Page 110 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes

Create a connection between two multimedia devices and exchange some data
using data cable.

6.2.6 fireWire
FireWire is Apple Computer’s version of a standard, IEEE 1394, High Performance Serial Bus,
for connecting devices to your personal computer. FireWire provides a single plug-and-socket
connection on which up to 63 devices can be attached with data transfer speeds up to 400 Mbps
(megabits per second). The standard describes a serial bus or pathway between one or more
peripheral devices and your computer’s microprocessor. Many peripheral devices now come
equipped to meet IEEE 1394. FireWire and other IEEE 1394 implementations provide:
• A simple common plug-in serial connector on the back of your computer and on many
different types of peripheral devices.
• A thin serial cable rather than the thicker parallel cable you now use to your printer.
• A very high-speed rate of data transfer that will accommodate multimedia applications
(100 and 200 megabits per second today; with much higher rates later).
• Hot-plug and plug and play capability without disrupting your computer.
• The ability to chain devices together in a number of different ways without terminators or
complicated set-up requirements.
In time, IEEE 1394 implementations are expected to replace and consolidate today’s serial and
parallel interfaces, including Centronicsparallel, RS-232C and SCSI. The first products to be
introduced with FireWire include digital cameras, digital video disks (DVDs), digital video tapes,
digital camcorders, and music systems. Since IEEE 1394 is a peer-to-peer interface, one camcorder
can dub to another without being plugged into a computer. With a computer equipped with the
socket and bus capability, any device (e.g., a video camera) can be plugged in while the computer
is running.

How it works?
There are two levels of interface in IEEE 1394, one for the backplane bus within the computer
and another for the point-to-point interface between device and computer on the serial cable. A
simple bridge connects the two environments. The backplane bus supports 12.5, 25 or 50 megabits
per second data transfer. The cable interface supports 100, 200 or 400 megabits per second. Each
of these interfaces can handle any of the possible data rates and change from one to another as
needed.
The serial bus functions as though devices were in slots within the computer sharing a common
memory space. A 64-bit device address allows a great deal of flexibility in configuring devices in
chains and trees from a single socket.
The IEEE 1394 provides two types of data transfer: asynchronous and isochronous. Asynchronous
is for traditional load-and-store applications where data transfer can be initiated and an application
interrupted as a given length of data arrives in a buffer. Isochronous data transfer ensures that
data flows at a pre-set rate so that an application can handle it in a timed way. For multimedia
applications, this kind of data transfer reduces the need for buffering and helps ensure a continuous
presentation for the viewer.

The 1394 standard requires that a device be within 4.5 metres of the bus socket. Up to 16 devices
can be connected in a single chain, each with the 4.5 metre maximum (before signal attenuation
begins to occur) so theoretically you could have a device as far away as 72 metres from the
computer.

104 LoveLy professionaL University