FireWire networks could get a bigger role in industrial equipment thanks to a new standard that targets real-time automation.
The IEEE 1394 standard, aka FireWire or iWire, was originally created by Apple Computer as a high-speed way of interconnecting consumer electronics inexpensively. Up to 63 devices can be connected on a 1394 network. Bus bridges will extend that number to over 60,000. 1394 defines three signaling rates: 98.304, 196.608, and 393.216 Mbit/sec. Most industrial devices that use 1394 operate at the fastest rate. The latest version of the standard, 1394b, became finalized in 2002 and expands the definition to rates of 800 and 1,200 Mbit/sec. But devices of different speeds can operate on the same 1394 bus.
Modern PCs all support FireWire, though the 1394 Trade Association reports there have been problems running it with the most recent version of Windows XP. Regardless, 1394 is a peer-to-peer network so a device other than a PC can act as a bus controller.
1394 devices can connect in multiple configurations such as star or tree patterns with daisy-chain branches. In these networks, addressing takes place dynamically so there is no need for preaddressing.
1394 can multiplex various types of digital signals onto its two twisted-pair conductors. This makes it possible to pass video, audio, and device control commands over 1394. The standard also uses a fairness arbitration approach to assure all devices get access to the bus. The protocol includes device-specific commands for widely used consumer devices such as camcorders.
One reason for the interest in 1394 as an industrial bus is its isochronous data transmission. This mechanism guarantees a certain minimum data rate as needed for time-dependent data such as video, audio, or commands for fast servosystems.
Cables carrying 1394 signals are limited to 4.5 m between devices. Industrial suppliers that field 1394 equipment say the length restriction doesn't pose a problem because motor drives, amplifiers, and cameras tend to reside close together on most applications. Special transceivers have been developed to boost the length between devices used in home-automation systems.