Firewire.

Here at Datlabs our technicians are often asked “what is Firewire and how is it used to connect devices and facilitate the interchange of data with my computer?”  The following basic description will hopefully clarify what is meant by Firewire and provide a basic understanding of the associated signalling principles involved.

Serial Data Bus.

The term serial data communication or signalling is the process of sending and receiving data one bit at a time, sequentially over a cable and/or connection between two or more computer devices. There are a number of standards that describe the signalling protocols and physical interconnects that can be implemented to ensure a reliable exchange of data takes place between communicating devices. Firewire developed by Apple is one such signalling interconnect implementation. Firewire is high performance serial data bus application for transferring information between digital devices, especially audio and video equipment. Firewire is also known as IEEE 1394.

The Firewire basic design implementation imperatives are as follows:

• Lots of interconnected devices.
• Ease of use
• Hot-pluggable ability
• Provision of power through the cable
• Plug-and-play performance
• Low cabling cost
• Low implementation cost

The FireWire specification includes data transfer interchange at speeds of up to 3.2 Gbps over specifically manufactured FireWire cables. The Firewire bus supports addressing structures for 63 interconnected devices. Firewire is available for Windows or Mac operating systems but is mainly and exclusively used for Mac.

FireWire uses Data Strobe encoding,  in which two non-return zero signals are sent with a clock reference to create a strobe. This means the clock signal can be reconstructed from its phase relationship with the data signal and a phase locked loop created to synchronize signals at either end of the data bus.

Firewire Connection.

When a Firewire enabled computer boots up it will interrogate all of the devices connected to the serial Firewire bus and then assign each responsive device a unique address. This initialisation process is called enumeration.

If you connect a new FireWire device to your computer, the operating system auto-detects the device and asks for its driver to be installed. If you’ve already installed the device, the computer activates it and starts talking to it. FireWire devices are hot pluggable, which means they can be connected and disconnected at any time, even with the power on. To provide the plug and play capability the FireWire devices implement the configuration ROM” model for device configuration and identification.

All FireWire devices are identified by an IEEE unique identifier in addition to well-known codes indicating the type of device and the protocols it supports.

FireWire and USB

FireWire is intended for use with media processing and is a peer-to-peer protocol application which means two FireWire devices can interchange data directly without a central processor such as a host PC. USB requires a host or central processor.

FireWire devices can be powered or unpowered. FireWire allows devices to draw their power from their connection. Two power conductors in the cable can supply power (8 to 30 volts, 1.5 amps maximum) from the computer to an unpowered device.

FireWire cable pin out.

Some smaller FireWire-enabled devices use 4-pin connectors to save space, omitting the two pins used to supply power. FireWire 800 cables use a 9-pin configuration. Six of those pins are the same as the six pins in the 1394a connector. Two of the added pins provide a “grounded shield” to protect the other wires from interference, and the third added pin does nothing at this time.

Because FireWire 800 is backward-compatible with FireWire 400, there are a variety of adapters available to facilitate the combination of both standards on the same bus. There are also two types of FireWire 800 ports available: a “bilingual” port accommodates both FireWire standards, while a b-only port accepts only a FireWire 800 connector.

Firewire 64 bit addressing.

FireWire uses 64-bit fixed addressing as in IEE1212 with three parts to each packet of information sent by a device over FireWire:

• 0-bit bus ID used to identify the FireWire bus.
• 6-bit physical identity of the device on the bus.
• 48-bit identity of the storage area within the device.

Firewire and Media applications.

FireWire supports isochronous mode in which data streams between a device and its host in real-time with guaranteed bandwidth and no error correction. This means that a device such as a digital camcorder can request that the host computer allocate enough bandwidth for the camcorder to send uncompressed video in real-time to the computer. When the computer-to-camera FireWire connection enters isochronous mode, the camera can send the video in a steady flow to the computer without disruption.

With the right software, the computer can download video data automatically and with perfect digital clarity. Since the content is digital from start to finish, there is no loss of quality as the editor works on successive generations.

Require more information or have a problem with your Firewire connected devices you will find more information and help via our Datlabs data recovery web site.