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IEEE-1394 FireWire
By Stephen Bucaro
IEEE 1394 FireWire is a serial bus designed by Apple Computer as a replacement
for legacy interfaces like serial ports, parallel ports, and SCSI. Firewire competes
with USB, and the two standards have switched back-and-forth as to which one has
the highest speed and the most features. Both support plug-and-play, hot-swapping,
daisy-chaining, and using hubs to support more devices.
Because Apple and other patent holders demanded royalty payments of $0.25 per
system, implementation of FireWire dragged behind that of USB. Texas Instruments
developed its own version and named it Lynx. Sony developed its own version
and named it i.Link. Sony's version uses only the four signal pins, omitting
the two pins which provide power to the device because of a separate power connector
on Sony's i.Link products.
IEEE 1394a
Apple eventually dropped its demand for royalty payments by FireWire implementers
and the IEEE 1394a amendment was released which clarified and added some technical
advancements to the original specification. It standardized the 4-pin and 6-pin
connectors made all the Firewire versions compatible.
4-pin 6-pin and 9-pin Firewire Connectors
FireWire 400
The original FireWire (IEEE 1394) and the IEEE 1394a amendment are often referred
to as FireWire 400 because its fastest data rate is 400 Mbit/s. FireWire 400 can
transfer data between devices at 100, 200, or 400 Mbit/s data rates. The 6-pin
connector can supply the connected device with power. Typically a device can pull
about 7 to 8 watts from the port.
FireWire can connect up to 63 peripherals in a tree topology. It allows peer-to-peer
device communication to take place without using the system CPU. It supports
plug-and-play and hot swapping. It can be used with cables up to 15 feet (4.5m) long.
FireWire 800 (IEEE 1394b)
The newer IEEE 1394b specification is often referred to as FireWire 800 because its
fastest data rate is 800 Mbit/s. It uses a 9-pin connector which allows continuous dual
simplex communication. With this scheme two pairs of wires are used to continuously
transmit data in each direction. It is backwards compatibile with the slower rates
and of FireWire 400, but you need a 9-pin to 6-pin adapter.
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