IEEE 1394 (FireWire)
The standard provides a guaranteed theoretical bandwidth of up to 50 MB/s and allows data transfer over distances of up to 4.5 m for IEEE 1394a at 400 Mb/s and 14 m at 200 Mb/s. Depending on the set-up and the quality of the cabling, longer distances can be achieved.
In approximately 2004 the next generation FireWire called IEEE 1394b was developed, which increased the data rate up to a guaranteed bandwidth of 100 MB/s (800 Mb/s) with tests showing that 83 MB/s is possible in real world conditions. While the future roadmap for FireWire includes proposed standards with speeds of 1600 and 3200 Mb/s, at the time of writing there is no evidence that the machine vision industry will adopt them with USB 3.0 becoming the interface of choice for highspeed host based interfacing. IEEE 1394b also adds three other cabling options. CAT5 twisted pair, delivering 100 Mb/s over a distance of 100 m; Plastic Optical Fibre (POF) giving 200 Mb/s over a distance of 100 m and Glass Optical Fibre (GOF) giving 800 Mb/s over a distance of 100 metres, with tests showing that 400 m lengths are possible. For vision use, GOF represents the only viable solution for long distances due to the limited data rates of the other cabling options.
A dedicated uncompressed IEEE 1394 video standard for industrial and scientific applications has been developed by the IIDC (Instrumentation & Industrial Digital Camera Working Group) called the DCAM standard. It offers true plug and play functionality, removing the need for camera definition files and time consuming set-ups. DCAM defines a standard register map for the camera, standard resolutions and standard frame rates. To provide flexibility, the standard also includes an arbitrary format called Format 7, which provides user registers that allow new features to be added that are not defined in the DCAM standard. As most cameras include a number of of non-standard "smart features" such as time stamping, delayed read-out and partial scan, DCAM has lost its plug and play advantage with camera manufacturers providing dedicated SDK's to control the specialist features of their cameras.
FireWire remains one of the best selling digital camera interfaces for slower speed cameras in terms of units shipped per year, however, for new applications its generally being superseded by USB3 Vision and GigE Vision.
FireWire topographical models
IEEE 1394 is a bus system that can have up to 63 nodes of which 16 can be cameras. The architecture provides two communication channels, one asynchronous channel for camera register control and an isochronous, (asynchronous data transfer over a synchronous link) which uses DMA channels to deliver data with minimum or no CPU overhead. The number of DMA channels on the host PC interface defines the number of cameras that can be active at the same time and is typically 4, although some cards can support up to 8 cameras.
Cabling and locking mechanisms
One concern that vision developers have had with IEEE 1394 is the fact that the standard does not define locking connectors or robotic grade cables. However, STEMMER IMAGING offers a range of cables that meet these needs. They are available with or without locking options and robot flexibility and are fully compatible with our range of cameras and interface cards. For a more in-depth discussion of the different connector types, please refer to the cabling section.