关于上拉电阻和下拉电阻的解释及其应用，虽然很常用但是也容易被忽略。-On the pull-up resistor and pull-down resistor interpretation and its application, although a very common but easily ignored.

对上拉电阻的作用作了比较全面的总结，不错的参考资料-The role of the pull-up resistor made a more comprehensive summary, a good reference for