FireWire

FireWire, as defined in the ubiquitous SCSI-3 standard, is also known as IEEE 1394 or as the High Performance Serial Bus. This fast and modern computer interface, known as DV or iLink when fitted on digital video (DV) cameras, replaces the older SCSI family of ports, as well as Centronics parallel ports, which can be found on earlier PC-based devices.

Unlike USB, a FireWire connection doesn’t have to involve a computer. It also handles data at multiple speeds, supports synchronous and asynchronous transfers and can use 5C copy-protection for copyright material. All of these features make it ideal for transferring digital video material. And in future, with Serial Bus Protocol 3 (SBP-3), it will be possible to connect a FireWire device such as a video camera directly to a disk drive without employing a computer.

FireWire can also be used to create a Musical Local Area Network (mLAN), as used in some Yamaha musical and audio products. When running at 200 Mbit/s this accommodates up to 100 high-quality audio channels or 256 MIDI ‘ports’ that can convey musical sequences. Support for this is provided in Mac OS X 10.3.3 or higher.

FireWire Variations

The standard IEEE 1394a interface gives a transfer rate of 12.5, 25, 50, 100, 200 or 400 Mbit/s, the ports on an original Apple G4 running at the maximum of 400 Mbit/s, corresponding to around 50 MB/s.

The newer IEEE 1394b standard, also known as FireWire 2 or GigaWire, operates at 800, 1600 or 3200 Mbit/s. Data can be sent over standard Ethernet (Cat 5) cable, plastic optical-fibre (POF) cable or 50-micron multimode fibre (MMF) glass cable. Optical cables can be used for up to 100 metres, while copper cable is limited to 412 metres.

  FireWire Products

Many FireWire devices perform the same role as a USB device (see above), although most products are specifically designed for use with high-speed data. Here are a few examples:-

Disk Drive

FireWire is ideal for connecting an external hard disk drive or an extra CD drive or DVD drive. Unfortunately, the speed performance is dependent on the equipment that’s in use. For example, older FireWire drives often contain an Ultra ATA drive together with a bridge chip for the FireWire connection. The latter sometimes run at only 12 Mbit/s, although the more recent Oxford Technology 911 bridge operates at 38 Mbit/s. Sadly, this means that the FireWire interface is often faster than the drive, although future devices will almost certainly overcome this limitation.

MIDI and Audio Adaptor

This kind of device is used by electronic music composers. One advanced model, as produced by Mark of the Unicorn, uses 24-bit processing at a sample rate of 96 kHz. It has eight main analogue audio inputs and outputs, as well as eight digital audio inputs and outputs that appear on a pair of optical connectors that are designed for connecting to an Alesis A-DAT 8-track recorder. There are further analogue circuits, as well as stereo digital inputs and outputs in the form of S/PDIF connections. In addition, it has MIDI inputs and outputs, a SMPTE timecode audio input and output, a 9-pin synchronisation input for an A-DAT machine and word clock connections for ensuring that the digital audio data is correctly timed with other digital devices.

MP3 Player

Any sound files that have been encoded in MP3 format can be downloaded via FireWire to a portable MP3 player, allowing you to carry part or all of your music collection around with you. Apple’s iPod is a very popular example of such a device.

SCSI Adaptor

This can connect an older SCSI drive to a modern machine, although you may be limited to only one such drive at a time. In addition, the speed of the connection may be limited by the bridge chip inside in the adaptor (see above).

Storage Area Network (SAN) Device

This is a special box containing multiple disk drives, often involving RAID technology, allowing several computers on a network to read and write information to the disks at high speed.

Video Adaptor

This lets you connect an analogue video source via a FireWire port. However, you can avoid the cost of such a converter by connecting the signal to the input of a standard DV camcorder instead. The DV output of the recorder can then be connected to the FireWire port on your computer: the recorder should be switched into Record mode with the Pause button enabled.

Web Camera

A suitable video camera can be connected via a FireWire port. Apple’s iSight is ideal for use with iChatAV, since it also has a built-in microphone. However, to use this kind of camera you’ll need a faster Internet connection than that provided by a dial-up modem. In conjunction with special software, such as EvoCam (Evological Software), you can use or more iSight cameras as a remote surveillance system, automatically uploading the images to a server or sending them via e-mail.

Apple Pro Speaker Adaptor

Apple Pro Speakers are designed to be connected via a special socket on older Apple G4 computers, but with this kind of adaptor you can use them with any FireWire-equipped computer. Note that this kind of adaptor only uses the FireWire port as a source of power, the audio signal being obtained from the computer’s headphone socket.

Connectors and Cables

FireWire 400 connections normally appear on a 4-way modular socket (square when viewed end-on) or a 6-way socket (rectangular, with cut-off corners to one side), as illustrated here:-

Some computers have 6-way sockets, which provide a +5-volt power supply for connected equipment. Unfortunately, others use the 4-way variety, which lacks a power feed, necessitating external power supplies for all the devices.

FireWire 800 uses a larger rectangular connector of 8 mm by 5 mm. This comes in two types: a bilingual 9-way connector conveying both IEEE 1394b and 1394a data, or a beta connector, used on devices that only support IEEE 1394b.

These different connectors are a complication, especially since small devices often have a 4-way socket. So, depending on your hardware, each FireWire device needs a cable with a 6 or 9-way plug at one end and a 9, 6 or 4-way plug at the other.

FireWire Cables

FireWire cables come in lengths of 2 feet (0.7 m), 612 feet (2 m) or 15 feet (4.5 m). The last of these corresponds to the maximum recommended length for an IEEE 1394a circuit, although you can use repeater boxes for longer distances. Fortunately, the IEE 1394b standard, including FireWire 800, lets you use cables up to 100 m in length without a repeater.

Creating a FireWire Network

In theory, a total of 63 FireWire devices can be connected to a computer, and you don’t have to worry about device IDs or terminators. In some instances, for example where a port is provided by an add-on PCI card inside your computer, this number falls to 62, although this isn’t usually a problem.

However, only 16 devices (sometimes 12) can be wired to a single daisy-chain, which means you may have to use a FireWire hub. Although each port on a computer typically provides 60 watts of power for peripheral devices, the supply from a portable is usually only adequate for one device. Fortunately, a FireWire hub should provide sufficient power at each outlet.

A total of 1,022 port buses can be bridged together to form a larger FireWire system. You can even create a network of computers by simply connecting your machines, either directly or via a hub, possibly wired to other shared devices as well. Usually, such a network employs standard TCP/IP Internet protocols, known in this context as TCP/IP over FireWire.

Connections in Detail

The connections for standard FireWire 400 ports are as follows:-

References

Help Center, Mac OS 9.1, Apple Computer Inc, 2001

MacWorld magazine (UK), IDG Communications, 2002-4

©Ray White 2004.