Contemporary Research TD960801-0MC - Manual (Page 5)

TD960801-0MC
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Introduction
1.1 Description
The EXTEND-A-BUS for DeviceNet series of fieldbus
extenders enable the geographic expansion of CAN-based
device networks such as DeviceNet by linking individual
DeviceNet subnets together into a single larger network.
The medium arbitration method used by DeviceNet is intolerant
of excessive signal delay. Since cable length introduces delay,
DeviceNet networks tend to be distance limited. Repeaters are
ineffective in extending distances since they introduce additional
delay. On the other hand, fieldbus extenders like EXTEND-A-
BUS solve the problem by segmenting a single DeviceNet
network into manageable subnets.
EXTEND-A-BUS interconnects two physically separated but
similar networks using a different interconnecting medium.
Thus, a pair is required to interconnect two networks (or
subnets) the way two modems are used on leased phone lines.
Utilizing ARCNET as the high-speed deterministic
interconnecting medium, the EXTEND-A-BUS captures
DeviceNet traffic and replicates it to the receiving device. The
receiving device removes DeviceNet data and rebroadcasts the
data to its attached DeviceNet subnet. EXTEND-A-BUS does
not filter out DeviceNet identifiers or MAC addresses, so
DeviceNet messages are rebroadcast unmodified.
Application Information
Each EXTEND-A-BUS creates a DeviceNet subnet and a
minimum of two EXTEND-A-BUSes is required to establish a
network. The data rate on each subnet can be different from the
other subnets. DeviceNet identifiers or MAC ID checks are
replicated on all subnets. EXTEND-A-BUS pairs are best
viewed as an extension cord. Each EXTEND-A-BUS does not
consume a permanent MAC ID and, therefore, is transparent to
the network.