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In digital circuit theory, combinational logic (sometimes also referred to as time-independent logic〔 C.J. Savant, Jr.; Martin Roden; Gordon Carpenter. "Electronic Design: Circuits and Systems". 1991. ISBN 0-8053-0285-9 p. 682 〕 ) is a type of digital logic which is implemented by Boolean circuits, where the output is a pure function of the present input only. This is in contrast to sequential logic, in which the output depends not only on the present input but also on the history of the input. In other words, sequential logic has ''memory'' while combinational logic does not. Combinational logic is used in computer circuits to perform Boolean algebra on input signals and on stored data. Practical computer circuits normally contain a mixture of combinational and sequential logic. For example, the part of an arithmetic logic unit, or ALU, that does mathematical calculations is constructed using combinational logic. Other circuits used in computers, such as half adders, full adders, half subtractors, full subtractors, multiplexers, demultiplexers, encoders and decoders are also made by using combinational logic. An alternate term is combinatorial logic,〔Clive Maxfield. ("FPGAs: World Class Designs" ). p. 70. 2009. ISBN 1856176215〕 though this usage may be considered controversial.〔Cliff Cummings. ("Common Mistakes In Technical Texts" ). 2009.〕 ==Representation== Combinational logic is used to build circuits that produce specified outputs from certain inputs. The construction of combinational logic is generally done using one of two methods: a sum of products, or a product of sums. A sum of products can be visualized in a truth table, as in this example: Using sum of products, all logical statements which yield true results are summed, giving the result: : Using Boolean algebra, the result simplifies to the following equivalent of the truth table: : 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Combinational logic」の詳細全文を読む スポンサード リンク
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