diff --git a/homework7/.eide/eide.json b/homework7/.eide/eide.json
index d853fa5..68db7d4 100644
--- a/homework7/.eide/eide.json
+++ b/homework7/.eide/eide.json
@@ -21,7 +21,8 @@
       "excludeList": [
         "src/test1.c",
         "src/test2.c",
-        "src/test3.c"
+        "src/test3.c",
+        "src/test4.c"
       ],
       "toolchain": "Keil_C51",
       "compileConfig": {
diff --git a/homework7/src/test5.c b/homework7/src/test5.c
new file mode 100644
index 0000000..1caf8fa
--- /dev/null
+++ b/homework7/src/test5.c
@@ -0,0 +1,65 @@
+/*
+ * @name: test5.c
+ * @author: msksbr
+ * @date: 2025-05-25
+ * @description: a test for homework7's homework tests
+ * @version: 1.0
+ * homework zh_CN: 基于点阵的 9 到 0 的倒计时秒表显示
+ * homework EN: display a countdown timer on the led matrix from 9 to 0
+ */
+
+#include "homework7.h"
+
+unsigned char code number_char[10][8] = {
+    {0x70, 0xd8, 0xd8, 0xd8, 0xd8, 0xd8, 0x70, 0x00}, // 0
+    {0x30, 0xf0, 0x30, 0x30, 0x30, 0x30, 0xf8, 0x00}, // 1
+    {0xf0, 0xd8, 0x18, 0x38, 0x70, 0xe0, 0xf8, 0x00}, // 2
+    {0xf0, 0xd8, 0x18, 0x78, 0x18, 0xd8, 0xf0, 0x00}, // 3
+    {0x30, 0x30, 0x70, 0xf0, 0xf8, 0x30, 0x30, 0x00}, // 4
+    {0xf8, 0xc0, 0xf0, 0x18, 0x18, 0xd8, 0xf0, 0x00}, // 5
+    {0x78, 0xe0, 0xf0, 0xd8, 0xd8, 0xf8, 0x70, 0x00}, // 6
+    {0xf8, 0x18, 0x38, 0x30, 0x70, 0x60, 0x60, 0x00}, // 7
+    {0x70, 0xd8, 0xf8, 0xf8, 0xd8, 0xd8, 0x70, 0x00}, // 8
+    {0x70, 0xd8, 0xd8, 0xd8, 0x78, 0x38, 0xf0, 0x00}  // 9
+};
+
+void test5()
+{
+    TMOD = 0x10;
+    TH1  = 0xFC;
+    TL1  = 0x18;
+    TR1  = 1;
+    ET1  = 1;
+    EA   = 1;
+    while (1);
+}
+
+void timer1_ISR() interrupt 3
+{
+    static unsigned char i           = 0;
+    static unsigned int count        = 0;
+    static unsigned char current_num = 9;
+
+    TH1 = 0xFC;
+    TL1 = 0x18;
+
+    P2 = 0xFF;
+    switch_138(i);
+    P2 = ~number_char[current_num][i];
+
+    if (++i >= 8) i = 0;
+
+    if (++count >= 1000) {
+        count = 0;
+        if (current_num > 0) {
+            current_num--;
+        } else {
+            current_num = 9;
+        }
+    }
+}
+
+void main()
+{
+    test5();
+}
\ No newline at end of file