Contemporary Control Systems AI Active Hubs - Manual (Page 36)

TD675100-0M
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Appendices
Appendix A — Permissible Segment Lengths
A segment is defined as any portion of the complete ARCNET
cabling system isolated by one or more hub ports. On a hubless
or bus system, the complete ARCNET cabling system consists
of only one segment with several nodes; however, a system with
hubs has potentially many segments. An ARCNET node is
defined as a device with an active ARCNET controller chip
requiring an ARCNET device address. Active and passive hubs
do not utilize ARCNET addresses and, therefore, are not nodes.
Each segment generally supports one or more nodes, but in the
case of hub-to-hub connections there is the possibility that no
node exists on that segment.
The permissible cable length of a segment depends upon the
transceiver used and the type of cable installed. Table A-1
provides guidance on determining the constraints on cabling
distances as well as the number of nodes allowed per bus
segment.
The maximum segment distances are based upon nominal cable
attenuation figures and worst case transceiver power budgets.
Assumptions are noted.
When approaching the maximum limits, a link loss budget
calculation is recommended.
When calculating the maximum number of nodes (except
EIA-485 networks) on a bus segment, do not count the hub
ports that terminate the bus segment as nodes.
However, do consider the maximum length of the bus segment
to include the cable attached to the hub ports.
Several bus transceivers require a minimum distance between
nodes. Adhere to this minimum since unreliable operation can
occur.