文章目录
一、呼吸灯
呼吸灯是指灯光在微电脑的控制之下完成由亮到暗的逐渐变化，使用开发板上的四个led灯实现1s间隔的呼吸灯。
二、代码实现
c
```c
module pwm_led(
input clk ,
input rst_n ,
output reg [3:0] led
);
parameter CNT_US = 6'd49;//50x20=1000ns=1us
parameter CNT_MS = 10'd999;//1usx1000=1ms
parameter CNT_S = 10'd999;//1msx1000=1s
reg [5:0] cnt_us;
wire add_cnt_us;
wire end_cnt_us;
reg [9:0] cnt_ms;
wire add_cnt_ms;
wire end_cnt_ms;
reg [9:0] cnt_s;
wire add_cnt_s;
wire end_cnt_s;
reg flag;//闪烁标志
always @(posedge clk or negedge rst_n)begin
if(!rst_n)begin
cnt_us <= 0;
end
else if(add_cnt_us)begin
if(end_cnt_us)begin
cnt_us <= 0;
end
else begin
cnt_us <= cnt_us + 1;
end
end
else begin
cnt_us <= cnt_us;
end
end
assign add_cnt_us = 1'd1;
assign end_cnt_us = add_cnt_us && cnt_us == CNT_US;
always @(posedge clk or negedge rst_n)begin
if(!rst_n)begin
cnt_ms <= 0;
end
else if(add_cnt_ms)begin
if(end_cnt_ms)begin
cnt_ms <= 0;
end
else begin
cnt_ms <= cnt_ms + 1;
end
end
else begin
cnt_ms <= cnt_ms;
end
end
assign add_cnt_ms = end_cnt_us;
assign end_cnt_ms = add_cnt_ms && cnt_ms == CNT_MS;
always @(posedge clk or negedge rst_n)begin
if(!rst_n)begin
cnt_s <= 0;
end
else if(add_cnt_s)begin
if(end_cnt_s)begin
cnt_s <= 0;
end
else begin
cnt_s <= cnt_s + 1;
end
end
else begin
cnt_s <= cnt_s;
end
end
assign add_cnt_s = end_cnt_ms;
assign end_cnt_s = add_cnt_s && cnt_s == CNT_S;
always @(posedge clk or negedge rst_n)begin
if(!rst_n)begin
flag <= 1'b0;
end
else if(end_cnt_s)begin
flag <= ~flag;//1s取反
end
else begin
flag <= flag;
end
end
always @(posedge clk or negedge rst_n)begin
if(!rst_n)begin
led <= 4'b0;
end
else begin
if(flag)begin//亮pwm
led <= {cnt_s > cnt_ms, cnt_s > cnt_ms,cnt_s > cnt_ms,cnt_s > cnt_ms};
end
else begin//灭pwm
led <= {cnt_s < cnt_ms, cnt_s < cnt_ms,cnt_s < cnt_ms,cnt_s < cnt_ms};
end
end
end
endmodule三、引脚分配
