(APPENDIX IV) CAN COMMUNICATIONS |
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12. APPENDIX IV: CAN COMMUNICATIONS
12.1 INTRODUCTION
The CAN BUS, is an industrial bus characterized by great strength and reliability
and ensures proper communication between the devices in noisy environments.
Devices with CAN controller can be integrated into an industrial automation and
control system.
The most relevant characteristics of a control system with communication via
CAN bus are as follows:
•
It is possible to connect up to 110 devices on a single CAN network.
•
Each network can reach up to 1000 meters in length, easily
expandable (up to 2000 m) with the use of bridges or repeaters.
•
CAN baud rate of 50 kbits / s (for 1000 metres of bus: 10 ms data
update).
•
Direct access to the CAN bus from a PC via USBCan.
The CANbus can operate in environments with extreme noise and interference,
while the error checking mechanisms ensure that the connections contaminated
by noise are detected.
The CAN bus is designed so that communication will continue even if:
•
Either of the two bus cables breaks.
•
Any cable has short-circuited to ground.
•
Any wire has short-circuited to the power supply.
12.2 TOPOLOGY
The CAN network uses a bus topology, where each node has an input and an
output connection. The end nodes of the bus must have a 120Ω terminator; said
terminator is activated via a switch on each module (ON: active terminator, 1:
inactive terminator). In any case, the existing impedance between the CANH and
CANL lines should be approximately 60 Ω. For this purpose at each end of the
network a resistance value should set such that said impedance is guaranteed
from any module connected.
