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903-0623-00 Rev. A
Model 903 User's Guide, FMB-X-2.5 Version
5.6.7 CANBUS Plug-In (AIB-CANBUS)
Card P/N 903-0297-00
The CAN bus interface AIB plug-in (AIB-CANBUS), as shown in Figure 5.6-10, provides extension of a
CAN 2.0A and CAN 2.0B bus over the fiber optic multiplexer system. Each AIB-CANBUS card acts as a
node on the local CAN bus, handling media access and packet/message acknowledgements. The AIB
cards at either end of the multiplexer system are connected through the fiber optic link as a bridge
between two separate CAN bus networks. Packets relayed through the optical link bridge are regenerated
as CAN format packets/messages at the other end and placed on the local bus.
This CAN bus "Bridge Mode" configuration is particularly well suited to sensor networks where all of the
sensors are at one end of the system, e.g. an ROV, and the bus master controller, typically a PC, is at the
opposite end. Due to the latency inherent in the optical bridge – typically 200 µs at 1 Mbps and 1 ms at
125 kbps – this link may not be suitable for more complex CAN bus configurations or systems requiring
fast responses, such as TTCAN. The optical fiber itself adds 5 µs/km of latency in each direction.
Figure 5.6-10: AIB-CANBUS Plug-In Module (Top View)
The maximum sustained packet throughput is typically limited by the bus master, not the AIB-CANBUS
cards. Packets are transmitted through the optical link in a proprietary frame supported by 32-bit CRC to
ensure data reliability. Time-outs in applications or higher layer protocols may need to be adjusted to
account for the latency through the fiber optic system.
Focal Technologies Corp.
Page 5-34
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