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 inputs and will have one or two outputs. It is the basic storage element in sequential logic . Flip-flops and latches are fundamental building blocks 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 blinds with 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 to both flip-flops and flip-flops, the flip-flop is exclusively for discussing clocked circuits; The simple ones are commonly called latches .  
Using this terminology, a latch is level-sensitive, but 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 of clock edge.
The first electronic flip-flop was invented in 1918 by the British physicists William Eccles and FW Jordan .   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.
According to PL Lindley, an engineer at the Jet Propulsion Laboratory , the flip-flop types detailed below (SR, D, T, JK) were first discussed in a 1954 UCLA race on computer design by Montgomery Phister Book Logical Design of Digital Computers.   Lindley was at the time working at Hughes Aircraft under Eldred Nelson, who had cornered 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 JK. 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. 
- ^ Jump up to:a b Pedroni, Volnei A. (2008). Digital electronics and design with VHDL. Morgan Kaufmann. p. 329. ISBN 978-0-12-374270-4 .
- ^ Jump up to:a b Latches and Flip Flops (EE 42/100 Play 24 from Berkeley) “… Sometimes the terms flip-flop and latch are used interchangeably …”
- Jump up^ William Henry Eccles and Frank Wilfred Jordan, “Improvements in ionic relays” British patent number: GB 148582 (filed: 21 June 1918; published: 5 August 1920).
- Jump up^ See:
- WH Eccles and FW Jordan (19 September 1919) “A trigger relay utilizing three-electrode thermionic vacuum tubes,” The Electrician , 83 : 298.
- Reprinted in: Radio Review , 1 (3): 143-146 (December 1919).
- Summary in: WH Eccles and FW Jordan (1919) “A trigger relay using three electrode thermionic vacuum tubes,” Report of the Eighty-seventh Meeting of the British Association for the Advancement of Science: Bournemouth: 1919, September 9-13 , pp . 271-272.
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- Jump up^ PL Lindley, Aug. 1968,EDN (magazine), (letter dated June 13, 1968).
- Jump up^ Phister, Montgomery (1958). Logical Design of Digital Computers.Wiley. p. 128.
- Jump up^ US 2850566 , Eldred C. Nelson, “High-Speed Printing System”, published Sept. 8, 1953, issued Sept. 2, 1958; Page 15
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- Jump up^ The D Flip-Flop
- Jump up^ Edge-Triggered Flip-flops
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- Jump up^ Chaney, Thomas J .; Molnar, Charles E. (April 1973). “Anomalous Behavior of Synchronizer and Arbiter Circuits” . IEEE Transactions on Computers . C-22 (4): 421-422. ISSN 0018-9340 . Doi : 10.1109 / TC.1973.223730 .
- Jump up^ Often Attributed ToDon Knuth(1969) (seeMidhat J. Gazalé (2000).Number: from Ahmose to Cantor .. Princeton University Press, p 57.ISBN 978-0-691-00515-7 .), The Termflip-flap-flop, for example,Bowdon, Edward K. (1960). The design and application of a “flip-flap-flop” using tunnel diodes (Master’s thesis) . University of North Dakota. , And inAlexander, W. (Feb 1964). “The ternary computer” . Electronics and Power . EIT. 10 (2): 36-39. Doi : 10.
- Jump up^ “Ternary” flip-flap-flop ” ” .
- Jump up^ US 6975152
- Jump up^ Irving, Thurman A .; Shiva, Sajjan G .; Nagle, H. Troy (March 1976). “Flip-Flops for Multiple-Valued Logic”. Computers, IEEE Transactions on . C-25 (3): 237-246. Doi : 10.1109 / TC.1976.5009250 .
- Jump up^ Wu, Haomin; Zhuang Nan (1991). “Research into ternary edge-triggered JKL flip-flop”. Journal of Electronics (China) . 8 (Volume 8, Number 3 / July, 1991): 268-275. Doi : 10.1007 / BF02778378 .