main.c 程式原始碼：

// =========================== main.c ======================

#include "reg51.h"

#define LED_ON  20
#define LED_OFF 0
#define F_1HZ   1
#define F_2HZ   2
#define F_3HZ   3
#define F_4HZ   4
#define F_5HZ   5
#define F_6HZ   6
#define F_7HZ   7
#define F_8HZ   8
#define F_9HZ   9
#define
 
 F_10HZ  10

sbit LED1 = P2.0;                   // 定義LED IO口

unsigned char g_u8_LedFrequence;    // 按鍵值
unsigned char g_flag_10ms_led;      // 10ms 計時標誌


//LED 以不同頻率閃爍
//LED 亮的時間是：100ms
//LED 滅的時間是：相應週期 - 100ms
//LED 頻率的範圍：0-10 hz
void LED1_Flash(unsigned char flash_frequence)
{
    static byte count, flash_period;

    //根據頻率選擇週期
 

    switch(flash_frequence)
    {
        case F_1HZ :    flash_period = 100; break;      //1 hz
        case F_2HZ :    flash_period = 50;  break;      //2 hz
        case F_3HZ :    flash_period = 34;  break;      //3 hz
        case F_4HZ :    flash_period = 25;  break;      //4 hz
        case F_5HZ :    flash_period = 20
 
;  break;      //5 hz
        case F_6HZ :    flash_period = 17;  break;      //6 hz
        case F_7HZ :    flash_period = 14;  break;      //7 hz
        case F_8HZ :    flash_period = 12;  break;      //8 hz
        case F_9HZ :    flash_period = 11;  break;      //9 hz
        case F_10HZ :   flash_period = 10;  break;      //10 hz
        case LED_ON:    count = 0;          break;      //led on
        case LED_OFF:   count = 9;          break;      //led off
    }

    //根據週期閃爍
    if(g_flag_10ms_led)                                 //此標誌在中斷服務程式中，每10ms置一一次。
    {
        g_flag_10ms_led = 0;                            //清零 led的10ms計數標誌，

        count++;                                        //計數器

        if(count==1)            LED1 = 1;               //點亮LED LED亮的時間：1-10 
        else if(count == 10)    LED1 = 0;               //熄滅LED LED滅的時間：10-flash_period
        else if(count >= flash_period)  count = 0;      //清零計數
    }
}


void LED1_Flash(unsigned char flash_frequence);         // 宣告LED flash函式


void T0_Init_10ms(void)                                 // timer0，初始化函式 ，定時時間為 10ms
{
    TMOD |= 0x01;
    TH0 = (65535 - 10000)/256;
    TL0 = (65535 - 10000)%256;

    ET0 = 1;
    TR0 = 1;
    EA = 1;
}

// ================================================  主函式 ===================================================
void main(void)
{
    P1.0 = 1;                                           // P1.0 拉高
    T0_Init_10ms();                                     // 定時器0，初始化，定時10ms

    g_u8_LedFrequence = F_3HZ;                          // 設定LED閃爍的頻率值，3hz

    while(1)
    {
        LED1_Flash(g_u8_LedFrequence);                  // LED閃爍
    }
}

// timer0 中斷服務程式
void IRQ_T0(void) interrupt 1
{
    g_flag_10ms_led = 1;                                // 置位 10ms 定時標誌
}