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In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. A flip-flop is a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic. Flip-flops and latches are a fundamental building block of digital electronics systems used in computers, communications, and many other types of systems. Flip-flops and latches are used as data storage elements. A flip-flop stores a single ''bit'' (binary digit) of data; one of its two states represents a "one" and the other represents a "zero". Such data storage can be used for storage of ''state'', and such a circuit is described as sequential logic. When used in a finite-state machine, the output and next state depend not only on its current input, but also on its current state (and hence, previous inputs). It can also be used for counting of pulses, and for synchronizing variably-timed input signals to some reference timing signal. Flip-flops can be either simple (transparent or opaque) or clocked (synchronous or edge-triggered). Although the term flip-flop has historically referred generically to both simple and clocked circuits, in modern usage it is common to reserve the term ''flip-flop'' exclusively for discussing clocked circuits; the simple ones are commonly called ''latches''.〔〔 Using this terminology, a latch is level-sensitive, whereas a flip-flop is edge-sensitive. That is, when a latch is enabled it becomes transparent, while a flip flop's output only changes on a single type (positive going or negative going) of clock edge. ==History== The first electronic flip-flop was invented in 1918 by the British physicists William Eccles and F. W. Jordan.〔William Henry Eccles and Frank Wilfred Jordan, "(Improvements in ionic relays )" British patent number: GB 148582 (filed: 21 June 1918; published: 5 August 1920).〕〔W. H. Eccles and F. W. Jordan (19 September 1919) "A trigger relay utilizing three-electrode thermionic vacuum tubes," ''The Electrician'', vol. 83, page 298. Reprinted in: ''Radio Review'', vol. 1, no. 3, pages 143–146 (December 1919).〕 It was initially called the ''Eccles–Jordan trigger circuit'' and consisted of two active elements (vacuum tubes).〔 〕 The design was used in the 1943 British Colossus codebreaking computer and such circuits and their transistorized versions were common in computers even after the introduction of integrated circuits, though flip-flops made from logic gates are also common now.〔 〕〔 〕 Early flip-flops were known variously as trigger circuits or multivibrators. According to P. L. Lindley, an engineer at the US Jet Propulsion Laboratory, the flip-flop types detailed below (RS, D, T, JK) were first discussed in a 1954 UCLA course on computer design by Montgomery Phister, and then appeared in his book ''Logical Design of Digital Computers.''〔P. L. Lindley, Aug. 1968, EDN (magazine), (letter dated June 13, 1968).〕〔 〕 Lindley was at the time working at Hughes Aircraft under Eldred Nelson, who had coined the term JK for a flip-flop which changed states when both inputs were on (a logical "one"). The other names were coined by Phister. They differ slightly from some of the definitions given below. Lindley explains that he heard the story of the JK flip-flop from Eldred Nelson, who is responsible for coining the term while working at Hughes Aircraft. Flip-flops in use at Hughes at the time were all of the type that came to be known as J-K. In designing a logical system, Nelson assigned letters to flip-flop inputs as follows: #1: A & B, #2: C & D, #3: E & F, #4: G & H, #5: J & K. Nelson used the notations "''j''-input" and "''k''-input" in a patent application filed in 1953.〔 ; (page 15 )〕 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「Flip-flop (electronics)」の詳細全文を読む スポンサード リンク
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