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logic element[′läj·ik ‚el·ə·mənt]
the simplest unit of an electronic computer; performs a single specific logical operation on input signals according to the rules of the algebra of logic. Discrete values of the input and output signals are taken for the logic element, independent of their physical realization. There are usually two levels, which are conventionally taken as “0” and “1.” A distinction is made between combined logic elements, whose output signals at a certain moment are determined by combinations of the input signals operating at that moment, and storage (memory) or delay elements, for which the output signals are determined by the state of the logic element when the next signal is transmitted.
Among the combined logic elements are the inverter (NOT element), the coincidence gate (conjunctor, or AND element), and the disjunctor (OR element), which is a logic element with several inputs and a single output at which a signal appears when a signal is present on at least one of the inputs. Logic elements made from combinations of elements, such as the NOT AND (NAND) and the NOT OR (NOR) elements, are widely used. Threshold elements, such as majority elements, which operate according to the “majority principle” (if the signal “1” is fed to most of the inputs of an element, the signal “1” will also be set up at the output of the circuit), constitute a separate class of logic elements.
Logic elements are the fundamental elements for constructing logic circuits in computers and discrete automatic systems. A set of logic elements makes up the logical structure of a unit, subassembly, or device of the computer. The set of logic elements consisting of the AND, OR, and NOT elements, by means of which a logic design of any complexity may be constructed, is called functionally complete. There is a trend toward the creation of universal logic elements, which can execute a number of logic functions.
REFERENCESAnisimov, B. V., and V. N. Chetverikov. Osnovy teorii i proektirovaniia tsifrovykh vychislitel’nykh mashin. Moscow, 1962.
Vavilov, E. N., and G. P. Portnoi. Sintez skhem elektronnykh tsifrovykh mashin. Moscow, 1963.
A. V. GUSEV