以下是一个用Verilog编写的数码管闪烁代码。在接收到第三个按键按下的信号时，数码管将反转并开始倒计时。倒计时完成后，数字9将重新出现并重新开始闪烁。

module blinker(
input clk,
input [2:0] button,
output reg [3:0] seg,
output reg [3:0] anode
);

reg [29:0] timer;
reg flip;

always @ (posedge clk) begin
if(button == 3'b100) begin // 如果接收到第三个按键按下的信号
timer <= 30_000_000; // 将计时器设定为30秒
flip <= 1; // 数码管反转
end
else if(timer > 0) begin // 如果正在倒计时
timer <= timer - 1;
if(timer == 0) begin // 倒计时完成
seg <= 4'b1001; // 数码管显示9
flip <= 0; // 数码管恢复正常状态
end
end
else begin // 正常闪烁
timer <= 30_000_000;
flip <= ~flip;
end
end

always @ (posedge clk) begin
if(flip) begin
case(seg)
4'b0001: seg <= 4'b1000;
4'b1000: seg <= 4'b0001;
default: seg <= 4'b0001;
end
end
else begin
case(seg)
4'b0001: seg <= 4'b0010;
4'b0010: seg <= 4'b0100;
4'b0100: seg <= 4'b1000;
4'b1000: seg <= 4'b0001;
default: seg <= 4'b0001;
end
end
end

always @ (posedge clk) begin
case(anode)
2'b00: anode <= 2'b01;
2'b01: anode <= 2'b10;
2'b10: anode <= 2'b11;
default: anode <= 2'b00;
end
end

endmodule