HP E8491A Features of the Ieee 1394 Bus, Terms shown in -1 are defined in the following table

	The terms shown in Figure 4-1 are defined in the following table.
	Table 4-1. Definition of Terms.
Host Adapter	Links the computer’s PCI bus to the IEEE 1394 interface. To use a
	host adapter, computers must be PCI Rev. 2.0 compliant.
HP E8491A	Links the IEEE 1394 interface to the VXI backplane. Provides the
1394-to-VXI	backplane’s clock and trigger resources.
Interconnect
Root Node	Each device (HP E8491A) on the bus is a “node.” In VXI systems,
	the PC is always the root node having cycle master and bus master
	capabilities.
Branch Node	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.
Leaf Node	A leaf node has a single IEEE 1394 cable connected to it.VXI
	mainframes 2 and 3 are leaf nodes.
Parent	A node (HP E8491A) 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.
Child	A node (HP E8491A) 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).
Hop	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.

Features of the IEEE 1394 Bus

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 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