
In electrical and electronic engineering, a daisy chain is a wiring scheme in which multiple devices are wired together in sequence or in a ring, similar to a
garland of daisy flowers. Daisy chains may be used for power, analog signals, digital data, or a combination thereof.
The term ''daisy chain'' may refer either to large scale devices connected in series, such as a series of
power strips
A power strip is a block of electrical sockets that attaches to the end of a flexible cable (typically with a mains plug on the other end), allowing multiple electrical devices to be powered from a single electrical socket. Power strips are often ...
plugged into each other to form a single long line of strips, or to the wiring patterns embedded inside of devices. Other examples of devices which can be used to form daisy chains are those based on
Universal Serial Bus (USB),
FireWire
IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple in cooperation with a number of companies, primarily Sony an ...
,
Thunderbolt and
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in ...
cables.
Signal transmission
For
analog signal
An analog signal or analogue signal (see spelling differences) is any continuous signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog audio signal, the instantaneous signal voltage vari ...
s, connections usually consist of a simple
electrical bus and, especially in the case of a
chain of many devices, may require the use of one or more
repeaters or
amplifiers within the chain to counteract
attenuation (the natural loss of energy in such a system).
Digital signal
A digital signal is a Signal (electrical engineering), signal that represents data as a sequence of discrete space, discrete values; at any given time it can only take on, at most, one of a finite number of values. This contrasts with an analog ...
s between devices may also travel on a simple electrical bus, in which case a bus
terminator
Terminator may refer to:
Science and technology
Genetics
* Terminator (genetics), the end of a gene for transcription
* Terminator technology, proposed methods for restricting the use of genetically modified plants by causing second generation s ...
may be needed on the last device in the chain. However, unlike analog signals, because digital signals are
discrete, they may also be electrically regenerated, but not modified, by any device in the
chain.
Types
Computer hardware
Some hardware can be attached to a computing system in a daisy chain configuration by connecting each component to another similar component, rather than directly to the computing system that uses the component. Only the last component in the chain directly connects to the computing system. For example, chaining multiple components that each have a
UART port to each other. The components must also behave cooperatively. e.g., only one seizes the communications bus at a time.
*
SCSI
Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interface ...
is an example of a digital system that is electrically a
bus
A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...
, in the case of external devices, is physically wired as a daisy chain. Since the network is electrically a bus, it must be terminated and this may be done either by plugging a terminator into the last device or selecting an option to make the device terminate internally.
*
MIDI devices are usually designed to be wired in a daisy chain. It is normal for a device to have both a THRU port and an OUT port and often both can be used for chaining. The THRU port transmits the information through with minimal delay and no alteration, while the OUT port sends a completely regenerated signal and may add, remove, or change messages, at the cost of some delay in doing so. The difference can result in the signals arriving at different times; if the chain is long enough, it will be distorted so much that the system can become unreliable or non-functional.
* Some
Serial Peripheral Interface Bus (SPI) IC products are designed with daisy chain capability.
* All
JTAG
JTAG (named after the Joint Test Action Group which codified it) is an Technical standard, industry standard for verifying designs and testing printed circuit boards after manufacture.
JTAG implements standards for on-chip instrumentation in ele ...
integrated circuits should support daisy chaining according to JTAG daisy chaining guidelines.
*
Thunderbolt (interface) also supports daisy-chained devices such as
RAID arrays and
computer monitors.
* The
Hexbus is the 10-wire bus of
Texas Instruments, used in the
TI-99/4A,
CC-40 and
TI-74.
Network topology
Any particular daisy chain forms one of two network topologies:
* Linear topology: For example, A-B-C-D-E, A-B-C-D-E & C-M-N-O (branched at C) are daisy chain.
* Ring topology: there is a loop connection back from the last device to the first. For example, A-B-C-D-E-A (loop). This is often called a "daisy chain loop".
[
Joel Konicek, Karen Little.
"Security, ID systems, and locks: the book on electronic access control"
1997.
p. 170: daisy chain loop illustration]
System access
Users can daisy chain computing sessions together. Using services such as
Telnet or
SSH, the user creates a session on a second computer via Telnet, and from the second session, Telnets to a third and so on. Another typical example is the "terminal session inside a terminal session" using
RDP
RDP may refer to:
Computing
* Ramer–Douglas–Peucker algorithm, an algorithm for polygonal simplification
* Recombination detection program, for analysing genetic recombination
* Recursive descent parser, a type of top-down parser
* Remote Des ...
. Reasons to create daisy chains include connecting to a system on a non-routed network via a gateway system, preserving sessions on the initial computer while working on a second computer, to save bandwidth or improve connectivity on an unstable network by first connecting to a better connected machine. A less wholesome purpose is camouflaging activity while engaged in
cybercrime
A cybercrime is a crime that involves a computer or a computer network.Moore, R. (2005) "Cyber crime: Investigating High-Technology Computer Crime," Cleveland, Mississippi: Anderson Publishing. The computer may have been used in committing t ...
.
References
{{Computer-bus
Electrical engineering
Installation software
Computer systems