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Firewire originally was developed by Apple Computer, Inc. as a high speed serial bus, a kind of ADB on steroids. Lots of steroids. While it was developed, many thought it was actually too fast, and some lower speed interconnect like USB would be cheaper to implement. Firewire languished. Suddenly, in 1995, a tiny connector showed up on the first DV camcorders shipped by Sony. DV was the killer app for Firewire. In late 1995, Firewire was accepted as a standard by the IEEE, henceforth called IEEE 1394. |
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What is Firewire?A lot has been written already about Firewire, therefore, this page will primarily function as a pointer to the resources on-line. One of the first and still the best paper was written by Roger Jennings, a resident of Oakland, CA, who has given up running large companies and now writes large books instead. His voluminous volumes on NT, Database Development etc. are best sellers. His famous paper "Fire on the Wire" can be found here. Many people think Firewire is DV. Roger was one of the first who realized that
Firewire is much bigger than DV. It's huge. Roger writes: "The Digital VCR
Consortium, consisting of more than 50 manufacturers of consumer electronics firms has
adopted the IEEE-1394 High Performance Serial Bus as the standard digital interface
between consumer DV products. Sony's release of
three moderately-priced DV camcorders with 1394 digital audio/video input/output and
device control is a major step in the widespread adoption of the High Performance Serial
Bus for digital audio/video interconnection. Matsushita recently joined the 1394
coalition with the Panasonic NV-DE3 DV camcorder. Other Japanese camcorder and VCR
manufacturers are certain to follow the Sony and Matsushita lead. The Digital Audio/Video Interoperability Council (DAVIC)
and Europe's Digital Video Broadcast (DVB) consortium have adopted the 1394 bus for
set-top box and other broadcast-related applications. DBS set-top box manufacturers for
the U.S. market appear poised to adopt 1394 in third-generation satellite TV
receivers." What about the wire in the Firewire?As shown in the diagram at the left, the standard Firewire cable actually consists of six wires. Data is sent via two separately-shielded twisted pair transmission lines. The two twisted pairs are crossed in each cable assembly to create a transmit-receive connection. Two more wires carry power (8 to 40 v, 1.5 a max.) to remote devices. Currently, these power lines are rarely used. The wires terminate in gameboy-style plugs, also shown at the left. Sony uses a 4 conductor cable for the connection to the DV camcorders and DVCRs. They are like the above mentioned setup, but without the power wires. They terminate in smaller, 4prong connectors. To connect a Sony DV camcorder or DVCR with a standard IEE1394 Firewire device or interface card, you need an adapter cable, 4prong on one side, 6 on the other. It simply connects the data lines while omitting the power connection. According to the standard, the IEEE 1394 "wire" is good for 400 Megabits per second over 4.5 meters. The standard cable uses 28 AWG signal pairs with 40 twist/meter. The power pair in the standard cable is 22 AWG. Longer cable runs can be achieved by using thicker cable or by lowering the bit rate. DV users, keep in mind that the signaling rate of the Sony DV camcorders is only 100 Megabit per second. Can it use longer cables? The answer is: Yes. Although way outside of the spec, several people have reported successful 100 Mbit/sec transmissions over more than 20 meters using standard cable. There are also reports of thicker cables being used to span lengths of 30 meters or more at 100 Megabit per second. If you are the adventurous type, you can try using unshielded twisted pair (UTP). Don't
notify the FCC before doing this, and if your neighbors complain about strange stuff on
their TV sets, stop the experiment. We even have received reports about someone who was
running 100 Mb/s 1394 over 50 meters of Cat-5 UTP! According to lore, he ran isochronous
video for several days without a single frame dropped due to errors. Assorted Firewire links: Adaptec embraced 1394 from the get-go. They are one of the first companies with a 1394 Firewire board shipping in volume. It's sold as the DPS Spark. They make their own chips and also have one of the best sites on the topic. Texas Instruments also is one of the Firewire pioneers. Their 1394 chipset was at the core of the world's first 1394 board, a development system sold by Skipstone. In an ironic move, Skipstone was bought by Adaptec in Spring of 1995. Skipstone President Gary A. Hoffman (now VP at Adaptec) is head of the 1394 Trade Association. They also have one of the more interesting sites on the topic. Molex - the folks who build the
connectors. Chips by Symbios
and Philips
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