Daisy chain (electrical engineering)

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.^[1] 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".^[2][3][4]

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, FireWire, and ethernet cables.

Signal transmission

For analog signals, 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 repeaters or amplifiers within the chain to counteract attenuation (the natural loss of energy in such a system). Digital signals between devices may also comprise a simple electrical bus, in which case a bus terminator 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

A series of devices connected in a daisy-chain layout

• SCSI is an example of a digital system that is electrically a bus 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 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 IC products are designed with daisy chain capability.
• All JTAG integrated circuits should support daisy chaining according to JTAG daisy chaining guidelines.^[5]
• Thunderbolt (interface) also supports daisy-chained devices such as RAID arrays and computer monitors.^[6]

References

1. ^ Electrical Engineering Glossary Definition for Daisy Chain
2. ^ "New device network topologies - Daisy-chain and daisy-chain with loop" [1]
3. ^ IR3508Z data sheet: "The last phase IC is connected back to ... the control IC to complete the daisy chain loop." [2]
4. ^ Joel Konicek, Karen Little. "Security, ID systems, and locks: the book on electronic access control" 1997. p. 170: daisy chain loop illustration. [3]
5. ^ ViaTAP user's manual, chapter Design guidelines for use with ViaTAP
6. ^ Intel - Thunderbolt I/O technology