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. Other than a full, single loop, systems which contain internal loops cannot be called daisy chains.
Daisy chains may be used for power, analog signals, digital data, or a combination thereof.

Examples

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".

The term daisy chain may refer either to large scale devices connected in series, such as a series of power strips 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 USB

Universal Serial Bus

USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....

, FireWire, and ethernet

Ethernet

Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....

 cables.

Signal transmission

For analog signal

Analog signal

An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...

s, connections usually comprise a simple electrical bus and, especially in the case of a chain of many devices, may require the use of one or more repeater

Repeater

A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...

s or amplifier

Amplifier

Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...

s within the chain to counteract attenuation

Attenuation

In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...

 (the natural loss of energy in such a system). Digital signal

Digital signal

A digital signal is a physical signal that is a representation of a sequence of discrete values , for example of an arbitrary bit stream, or of a digitized analog signal...

s between devices may also comprise a simple electrical bus, in which case a bus terminator

Electrical termination

Electrical termination of a signal involves providing a terminator at the end of a wire or cable to prevent an RF signal from being reflected back from the end, causing interference...

 may be needed on the last device in the chain. However, unlike analog signals, because digital signals are discrete

Discrete signal

A discrete signal or discrete-time signal is a time series consisting of a sequence of qualities...

, they may also be electrically regenerated, but not modified, by any device in the chain.

Types

• SCSI
  SCSI
  Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
  
   is an example of a digital system that is electrically a bus
  Computer bus
  In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
  
   but, 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
  MIDI 1.0
  There are two sides to MIDI 1.0: the hardware transport specification describing the electrical and mechanical connection, and the message format specification.- Hardware transport :...
  
   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
  Serial Peripheral Interface Bus
  The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...
  
   IC products are designed with daisy chain capability.
• All JTAG
  JTAG
  Joint Test Action Group is the common name for what was later standardized as the IEEE 1149.1 Standard Test Access Port and Boundary-Scan Architecture. It was initially devised for testing printed circuit boards using boundary scan and is still widely used for this application.Today JTAG is also...
  
   integrated circuits should support daisy chaining according to JTAG daisy chaining guidelines.
• Thunderbolt (interface) also supports daisy-chained devices such as RAID
  RAID
  RAID is a storage technology that combines multiple disk drive components into a logical unit...
  
   arrays and computer monitors.