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| The terms shown in Figure | ||
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| Host Adapter | Links the computer’s PCI bus to the IEEE 1394 interface. To use a |
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| host adapter, computers must be PCI Rev. 2.0 compliant. |
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| HP E8491A | Links the IEEE 1394 interface to the VXI backplane. Provides the |
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| backplane’s clock and trigger resources. |
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| Interconnect |
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| Root Node | Each device (HP E8491A) on the bus is a “node.” In VXI systems, |
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| the PC is always the root node having cycle master and bus master |
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| capabilities. |
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| Branch Node | A branch node has IEEE 1394 cables connected to two or more |
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| ports. In Figure 1, VXI mainframe 1 is a branch node because of the |
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| 1394 cables connecting it to the PC (root node) and to VXI |
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| mainframe 3 on its right. |
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| Leaf Node | A leaf node has a single IEEE 1394 cable connected to it.VXI |
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| mainframes 2 and 3 are leaf nodes. |
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| Parent | A node (HP E8491A) is a parent if it is physically connected closer |
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| to the root than an adjacent node. In Figure 1, VXI mainframe 1 is a |
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| parent node because it is closer to the root than VXI mainframe 3. |
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| Child | A node (HP E8491A) is a child if it is farther from the root than an |
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| adjacent node. In Figure 1, VXI mainframe 3 is a child node |
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| because it is farther from the root than VXI mainframe 1. |
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| A node with a single IEEE 1394 cable connected to it (leaf node) is |
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| always a child (VXI mainframe 2). |
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| Hop | A hop is a IEEE 1394 cable link between nodes. There can be no |
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| more than 16 hops between any two nodes. In the diagram above, |
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| there is a maximum of three hops between nodes. The distance |
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| between any two nodes cannot exceed 72m. |
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Features of the IEEE 1394 Bus
The following features of the IEEE 1394 bus apply to all bus applications including VXI systems.
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*Up to 63 devices (including 16 HP E8491As) 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.
58 IEEE 1394 Fundamentals and Interface Overview | Chapter 4 |