Flip-flop (electronics)

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 . [1] [2]

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.


Flip-flop schematics from the Eccles and Jordan patent filed 1918, one-shot with a positive feedback path, and the other as a symmetric cross-coupled pair

The first electronic flip-flop was invented in 1918 by the British physicists William Eccles and FW Jordan . [3] [4] It was initially called the Eccles-Jordan trigger circuit and consisted of two active elements ( vacuum tubes ). [5] The design was used in the 1943 British Colossus codebreaking computer [6] 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. [9] [10] 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. [11]


  1. ^ 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 .
  2. ^ 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 …”
  3. 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).
  4. 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.
  5. Jump up^ Pugh, Emerson W .; Johnson, Lyle R .; Palmer, John H. (1991). IBM’s 360 and early 370 systems . MIT Press. p. 10. ISBN  978-0-262-16123-7.
  6. Jump up^ Flowers, Thomas H. (1983), “The Design of Colossus” , Annals of the History of Computing , 5 (3): 249, doi : 10.1109 / MAHC.1983.10079
  7. Jump up^ Gates, Earl D. (2000-12-01). Introduction to electronics (4th ed.). Delmar Thomson (Cengage) Learning. p. 299. ISBN  978-0-7668-1698-5 .
  8. Jump up^ Fogiel, Max; Gu, You-Liang (1998). The electronics problem solver, Volume 1 (revised ed.). Research & Education Assoc. p. 1223. ISBN  978-0-87891-543-9 .
  9. Jump up^ PL Lindley, Aug. 1968,EDN (magazine), (letter dated June 13, 1968).
  10. Jump up^ Phister, Montgomery (1958). Logical Design of Digital Computers.Wiley. p. 128.
  11. Jump up^ US 2850566 , Eldred C. Nelson, “High-Speed ​​Printing System”, published Sept. 8, 1953, issued Sept. 2, 1958; Page 15
  12. Jump up^ Shiva, Sajjan G. (2000). Computer design and architecture (3rd ed.). CRC Press. p. 81. ISBN  978-0-8247-0368-4 .
  13. Jump up^ Roth, Charles H. Jr. “Latches and Flip-Flops.” Fundamentals of Logic Design. Boston: PWS, 1995. Print.
  14. Jump up^ Langholz, Gideon; Kandel, Abraham; Mott, Joe L. (1998). Foundations of Digital Logic Design . Singapore: World Scientific Publishing Co. Ptc. Ltd. p. 344. ISBN  978-981-02-3110-1 .
  15. Jump up^ Hinrichsen, Diederich; Pritchard, Anthony J. (2006). Mathematical Systems Theory I: Modeling, State Space Analysis, Stability and Robustness . Springer. pp. 63-64. ISBN  9783540264101 .
  16. Jump up^ Farhat, Hassan A. (2004). Digital design and computer organization . 1 . CRC Press. p. 274. ISBN  978-0-8493-1191-8 .
  17. ^ Jump up to:a b Kogge, Peter M. (1981). The Architecture of Pipelined Computers . McGraw-Hill. pp. 25-27. ISBN  0-07-035237-2 .
  18. Jump up^ Cotten, LW (1965). “Implementation of High-Speed ​​Pipeline Systems”. AFIPS Proc. Fall Joint Computer Conference : 489-504. Doi : 10.1145 / 1463891.1463945 .
  19. Jump up^ Earle, J. (March 1965). “Latched Carry-Save Adder”. IBM Technical Disclosure Bulletin . 7 (10): 909-910.
  20. ^ Jump up to:a b Omondi, Amos R. (1999-04-30). The Microarchitecture of Pipelined and Superscalar Computers . Springer. pp. 40-42. ISBN  978-0-7923-8463-2 .
  21. ^ Jump up to:a b Kunkel, Steven R .; Smith, James E. (May 1986). “Optimal Pipelining in Supercomputers”. ACM SIGARCH Computer Architecture News . ACM. 14 (2): 404-411 [406]. CiteSeerX  . ISSN  0163-5964 . Doi : 10.1145 / 17356.17403 .
  22. Jump up^ The D Flip-Flop
  23. Jump up^ Edge-Triggered Flip-flops
  24. Jump up^ A Survey of Digital Computer Memory Systems
  25. Jump up^ SN7474 TI datasheet
  26. ^ Jump up to:a b Mano, Mr. Morris; Kime, Charles R. (2004). Logic and Computer Design Fundamentals, 3rd Edition . Upper Saddle River, NJ, USA: Pearson Education International. pp. pg283. ISBN  0-13-191165-1 .
  27. ^ Jump up to:a b Harris, S; Harris, D (2016). Digital Design and Computer Architecture. Morgan Kaufmann, Waltham, MA. ISBN  978-0-12-800056-4 .
  28. 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 .
  29. 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.
  30. Jump up^ “Ternary” flip-flap-flop ” ” .
  31. Jump up^ US 6975152
  32. 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 .
  33. 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 .

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