Daisy chain (electrical engineering)

For connecting computers, seeDaisy chain (network topology).For other uses, seeDaisy chain (disambiguation).

A graphic representation of a daisy chain

Adaisy garland,a chain of daisy flowers

A series of devices connected in a daisy chain layout

In electrical and electronic engineering, adaisy chainis a wiring scheme in which multiple devices are wired together in sequence or in a ring,similar to agarland of daisy flowers.Daisy chains may be used for power, analog signals, digital data, or a combination thereof.

The termdaisy chainmay refer either to large scale devices connected in series, such as a series ofpower stripsplugged 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 onUniversal Serial Bus(USB),FireWire,ThunderboltandEthernetcables.

Signal transmission

See also:Passthrough (electronics)

Foranalog signals,connections usually consist of a simpleelectrical busand, especially in the case of achain of many devices,may require the use of one or morerepeatersoramplifierswithin the chain to counteractattenuation(the natural loss of energy in such a system).Digital signalsbetween devices may also travel on a simple electrical bus, in which case a busterminatormay be needed on the last device in the chain. However, unlike analog signals, because digital signals arediscrete,they may also be electrically regenerated, but not modified, by any device in thechain.

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 aUARTport to each other. The components must also behave cooperatively. e.g., only one seizes the communications bus at a time.

• SCSIis an example of a digital system that is electrically abus,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.
• MIDIdevices 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.
• SomeSerial Peripheral Interface Bus(SPI) IC products are designed with daisy chain capability.
• AllJTAGintegrated circuits should support daisy chaining according to JTAG daisy chaining guidelines.
• Thunderbolt (interface)also supports daisy-chained devices such asRAIDarrays andcomputer monitors.
• DisplayPort1.2 and higher features Multi-Stream Transport (MST) mode. In this mode, multiple screens can be connected either using a hub or as a daisy chain.
• TheHexbusis the 10-wire bus ofTexas Instruments,used in theTI-99/4A,CC-40andTI-74.

Network topology

Main article:Network topology § Daisy chain

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".

System access

See also:Jump server

Users can daisy chain computing sessions together. Using services such asTelnetorSSH,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" usingRemote Desktop Protocol.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. Another reason for creating a daisy chain is to camouflage activity while engaged incybercrime.