Specifications

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IEEE 1394
The High-Speed Multimedia Solution
IEEE 1394 is a high-performance serial bus designed for high
speed audio, video and data transfer applications. First introduced
by Apple Computer as “Firewire" in 1986, the standard is now
overseen by the Institute of Electrical and Electronics Engineers
(IEEE). This same standard is also referred to as “i.LINK" by Sony
Corporation which has trademarked that name.
Unlike the other wired busses described so far, IEEE 1394 is
unique in that it does not require a PC in order to function. For
example, IEEE 1394 can be used to send a picture directly from
a digital camera to a printer, or to transfer a file between two
digital video cameras. Another outstanding feature is that IEEE
1394 does not require that digital data be converted to analog.
Thus, provided that a network is comprised of exclusively digital
devices, using IEEE 1394 can considerably improve and maintain
signal integrity--even over multiple transfers of the same data.
Other advantageous IEEE 1394 features are Plug and Play and
Hot Swap capability, and the very small cable size that is ideal for
portable devices.
The first IEEE 1394 standard was designed for PC backplanes
and supported data rates of up to 50 Mbits/sec. IEEE 1394a
was approved in 2000, and supports speeds of 100 Mbits/sec,
200 Mbits/sec and 400 Mbits/sec. 1394a, which was designed
to use a cable interface, also provides improved traffic control
and added power management features. To increase speeds
even further, a new specification, IEEE 1394b, is scheduled to be
released in late 2001. The new standard is supposed to increase
IEEE 1394 bandwidth as high as 3.2 Gbits/sec.
The IEEE 1394 System
IEEE 1394 systems can connect up to 63 devices together via a
single bus connection which may or may not include a computer.
They can be connected in either a star or tree pattern, and multiple
devices can be daisy chained off any branch. Addressing for
these devices is done dynamically each time the system is powered
up, or when a device is added or removed from the network. For
even larger networks, multiple 1394 busses (up to 1,203 busses)
can be bridged together.
Both asynchronous (see page 25) and isochronous (see page
28) communication are supported under IEEE 1394.
Asynchronous communication is used for applications such as
writing data to disk, and employs the extensive error-checking
necessary to safeguard signal integrity. However, such error
checking requires a delay that makes asynchronous
communication impractical for time sensitive applications such
as streaming video. Isochronous transfers, which guarantee a
steady transfer rate but do not provide any error checking, are
used for such applications. The IEEE 1394 bus reserves space
for both types of transfer to occur in the same network, at the
same time if necessary. The IEEE 1394 network can also support
multiple devices operating at different data rates simultaneously.
IEEE 1394 Cabling
The IEEE 1394 standard includes two cable specifications. The
difference between the two is that the 6-pin connector includes
power and ground pins, allowing one 1394 device to provide
power (up to 60 watts) to others in the network. The 4-pin
connector lacks these power pins, and thus 4-pin devices must
provide their own power. The advantage to the 4-pin connector
is size--the 4-pin (at 5mm x 3mm) is considerably smaller than
the 6-pin (at 10mm x 5mm), and thus better suited for portable
applications. The maximum cable length for high speed
applications (greater than 200 Mbits/sec) is 4.5 meters. However,
at slower speeds, cables up to 14 meters long can be used.
Multiple devices can also be daisy-chained using repeaters to
extend communication distance.
6-pin
port
4-pin
ports
6-pin
connector
4-pin
connector
Power conductors (8 to 30 VDC, 1.5A)
6-pin connector only
Two independently shielded twisted wire
pairs for transmit and receive connections.
(4-pin and 6-pin)
External cable shielding
(IEEE 1394 4-pin and 6-pin connectors)
IEEE 1394 for Data Communication
IEEE 1394 has become the standard for high-speed video
applications. In fact, typical video controls such as play and
rewind have been written into the specifications. 1394 support
is included in Windows 98/Me/2000, making it a good solution
for various high-bandwidth PC-based applications such as data
transfers to external hard disks or video editing. It shares many
of the same features as USB (see page 22), though it is
significantly faster than USB 1.1. USB 2.0 comes close to matching
speed, however most people find the busses complimentary. USB
is a more general standard geared towards desktop peripherals,
and it requires a computer. IEEE 1394 has targeted the multimedia
audio/video market, and it also provides the advantage of allowing
compliant devices to communicate without a PC.
IEEE 1394