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Host Adapter
HP E8491B
1394-to-VXI
Interconnect
Root Node
Branch Node
Leaf Node
Parent
Child
Hop
Features of the
IEEE 1394 Bus
58 IEEE 1394 Fundamentals and Interface Overview
The terms shown in Figure 4-1 are defined in the following table.
Table 4-1. Definition of Terms.
Links the computer's PCI bus to the IEEE 1394 interface. To use a
host adapter, computers must be PCI Rev. 2.0 compliant.
Links the IEEE 1394 interface to the VXI backplane. Provides the
backplane's clock and trigger resources.
Each device (HP E8491B) on the bus is a "node." In VXI systems,
the PC is always the root node having cycle master and bus master
capabilities.
A branch node has IEEE 1394 cables connected to two or more
ports. In Figure 1, VXI mainframe 1 is a branch node because of the
1394 cables connecting it to the PC (root node) and to VXI
mainframe 3 on its right.
A leaf node has a single IEEE 1394 cable connected to it.VXI
mainframes 2 and 3 are leaf nodes.
A node (HP E8491B) is a parent if it is physically connected closer
to the root than an adjacent node. In Figure 1, VXI mainframe 1 is a
parent node because it is closer to the root than VXI mainframe 3.
A node (HP E8491B) is a child if it is farther from the root than an
adjacent node. In Figure 1, VXI mainframe 3 is a child node
because it is farther from the root than VXI mainframe 1.
A node with a single IEEE 1394 cable connected to it (leaf node) is
always a child (VXI mainframe 2).
A hop is a IEEE 1394 cable link between nodes. There can be no
more than 16 hops between any two nodes. In the diagram above,
there is a maximum of three hops between nodes. The distance
between any two nodes cannot exceed 72m.
The following features of the IEEE 1394 bus apply to all bus applications
including VXI systems.
* Daisy-chain or branching configurations are allowed. There can be no
closed loops (i.e. more than one connection between any two devices).
* Up to 63 devices (including 16 HP E8491Bs) are allowed per bus segment.
One host adapter represents one bus segment.
* There is a maximum of 16 hops between any two devices. The bus cable
length cannot exceed 72 meters between any two devices.
* Live/hot connections. A VXI mainframe anywhere in the configuration
can be turned on/off without affecting the other mainframes. The IEEE 1394
bus automatically reconfigures itself any time a VXI mainframe (or other
device) is added or removed. It is best to do this however, if there are no
data transactions taking place elsewhere in the system.
Chapter 4
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