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IEEE 1394 Tutorial


Firewire® Explained

The IEEE 1394 interface is a serial bus interface standard for high-speed communications and real-time data transfer. The interface also is known as Firewire® by Apple®, and i. LINK® by Sony®. IEEE 1394 has replaced parallel SCSI in many applications due to lower implementation costs and a simplified, more adaptable cabling system. Many modern digital camcorders and computers have included this connection for home or professional audio/video uses. IEEE 1394 makes full use of all SCSI capabilities and has high sustained data transfer rates, a feature especially important for audio and video editors. Benchmarks show that the sustained data transfer rates are higher for IEEE 1394 than for USB 2.0. However, the royalty demanded by the patent-holders and more expensive hardware needed to implement it have prevented IEEE 1394 from displacing USB in low-end mass-market computer peripherals.


Technical specifications

IEEE 1394 can connect up to 63 peripherals in a tree topology, as opposed to Parallel SCSI's Electrical bus. 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. IEEE 1394 also supports multiple hosts per bus. It is designed to support plug-and-play and hot swapping. Its six-wire cable is more flexible than most Parallel SCSI cables and 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.


Operating system support

Full support for IEEE 1394a and 1394b is available. Microsoft Windows XP supports both, but as of Service Pack 2, each device will run at S100 (100 MBs). A download is available from Microsoft which enables devices rated at S400 or S800 speeds to operate at their rated speed. Some IEEE 1394 hardware manufacturers also provide custom device drivers which replace the Microsoft OHCI host adapter driver stack, enabling S800-capable devices to run at full 800 MBs.


Standards and versions

IEEE 1394 400 (IEEE 1394-1995)

IEEE 1394 400 can transfer data between devices at 100, 200, or 400 MBs. These different transfer modes are commonly referred to as S100, S200, and S400. Cable length is limited to 4.5M (14.8 ft), although cables can be daisy chained using active repeaters or hubs often present in IEEE 1394 equipment. The S400 standard limits any configuration's maximum cable length to 72M (240ft). The 6-pin connector commonly found on desktop computers can supply the connected device with power.


Comparison to USB

Although high-speed USB 2.0 runs at a higher signaling rate (480 Mbit/s) than IEEE 1394 400, typical USB PC-hosts rarely exceed sustained transfers of 35 MB/s (280 Mbit/s). IEEE 1394 800 is substantially faster than Hi-Speed USB.


Enhancements (IEEE 1394a-2000)

An amendment IEEE 1394a was released in year 2000, which both clarified and enhanced the original specification. It added in support for asynchronous streaming, quicker bus reconfiguration, and a power saving suspend mode. 1394a also standardized the 4 pin connector already widely in use. The 4-pin version is used on many consumer devices such as camcorders, laptops, and other small IEEE 1394 devices. Though fully data compatible with 6-pin interfaces, it lacks power connectors.

IEEE 1394 800 (IEEE 1394b-2002)

IEEE 1394 800, Apple's name for the 9-pin S800 bilingual version of the IEEE 1394b standard, was introduced by Apple to allow a transfer rate of 786 MBits/s.  It is backward compatible to the slower rates and 6-pin connectors of IEEE 1394 400. However, while the IEEE 1394a and IEEE 1394b standards are compatible, IEEE 1394 800's connector is different from IEEE 1394 400's connector, making the legacy cables incompatible. A bilingual cable allows the connection of older devices to the newer port. The full IEEE 1394b specification supports data rates up to 3200 MBits/s over beta-mode or optical connections up to 100M (330ft) in length.
The Cutting Edge ~ Newest Technology

IEEE 1394 S1600 and S3200

The 1394 Trade Association announced that products will be available before the end of 2008 using the S1600 and S3200 modes which were already defined in 1394b. The devices will use the same 9-pin connectors as the existing IEEE 1394 800 and will be fully compatible with existing S400 and S800 devices. The future products are intended to compete with the forthcoming USB 3.0.

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