在对无关项输入所对应的输出进行分析时,教材上的方法是将无关项带入逻辑表达式,计算出结果。用带入逻辑表达式的方法比较麻烦,容易出错。本文提出了利用卡诺图观察的方法,直接观察出无关项对应的输出,无需计算可直接得出结果,该方法直观明了,不容易出错,使用非常方便。同时提出了利用圈“×”法可得到最简与或约束式的方法。 In the analysis of the output of the irrelevant items, the teaching method is to bring extraneous items into the logical expression to calculate the result. With the way to bring the logic of the more cumbersome and error-prone. In this paper, the method of using Karnaugh map is proposed to directly observe the output of unrelated items, and the result can be directly obtained without calculation. The method is intuitive, easy to make mistakes, and easy to use. At the same time, the method of using the circle “x ” method to get the simplest or constrained method is proposed.