diff --git a/led_matrix/tb_lm_2.v b/led_matrix/tb_lm_2.v
index cd711c6..05cf7b0 100644
--- a/led_matrix/tb_lm_2.v
+++ b/led_matrix/tb_lm_2.v
@@ -97,7 +97,7 @@ always @(posedge sys_clk or negedge sys_rst) begin
     end
 end
 
-
+// 异步信号, 通过比较上次时钟周期的状态和当前时钟周期的状态得到当前是否按下了
 always @(posedge sys_clk or negedge sys_rst) begin
     if (sys_rst == 1'b0) begin
         key <= 1'b0;