module led_test (
clk, // 开发板上输入时钟: 50Mhz
rst_n, // 开发板上输入复位按键
led // 输出LED灯,用于控制开发板上四个LED(LED1~LED4)
);
input clk;
input rst_n;
output [3:0] led;
//寄存器定义
reg [31:0] timer;
reg [3:0] led;
//===========================================================================
// 计数器计数:循环计数0~4秒//为了将四个灯持续显示4秒
//===========================================================================
always @(posedge clk or negedge rst_n) //检测时钟的上升沿和复位的下降沿
begin
if (~rst_n) //复位信号低有效
timer <= 0; //计数器清零
else if (timer == 32'd199_999_999) //开发板使用的晶振为50MHz，4秒计数(50M*4-1=199_999_999)
timer <= 0; //计数器计到4秒，计数器清零
else
timer <= timer 1'b1; //计数器加1
End
always @(posedge clk or negedge rst_n) //检测时钟的上升沿和复位的下降沿
begin
if (~rst_n) //复位信号低有效
led <= 4'b1111; //LED灯输出全为高，四个LED灯亮
else if (timer == 32'd49_999_999) //计数器计到1秒，
led <= 4'b1110; //LED1点灭
else if (timer == 32'd99_999_999) //计数器计到2秒，
led <= 4'b1101; //LED2点灭
else if (timer == 32'd149_999_999) //计数器计到3秒，
led <= 4'b1011; //LED3点灭
else if (timer == 32'd199_999_999) //计数器计到4秒，
led <= 4'b0111; //LED4点灭
End
Endmodule
用户约束文件
代码语言：js复制
NET clk LOC = T8 | TNM_NET = sys_clk_pin | IOSTANDARD = "LVCMOS33";//明明时钟网络
TIMESPEC TS_sys_clk_pin = PERIOD sys_clk_pin 50000 kHz;//设置时间精度，配置时钟
NET rst_n LOC = L3 | IOSTANDARD = "LVCMOS33";
NET led<0> LOC = P4 | IOSTANDARD = "LVCMOS33";
NET led<1> LOC = N5 | IOSTANDARD = "LVCMOS33";
NET led<2> LOC = P5 | IOSTANDARD = "LVCMOS33";
NET led<3> LOC = M6 | IOSTANDARD = "LVCMOS33";
