Digital Integrated Circuit Design Using Verilog and Systemverilog

Appendix B

Standard combinational and sequential functions

Digital circuits operate in binary. Signals have only two legal states, true or false, also called logic one and logic zero. The electrical characteristics of logic one and logic zero vary. At the dawn of digital electronic circuitry, when vacuum tubes were used to implement logic functions, the difference between a true and a false signal would be tens of volts. For modern semiconductors, it is less than 1 V. Use of the abstract true and false allows logic systems to be designed and built without specifying the electrical characteristics of each signal.

Combinational functions

The most fundamental building blocks of all digital circuit are the Boolean operators AND, OR, Exclusive ...