2.7 代数简化在上一节中,我们看到任何组合逻辑函数都可以用两种标准形式来表达,然后用两级电路来实现标准表达式,但是,这样的电路通常并不是实现逻辑函数的最经济的方法。在下面三节中我们要讨论使逻辑函数简化或者最佳化的方法以期达到最经济的效果。“简化”意味着寻找项数最少或者字母最少的表达式。“最佳化”则是意味着寻找最能适应某些简化规定的表达式。通常,我们总是先试图使表达式的项数减到最少,然后才是字母数。这种方式相当于先减少逻辑门的数目,然后再使输入端数亦减到 Algebraic Simplification In the previous section, we saw that any combinatorial logic function can be expressed in two standard forms, and then use standard two-stage circuit expressions, but such circuits are usually not the most logical function Economic method. In the next three sections we discuss ways to simplify or optimize logic functions in order to achieve the most economical results. “Simplify” means looking for expressions with the fewest items or the least letters. “Optimize” means finding expressions that best fit some simplification rules. Often, we always try to minimize the number of expressions before we start with the number of letters. This approach is equivalent to reducing the number of logic gates before reducing the number of inputs