Ricoh B089 Service Manual page 802

IEEE1394 BOARD (FIREWIRE)
When the host computer powers up, it queries all the devices connected to the bus
and assigns each one an address, a process called enumeration. Here are some
general features of Firewire:
• Firewire is Plug-and-Play.
• Firewire devices are hot pluggable (they can be plugged while the system is
operating).
• 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:
• 10-bit Bus ID. Used to determine the Firewire bus where the data came from.
• 6-bit Physical ID. Used to identify the device that sent the data.
• 48-bit Storage Area. Capable of addressing 256 terabytes of information for
each node
• The Bus ID and Physical ID comprise the 16-bit Node ID. 64,000 nodes are
allowed on each system.
• Up to 16 hops are allowed (4.5 m/hop) for a total of 72 meters devices are daisy-
chained.
• Firewire allows its devices to draw power from the Firewire connection. Two
power connectors in the cable can supply power (8 to 40 V, 1.5 amp max.)
• An important element of Firewire is its support of isochronous devices.
When isochronous devices are in the isochronous mode, data streams between
the device and the host in real time with guaranteed bandwidth and no error
correction. Essentially, this means that a device like a digital camcorder can
request that the host computer allocate enough bandwidth for the camcorder to
send uncompressed video in real time to the computer. The camera can sent
data via the Firewire connection in a steady flow to the computer without
anything disrupting the process. This is one of the main reasons why 1394 has
been widely adopted by the consumer electronics industry.
B577 4-4 SM