diff --git a/homework4/.eide/eide.json b/homework4/.eide/eide.json
index a73c9ae..0f7e955 100644
--- a/homework4/.eide/eide.json
+++ b/homework4/.eide/eide.json
@@ -20,7 +20,8 @@
     "Debug": {
       "excludeList": [
         "src/test1.c",
-        "src/test2.c"
+        "src/test2.c",
+        "src/test3.c"
       ],
       "toolchain": "Keil_C51",
       "compileConfig": {
diff --git a/homework4/homework4.pdsprj b/homework4/homework4.pdsprj
index 895e80b..1b2b9de 100644
Binary files a/homework4/homework4.pdsprj and b/homework4/homework4.pdsprj differ
diff --git a/homework4/src/test4.c b/homework4/src/test4.c
new file mode 100644
index 0000000..59f2b2f
--- /dev/null
+++ b/homework4/src/test4.c
@@ -0,0 +1,40 @@
+// test4.c
+// 使用定时器来实现左右移动的流水灯（每过0.5秒，切换一个小灯）；
+#include "homework4.h"
+
+unsigned char cnt = 0; // 定时器溢出计数
+unsigned char led = 0; // 当前亮灯
+
+void test4()
+{
+    set_38_2LED();
+    TMOD = 0x01; // timer T0 mode 1, 16-bit timer
+    TH0  = 0XB8;
+    TL0  = 0X00;
+    TR0  = 1; // timer T0 run
+
+    while (1) {
+        if (TF0 == 1) { // timer T0 overflow
+            TF0 = 0;    // clear timer T0 overflow flag
+            TH0 = 0xB8; // reload timer T0 value
+            TL0 = 0x00;
+            cnt++; // log timer T0 overflow counts
+            if (cnt >= 50) {
+                cnt = 0; // clear log timer T0 overflow counts
+                if (led < 8) {
+                    P2 = ~(0X01 << led);
+                } else {
+                    P2 = ~(0X80 >> (led - 8));
+                }
+                led++;
+                if (led >= 16) {
+                    led = 0;
+                }
+            }
+        }
+    }
+}
+void main()
+{
+    test4();
+}
\ No newline at end of file