说明：  实验四(第二版)：用 Atmega8 实现D触发锁存器的功能 实现目的： 1． 管脚设定为输入时，了解如何可以编程设定上拉电阻。 2． 如何使用软件控制取样频率及时间，达到一定的抗干扰目的 3． 为了让程序运行更稳定，防止跑飞，如何使用看门狗？
(Experiment IV (second edition): The Atmega8 trigger D latches realize the function of the realization of the purpose of: 1. Pin set to input can be programmed to understand how to set pull-up resistor. 2. How to use the software to control the sampling frequency and time to achieve the purposes of certain anti-interference 3. In order to allow program to run more stable and prevent the running to fly, how to use the watchdog?)