12.3 Combinational circuits
Combinational circuits are digital circuits that do not involve any kind of feedback. In other words, the output of a combinational circuit cannot be fed back into that circuit as input. In this section we’ll talk about a number of combinational circuits that are used in the construction of digital computers. These circuits include comparators, adders, decoders, encoders, multiplexers, and demultiplexers. First, we begin with a relatively simply circuit, the “exclusive or” or xor .