reg [9:0] cnt_us;
reg [4:0] cnt_ns;
reg iscount;
//****************************************
always @ (posedge Sys_clk or negedge Sys_reset)
if(!Sys_reset)
cnt_ns <= 5'd0;
else if(iscount & cnt_ns == T1ns)
cnt_ns <= 5'd0;
else if(!iscount) cnt_ns <= 5'd0;
else
cnt_ns<= cnt_ns+1'b1;
//******************************************
always @ (posedge Sys_clk , negedge Sys_reset)
&n