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| When the host computer powers up, it queries all of the devices connected
to the bus and assigns each one an address, a process called enumeration.
FireWire is plug-and-play, so if a new FireWire device is connected to a
computer, the operating system auto-detects it and asks for the driver disk. If
the device has already been installed, the computer activates it and starts
talking to it. FireWire devices are hot pluggable, which means they can be
connected and disconnected at any time, even with the power on. |
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FireWire uses 64-bit fixed addressing, based on the IEEE 1212 standard.
There are three parts to each packet of information sent by a device over
FireWire:
A 10-bit bus ID that is used to determine which FireWire bus the data came from
A 6-bit physical ID that identifies which device on the bus sent the data
A 48-bit storage area that is capable of addressing 256 terabytes of
information for each node! |
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| The bus ID and physical ID together comprise the 16-bit node ID, which
allows for 64,000 nodes on a system. Individual FireWire cables can run as long
as 4.5 meters. Data can be sent through up to 16 hops for a total maximum
distance of 72 meters. Hops occur when devices are daisy-chained together. Look
at the example below. The camcorder is connected to the external hard drive
connected to Computer A. Computer A is connected to Computer B, which in turn
is connected to Computer C. It takes four hops for Computer C to access the
camera. |
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