完成一位二进制全减器的设计，采用原理图输入法和文本输入法分别实现，分层设计，底层由半加器（也用原理图输入法）和逻辑门组成-Completion of a binary full subtracter design, the use of schematic and text input method input method were realized, hierarchical design, the bottom of the half adder (also used schematic