diff --git a/homework6/.eide/eide.json b/homework6/.eide/eide.json
index 8d94045..1a60965 100644
--- a/homework6/.eide/eide.json
+++ b/homework6/.eide/eide.json
@@ -19,7 +19,8 @@
   "targets": {
     "Debug": {
       "excludeList": [
-        "src/test1.c"
+        "src/test1.c",
+        "src/test2.c"
       ],
       "toolchain": "Keil_C51",
       "compileConfig": {
diff --git a/homework6/homework6.code-workspace b/homework6/homework6.code-workspace
index 8c192af..2a97a15 100644
--- a/homework6/homework6.code-workspace
+++ b/homework6/homework6.code-workspace
@@ -18,7 +18,8 @@
             "*.c++": "cpp",
             "*.cpp": "cpp",
             "*.cxx": "cpp",
-            "*.cc": "cpp"
+            "*.cc": "cpp",
+            "REG52.H": "cpp"
         },
         "[yaml]": {
             "editor.insertSpaces": true,
diff --git a/homework6/src/homework6.h b/homework6/src/homework6.h
index 07af757..1020ccd 100644
--- a/homework6/src/homework6.h
+++ b/homework6/src/homework6.h
@@ -69,4 +69,5 @@ void set38(unsigned char addr)
     ADDR0 = addr & 0x01;
     ADDR1 = (addr & 0x02) >> 1;
     ADDR2 = (addr & 0x04) >> 2;
-}
\ No newline at end of file
+}
+// low seg is the right side.
\ No newline at end of file
diff --git a/homework6/src/test3.c b/homework6/src/test3.c
new file mode 100644
index 0000000..6bf1c74
--- /dev/null
+++ b/homework6/src/test3.c
@@ -0,0 +1,50 @@
+// test3.c
+// 通过定时器T1中断，实现三位数秒表
+// make a three-digit stopwatch by timer T1 interrupt.
+#include "homework6.h"
+
+unsigned char digits[3]  = {0, 0, 0}; // store the three digits of the stopwatch.
+unsigned char displayPos = 0;         // store the position of the display.
+
+void test3()
+{
+    TMOD = 0x10; // set the timer 1 to mode 1.
+    TH1  = 0xFC; // set the timer 1 to 1s.
+    TL1  = 0x18; // set the timer 1 to 1s.
+    TR1  = 1;    // start the timer 1.
+    ET1  = 1;    // enable the timer 1 interrupt.
+    EA   = 1;    // enable the interrupt.
+    while (1);
+}
+void Timer1_ISR() interrupt 3
+{
+    static unsigned int counter = 0;      // counter to count the number of interrupts.
+    TH1                         = 0xFC;   // reset the timer 1.
+    TL1                         = 0x18;   // reset the timer 1.
+    set38(displayPos);                    // set the 38 transistors to the address.
+    P2 = LedChar[digits[2 - displayPos]]; // display the digit.
+    displayPos++;                         // switch to the next digit.
+    if (displayPos >= 3) displayPos = 0;  // if the display position is 3, reset the display position to 0.
+    if (++counter >= 1000) {
+        counter = 0; // reset the counter.
+        if (++digits[2] >= 10) {
+            digits[2] = 0; // reset the third digit.
+            if (++digits[1] >= 10) {
+                digits[1] = 0; // reset the second digit.
+                if (++digits[0] >= 10) {
+                    digits[0] = 0; // reset the first digit.
+                }
+            }
+        }
+    }
+    // reset the stopwatch when the stopwatch is 999.
+    if (digits[0] == 9 && digits[1] == 9 && digits[2] == 9) {
+        digits[0] = 0;
+        digits[1] = 0;
+        digits[2] = 0;
+    }
+}
+void main()
+{
+    test3();
+}
\ No newline at end of file