Editing Feedback (section)

====Latches and flip-flops====
[[File:JohnsonCounter2.png|thumb|A 4-bit [[ring counter]] using [[Flip-flop (electronics)#D flip-flop|D-type flip flops]]]]

A latch or a [[Flip-flop (electronics)|flip-flop]] is a [[electronic circuit|circuit]] that has two stable states and can be used to store state information. They typically constructed using feedback that crosses over between two arms of the circuit, to provide the circuit with a state. 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]]. Latches and flip-flops are fundamental building blocks of [[digital electronics]] systems used in computers, communications, and many other types of systems.

Latches and flip-flops are used as data storage elements. Such data storage can be used for storage of ''[[state (computer science)|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 [[clock signal|clock]]ed (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''.<ref name="pedroni">
{{cite book| author = Volnei A. Pedroni| title = Digital electronics and design with VHDL| url = https://books.google.com/books?id=-ZAccwyQeXMC| year = 2008| publisher = Morgan Kaufmann| isbn = 978-0-12-374270-4| page = 329 }}</ref><ref name="ee42">[http://rfic.eecs.berkeley.edu/ee100/pdf/lect24.pdf Latches and Flip Flops] {{Webarchive|url=https://web.archive.org/web/20161005192018/http://rfic.eecs.berkeley.edu/ee100/pdf/lect24.pdf |date=5 October 2016 }} (EE 42/100 Lecture 24 from Berkeley)  ''"...Sometimes the terms flip-flop and latch are used interchangeably..."''</ref>

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.