903-0628-00 Rev. 1
Model 903-HD User's Guide – FMB-X-2.5
Focal Technologies Corp.
Page 4-25
4.3.8 CANBUS Plug-In (AIB-CANBUS)
Card P/N 903-0297-00
The CAN bus interface AIB plug-in (AIB-CANBUS), as shown in the figure below, provides transparent
extension of CAN 2.0A and 2.0B over the fiber optic multiplexer system. Each AIB card acts as a node on the
local CAN bus, handling media access and packet 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 bridge are regenerated as CAN format packets at the other end
and placed on the local bus.
This CAN bus bridge 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
s 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
s/km of latency in each direction.
Figure 4-17: AIB-CANBUS Plug-In Module (Top View)
The optical bridge maintains the full 1 Mbps maximum data rate of CAN when used with the Model
914, Model 907, or in the high speed data slot of a GLINK-based Model 903 system. In a low speed
data slot on a GLINK-based Model 903 system, the optical link supports up to 250 kbps CAN traffic.
The 2.5G Model 903 systems (with FMB-X-2.5) support the full 1 Mbps rate of the AIB-CANBUS in any
data slot.
Maximum sustained CAN throughput is typically limited by the bus master, not the AIB-CANBUS cards.
Messages 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 link. The maximum unidirectional throughput is 75% at 1 Mbps and 100% at all other
speeds.
Содержание Focal 903
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