Espresso heuristic logic minimizer

The ESPRESSO logic minimizer is a computer program using heuristic and specific algorithms for efficiently reducing the complexity of digital logic gate circuits. ESPRESSO-I was originally developed at IBM by Robert K. Brayton et al. in 1982. and improved as ESPRESSO-II in 1984. Richard L. Rudell later published the variant ESPRESSO-MV in 1986 and ESPRESSO-EXACT in 1987. Espresso has inspired many derivatives. Electronic devices are composed of numerous blocks of digital circuits, the combination of which performs the required task. The efficient implementation of logic functions in the form of logic gate circuits (such that no more logic gates are used than are necessary) is necessary to minimize production costs, and/or maximize a device's performance. All digital systems are composed of two elementary functions: memory elements for storing information, and combinational circuits that transform that information. State machines, like counters, are a combination of memory elements and combinational logic circuits. Since memory elements are standard logic circuits they are selected out of a limited set of alternative circuits; so designing digital functions comes down to designing the combinational gate circuits and interconnecting them. In general the instantiation of logic circuits from high-level abstraction is referred to as logic synthesis, which can be carried out by hand, but usually some formal method by computer is applied. In this article the design methods for combinational logic circuits are briefly summarized. The starting point for the design of a digital logic circuit is its desired functionality, having derived from the analysis of the system as a whole, the logic circuit is to make part of. The description can be stated in some algorithmic form or by logic equations, but may be summarized in the form of a table as well. The below example shows a part of such a table for a 7-segment display driver that translates the binary code for the values of a decimal digit into the signals that cause the respective segments of the display to light up.