Firewire - The Specs, the connector names and comparison to USB



FireWire, the common name for the IEEE 1394 interface, was first developed by Apple in the late 1980s and early 1990s. They gave it this name, which has been widely accepted across the electronics industry. Although development started before the USB, FireWire wasn’t introduced into their computers until 1999. This interface is also known by the name i.LINK (Sony) and LYNX (Texas Instruments).


The FireWire interface provided Apple with similar serial connection capabilities as the rest of the computer industry gained from the USB. As usual, Apple didn’t follow the pack, but came up with their own, generally superior interface.


Today, FireWire connectors are found on most computers, not just Apple computers. More than anything, it has been used as a specialized connector for connecting digital video camcorders to computers, so that video can be uploaded to the computer. In the same way, it is used to connect digital video camcorders directly to data storage devices. While it is capable of being used for any other serial interface, just like the USB connection, the computer industry has not given it widespread acceptance for other applications.


FireWire Speed


Although USB is technically faster, reading speed specifications, FireWire is actually a faster communications protocol. However, the new USB 3.0 has eliminated FireWire’s speed advantage, actually being faster in head-to-head tests. The difference in communications speeds comes from the difference in communications protocols. FireWire has two data streams, compared to USB’s one.


The original FireWire is now known as FireWire 400. It provided the capability for data transfer speeds of 100, 200 or 400 Mbit/s data rates, in a half-duplex mode. Half-duplex means that data is only flowing in one direction at a time, whereas full-duplex would allow data to flow in both directions at the same time. Cable length for FireWire 400 is limited to 4.5 meters (14.8 ft.).


Since then, the FireWire specification has gone through several revisions, with the current FireWire S800T allowing 800 Mbit/s transfer rates, as well as allowing FireWire to transmit over Cat5e cables, as well as FireWire cables. An earlier FireWire 800 specification created a type B connection, which Apple refers to as a “bilingual connector.” This connector allows full-duplex communications.


FireWire Connectivity


Like USB, FireWire can be used with multiple devices. It allows a total of 63 peripherals in either a tree (using hubs) or daisy-chain topology. It can also support multiple hosts on the bus, something that USB can’t do. It can provide a maximum of 45 watts of power, per port, at up to 30 volts. This allows moderate consumption devices to be powered off of a FireWire port, without the use of a separate power supply.


Due to the two-way communications which is a normal part of the FireWire protocol, it is possible to use FireWire for peer-to-peer communications between devices, without the need for a host computer. While this is not commonly done, it makes it possible to use FireWire to have devices communicate with each other, without taking up CPU time.


An example of this would be connecting a digital camera to a printer, so that photos could be printed directly. Even though the FireWire bus may be connected to a computer, the two devices could communicate with each other, allowing printing of the photos, while the computer is involved in other tasks.


Since FireWire and USB use different communications protocols, they cannot be connected directly together, although there are adapters manufactured and available on the market. To connect the two together requires the use of an adapter card, which can convert one signal protocol to the other.


Rich Murphy