diff --git a/homework6/src/homework6.h b/homework6/src/homework6.h
index bd5201f..3f046c5 100644
--- a/homework6/src/homework6.h
+++ b/homework6/src/homework6.h
@@ -1 +1,68 @@
 // homework6.h
+/*
+ * this is the header file to
+ * define the
+ * variables:
+ * - pins for the LEDs and the segs
+ * - pins for the 38 transistors
+ * - seg chars to display to display the number
+ * functions:
+ * - set the 38 transistors.
+ */
+
+#include <REG52.H>
+
+// variables:
+// pins for the LEDs and the segs
+sbit BUS1A  = P2 ^ 0; // Red LED and A Seg
+sbit BUS2B  = P2 ^ 1; // Orange LED and B Seg
+sbit BUS3C  = P2 ^ 2; // Yellow LED and C Seg
+sbit BUS4D  = P2 ^ 3; // Green LED and D Seg
+sbit BUS5E  = P2 ^ 4; // Aqua LED and E Seg
+sbit BUS6F  = P2 ^ 5; // BLUE LED and F Seg
+sbit BUS7G  = P2 ^ 6; // Purple LED and G Seg
+sbit BUS8DP = P2 ^ 7; // White LED and DP Seg
+// pins for the 38 transistors
+sbit ADDR0 = P1 ^ 0; // to A(A0)
+sbit ADDR1 = P1 ^ 1; // to B(A1)
+sbit ADDR2 = P1 ^ 2; // to C(A2)
+sbit ADDR3 = P1 ^ 3; // to E1
+sbit ENLED = P1 ^ 4; // to E2 & E3
+// seg chars to display to display the number
+unsigned char code LedChar[] = {
+    0xC0,
+    0xF9,
+    0XA4,
+    0XB0,
+    0X99,
+    0X92,
+    0X82,
+    0XF8,
+    0X80,
+    0X90,
+    0X88,
+    0X83,
+    0XC6,
+    0XA1,
+    0X86,
+    0X8E,
+};
+// functions:
+// 38 transistors control function
+/*
+ * param:
+ * - addr: the address of the 38 transistors.
+ * function:
+ * - Convert the address to 3 binary numbers.
+ * - Set the 38 transistors to the address.
+ */
+void set38(unsigned char addr)
+{
+    // Enable the 38 transistors.
+    ENLED = 0;
+    ADDR3 = 1;
+    // Set the 38 transistors to the address.
+    ADDR0 = addr & 0x01;
+    ADDR1 = (addr & 0x02) >> 1;
+    ADDR2 = (addr & 0x04) >> 2;
+}
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