Editing Digital electronics (section)

===Register transfer systems===
[[File:Register transfer level - example toggler.svg|right|thumb|300px|Example of a simple circuit with a toggling output. The inverter forms the [[combinational logic]] in this circuit, and the register holds the state.]]

Many digital systems are [[Dataflow architecture|data flow machine]]s. These are usually designed using synchronous [[Register transfer level|register transfer logic]] and written with [[hardware description language]]s such as [[VHDL]] or [[Verilog]].

In register transfer logic, binary numbers are stored in groups of flip flops called [[processor register|register]]s. A sequential state machine controls when each register accepts new data from its input. The outputs of each register are a bundle of wires called a ''[[computer bus|bus]]'' that carries that number to other calculations. A calculation is simply a piece of combinational logic. Each calculation also has an output bus, and these may be connected to the inputs of several registers. Sometimes a register will have a [[multiplexer]] on its input so that it can store a number from any one of several buses.{{efn|Alternatively, the outputs of several items may be connected to a bus through [[3-state|buffer]]s that can turn off the output of all of the devices except one.}}

Asynchronous register-transfer systems (such as computers) have a general solution. In the 1980s, some researchers discovered that almost all synchronous register-transfer machines could be converted to asynchronous designs by using first-in-first-out synchronization logic. In this scheme, the digital machine is characterized as a set of data flows. In each step of the flow, a synchronization circuit determines when the outputs of that step are valid and instructs the next stage when to use these outputs.{{citation needed|date=October 2020}}