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+/*
+ * name: homework7.h
+ * author: msksbr
+ * date: 2025/05/22
+ * description: a header file for homework7(a 51 MCU lesson homework)
+ * version: 1.0
+ * variables:
+ *    1.0:
+ *        1. pin numbers for BUS of leds, segs and matrix led
+ *        2. pin numbers for BUS of 74HC138
+ * functions:
+ *    1.0:
+ *        1. 74HC138 switcher
+ *        2. timer by ms based on timer0 with mode 1
+ */
+
+#include <REG52.H>
+
+// variables:
+// 1. pin numbers for BUS of leds, segs and matrix led
+sbit DB0 = P0 ^ 0;
+sbit DB1 = P0 ^ 1;
+sbit DB2 = P0 ^ 2;
+sbit DB3 = P0 ^ 3;
+sbit DB4 = P0 ^ 4;
+sbit DB5 = P0 ^ 5;
+sbit DB6 = P0 ^ 6;
+sbit DB7 = P0 ^ 7;
+// 2. pin numbers for BUS of 74HC138
+sbit ADDR0 = P1 ^ 0; // @param ADDR0: to A(A0) of 74HC138
+sbit ADDR1 = P1 ^ 1; // @param ADDR1: to B(A1) of 74HC138
+sbit ADDR2 = P1 ^ 2; // @param ADDR2: to C(A2) of 74HC138
+
+sbit ADDR3 = P1 ^ 3; // @param ADDR3: to E1 of 74HC138
+sbit ENLED = P1 ^ 4; // @param ENLED: to E2 & E3 of 74HC138
+
+// functions:
+// 1. 74HC138 switcher
+void switch_38(unsigned char n)
+{
+    // @subsection: turn n to 3 bits of binary number
+    bit A0 = n & 0x01;
+    bit A1 = (n >> 1) & 0x01;
+    bit A2 = (n >> 2) & 0x01;
+    // @subsection: turn on 74HC138
+    ENLED = 0;
+    ADDR3 = 1;
+    // @subsection: add 3 bits of binary number to 74HC138
+    ADDR0 = A0;
+    ADDR1 = A1;
+    ADDR2 = A2;
+}
+// 2. timer by ms based on timer0 with mode 1
+void timer0_mode1(unsigned int ms)
+{
+    unsigned int i;
+    // @subsection: set timer0 to mode 1
+    TMOD = 0x01;
+    // @subsection: set timer0 to 11.0592MHz
+    TH0 = 0xFC;
+    TL0 = 0x67;
+    // @subsection: start timer0
+    TR0 = 1;
+    // @subsection: wait for timer0 to count ms times
+    for (i = 0; i < ms; i++) {
+        while (!TF0);
+        TF0 = 0;
+        TH0 = 0xFC;
+        TL0 = 0x67;
+    }
+    // @subsection: stop timer0
+    TR0 = 0;
+}
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