IEEE 1394


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 and Panasonic. It is most commonly known by the name FireWire, though other brand names exist such as i.LINK, and Lynx. Most consumer electronics manufacturers phased out IEEE 1394 from their product lines in the 2010s.
The copper cable used in its most common implementation can be up to long. Power and data is carried over this cable, allowing devices with moderate power requirements to operate without a separate power supply. FireWire is also available in Cat 5 and optical fiber versions.
The 1394 interface is comparable to USB. USB was developed subsequently and gained much greater market share. USB requires a host controller whereas IEEE 1394 is cooperatively managed by the connected devices.

History and development

FireWire is Apple's name for the IEEE 1394 High Speed Serial Bus. Its development was initiated by Apple in 1986, and developed by the IEEE P1394 Working Group, largely driven by contributions from Sony, Apple, Panasonic, and Philips, in addition to contributions made by engineers from LG Electronics, Toshiba, Hitachi, Canon, INMOS/SGS Thomson, and Texas Instruments.
IEEE 1394 is a serial bus architecture for high-speed data transfer, serial meaning that information is transferred one bit at a time. Parallel buses utilize a number of different physical connections, and as such are usually more costly and typically heavier. IEEE 1394 fully supports both isochronous and asynchronous applications.
Apple intended FireWire to be a serial replacement for the parallel SCSI bus, while providing connectivity for digital audio and video equipment. Apple's development began in the late 1980s, later presented to the IEEE, and was completed in January 1995. In 2007, IEEE 1394 was a composite of four documents: the original IEEE Std. 1394–1995, the IEEE Std. 1394a-2000 amendment, the IEEE Std. 1394b-2002 amendment, and the IEEE Std. 1394c-2006 amendment. On June 12, 2008, all these amendments as well as errata and some technical updates were incorporated into a superseding standard, IEEE Std. 1394–2008.
Apple first included onboard FireWire in some of its 1999 Macintosh models, and most Apple Macintosh computers manufactured from 2000 through 2011 included FireWire ports. However, in February 2011, Apple introduced its first Mac with Thunderbolt, which superseded FireWire. Apple released its last computers with FireWire in 2012. By 2014, Thunderbolt had become a standard feature across Apple's entire line of computers, effectively becoming the spiritual successor to FireWire in the Apple ecosystem. Apple's last Mac products with FireWire, the Thunderbolt Display and 2012 13-inch MacBook Pro, were discontinued in 2016. Apple sold a Thunderbolt to FireWire adapter, with a single FireWire 800 port, until 2023. A separate adapter was required to use it with Thunderbolt 3.
Sony's implementation of the system, i.LINK, used a smaller connector with only four signal conductors, omitting the two conductors that provide power for devices in favor of a separate power connector. This style was later added into the 1394a amendment. This port is sometimes labeled S100 or S400 to indicate speed in Mbit/s.
The system was commonly used to connect data storage devices and DV cameras, but was also popular in industrial systems for machine vision and professional audio systems. Many users preferred it over the more common USB 2.0 for its then greater effective speed and power distribution capabilities. Benchmarks show that the sustained data transfer rates are higher for FireWire than for USB 2.0, but lower than USB 3.0. Results are marked on Apple Mac OS X but more varied on Microsoft Windows.

Patent considerations

Implementation of IEEE 1394 is said to require use of 261 issued international patents held by ten corporations. Use of these patents requires licensing; use without license generally constitutes patent infringement. Companies holding IEEE 1394 IP formed a patent pool with MPEG LA, LLC as the license administrator, to whom they licensed patents. MPEG LA sublicenses these patents to providers of equipment implementing IEEE 1394. Under the typical patent pool license, a royalty of US$0.25 per unit is payable by the manufacturer upon the manufacture of each 1394 finished product; no royalties are payable by users.
The last of the patents, MY 120654 by Sony, expired on November 30, 2020., the following are patent holders of the IEEE 1394 standard, as listed in the patent pool managed by MPEG LA.
CompanyTotal patents
Sony102
Apple58
Panasonic46
Philips43
LG11
Toshiba10
Hitachi4
Canon1
Compaq1
Samsung1

