How to use FireWire for innovative new designs without distance constraints

Editor's note: The following paper by Les Baxter was first posted on IEEE 1394 Trade Association's web site under the title "IEEE 1394 ideal for long-haul automotive, consumer, industrial, security, and PC applications." The article is reproduced here in full with additional information specific to industrial applications, provided by IEEE 1394 Trade Association.

Since 1995, FireWire has been a proven and popular interface for short haul audio and video transfer in PCs, storage products, and consumer electronics. To date over 1 billion ports have shipped. Now the 1394b version of FireWire (known as Beta mode), which runs at up to 3,200 megabits per second, is becoming an interface of choice for innovative and advanced long-haul applications. Since the publication of the 1394 Copper Automotive Specification in 2008, there has been significant interest in FireWire for automotive applications as well.

It's a common misconception that IEEE 1394 links are limited to 4.5 m in length. This perception is no doubt caused by the statement found in the IEEE 1394 standard that all three types of cables (4-, 6-, and 9-pin) have "a suggested maximum length of 4.5 m." The 1394 standard goes on to point out that longer length cables are possible, but this has been largely overlooked and misunderstood. Additionally, IEEE 1394-2008 contains several clauses that specify long-haul media, which can support much longer distances.

The diagram in Figure 1 illustrates a typical IEEE 1394 network with standard cables of 4.5-m lengths, which can support up to 63 nodes.

Figure 1: Typical 1394 network

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There are two ways of extending the distance of a 1394 link--either use a lower-loss cable, or use one of several longer-distance media (UTP, coax, or fiber). This article will consider these methods and give additional details on automotive applications. [Specifics about industrial applications can be found in the sidebars in this article. --editor. ]

Figure 2 shows the same network as Figure 1 except that the network is divided into two clusters of nodes. A pair of repeaters and a long haul link is used to connect the two clusters.

Figure 2: 1394 network with repeaters

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Instead of using repeaters, it is also possible to design Nodes 4 and 5 with long haul ports so that they can be directly connected. This is illustrated in Figure 3.

Figure 3: 1394 network with long haul ports

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