Editing Digital electronics (section)

===Representation===
A digital circuit's input-output relationship can be represented as a [[truth table]]. An equivalent high-level circuit uses [[logic gate]]s, each represented by a different shape (standardized by [[IEEE]]/[[ANSI]] 91–1984).<ref>Maini. A.K. (2007). Digital Electronics Principles, Devices and Applications. Chichester, England.: John Wiley & Sons Ltd.</ref> A low-level representation uses an equivalent circuit of electronic switches (usually [[transistor]]s).

Most digital systems divide into [[combinational]] and [[Sequential logic|sequential system]]s. The output of a combinational system depends only on the present inputs. However, a sequential system has some of its outputs fed back as inputs, so its output may depend on past inputs in addition to present inputs, to produce a ''sequence'' of operations. Simplified representations of their behavior called [[state machine]]s facilitate design and test.

Sequential systems divide into two further subcategories. [[synchronous system|"Synchronous" sequential system]]s change state all at once when a [[clock signal]] changes state. [[asynchronous system|"Asynchronous" sequential system]]s propagate changes whenever inputs change. Synchronous sequential systems are made using [[flip-flop (electronics)|flip flop]]s that store inputted voltages as a [[bit]] only when the clock changes.