A person or company may review the actual 1394 Patent Portfolio License upon request to MPEG LA. MPEG LA does not provide assurance of protection to licensees beyond its own patents. At least one formerly licensed patent is known to have been removed from the pool, and other hardware patents exist that reference IEEE 1394.
The 1394 High Performance Serial Bus Trade Association was formed to aid the marketing of IEEE 1394. Its bylaws prohibit dealing with intellectual property issues. The 1394 Trade Association operates on an individual no cost membership basis to further enhancements to 1394 standards. The Trade Association also is the library source for all 1394 documentation and standards available.

Technical specifications

FireWire can connect up to 63 peripherals in a tree or daisy-chain topology. It allows peer-to-peer device communication — such as communication between a scanner and a printer — to take place without using system memory or the CPU. FireWire also supports multiple host controllers per bus. It is designed to support plug and play and hot swapping. The copper cable it uses in its most common implementation can be up to long and is more flexible than most parallel SCSI cables. In its six-conductor or nine-conductor variations, it can supply up to 45 watts of power per port at up to 30 volts, allowing moderate-consumption devices to operate without a separate power supply.
FireWire devices implement the ISO/IEC 13213 configuration ROM model for device configuration and identification, to provide plug-and-play capability. All FireWire devices are identified by an IEEE EUI-64 unique identifier in addition to well-known codes indicating the type of device and the protocols it supports.
FireWire devices are organized at the bus in a tree topology. Each device has a unique self-ID. One of the nodes is elected root node and always has the highest ID. The self-IDs are assigned during the self-ID process, which happens after each bus reset. The order in which the self-IDs are assigned is equivalent to traversing the tree depth-first, post-order.
FireWire is capable of safely operating critical systems due to the way multiple devices interact with the bus and how the bus allocates bandwidth to the devices. FireWire is capable of both asynchronous and isochronous transfer methods at once. Isochronous data transfers are transfers for devices that require continuous, guaranteed bandwidth. To support both methods, FireWire dedicates a certain percentage to isochronous data and the rest to asynchronous data. In IEEE 1394, 80% of the bus is reserved for isochronous cycles, leaving asynchronous data with a minimum of 20% of the bus.

Encoding scheme

FireWire uses data strobe encoding. In D/S encoding, two non-return-to-zero signals are used to transmit the data with high reliability. The NRZ signal sent is fed with the clock signal through an XOR gate, creating a strobe signal. This strobe is then put through another XOR gate along with the data signal to reconstruct the clock. This in turn acts as the bus's phase-locked loop for synchronization purposes.

Arbitration

The process of the bus deciding which node gets to transmit data at what time is known as arbitration. Each arbitration round lasts about 125 microseconds. During the round, the root node sends a cycle start packet. All nodes requiring data transfer respond, with the closest node winning. After the node is finished, the remaining nodes take turns in order. This repeats until all the devices have used their portion of the 125 microseconds, with isochronous transfers having priority.

Standards and versions

The previous standards and its three published amendments are now incorporated into a superseding standard, IEEE 1394-2008. The features individually added give a good history on the development path.

FireWire 400 (IEEE 1394-1995)

The original release of IEEE 1394-1995 specified what is now known as FireWire 400. It can transfer data between devices at 100, 200, or half-duplex data rates. These different transfer modes are commonly referred to as S100, S200, and S400.
Cable length is limited to, although up to 16 cables can be daisy chained using active repeaters, e.g. external hubs or the internal hubs that are often present in FireWire equipment. The S400 standard limits any configuration's maximum cable length to. The 6-conductor connector is commonly found on desktop computers and can supply the connected device with power.
The 6-conductor powered connector, now referred to as an alpha connector, adds power output to support external devices. Typically a device can pull about 7 to 8 watts from the port; however, the voltage varies significantly from different devices. Voltage is specified as unregulated and should nominally be about 25 volts. Apple's implementation on laptops is typically related to battery power and can be as low as 9 V.