Jake Bishop
Computer Architecture
Jan 31, 2001
What is Firewire?
Firewire
is a digital interface that is easy to use, scalable, and hot-swappable. Firewire was originally conceived by Apple
Computers as a way to communicate large amounts of uninterrupted digital data,
such as video. It was further
developed by the IEEE 1394 Working Group, and sponsored by Adaptec, Texas
Instruments, and Apple Computers as a universal digital communications bus
between personal computers and consumer electronics such as video camcorders
and audio equipment. Firewire works as
a digital I/O serial bus. This serial bus can be bridged to a bus(PCI) or
directly access a microprocessor.
Firewire
implements asynchronous (simple load and store) and isochronous (guaranteed uninterrupted
data transfer rate) data transfers, with transfer speeds up to 400Mbps, and
supports multiple speeds for multiple transmissions over the same wire.
According
to the standard, the IEEE 1394 "wire" is good for 400 Megabits per
second over 4.5 meters. The standard cable uses 28 AWG signal pairs with
40 twist/meter. The power pair in the standard cable is 22 AWG. This is
limited currently only by the distance of the transmission, but that length can
be increased by using a heavier shielded cable, and daisy-chaining between
devices.
The standard Firewire cable actually consists of six
wires. Data is sent via two separately-shielded twisted pair transmission
lines. The two twisted pairs are crossed in each cable assembly to create a
transmit-receive connection. Two more wires carry power (8 to 40 v, 1.5 a max.)
to remote devices. Currently, these power lines are rarely used. The wires
terminate in gameboy-style plugs.
The protocol for Firewire (IEEE 1394) was designed
into three stacked layers, as shown below.
The transaction layer handles I/O requests and responses, to
interconnect with standard parallel buses.
The link layer handles all packet transmission, as well as the control
of isochronous data channels. The
physical layer handles initializing transmissions, and translating serial
transmissions to and from the link the link layer.
Firewire developers and enthusiasts believe that
Firewire has the potential to be the next universal peripheral standard,
providing data communication between PC’s, consumer electronics, and even
appliances at transmission speeds higher than ever imagined previously.
Works
sited:
DV
and Firewire Central
www.dvcentral.com/Firewire.html
Apple
Computers
http://developer.apple.com/hardware/FireWire/More_about_Firewire.html
IEEE
1394 Technology Association
http://www.1394ta.org/Technology
Adaptec
http://www.adaptec.com/worldwide/product/prodtechindex.html?cat=/Technology/FireWire-1394