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Jonathan MeedAlexander Basil
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What is CAN (Controller Area Network)
• CAN is a multi-master serial bus
• Developed by Bosch for automotive applications in early
1980s
o Released publicly in 1986
o Became ISO standard in 1993
o Is now required in all cars in the USA
• Used for connecting multiple separate electronic
systems
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Figure 1 - Typical CAN implementation in a car [1]
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• Solar car
• Plane
• Heavy machinery
• Boats
All the places CAN can go
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What CAN looks like
Figure 3 - RS-435 Wire Specification [3]
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Low-Voltage Differential Signaling
Figure 2 - Diagram of LVDS [2]
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U CAN 2
• CAN implementation often requires additional hardware to generate LVDS
MCP2551
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Bus Idle
Inter-missio
n
SOF
EOF
AddressField
ControlField
DataField
CRCField
ACKField
Stack Frame Message
Figure 4. CAN Message bit partitioning.
Bus Idle
Inter-missio
n
for CAN 2.0A
SOF
EOF
AddressField
ControlField
DataField
CRCField
ACKField
• Start of frame (low bit)• Address (arbitration)• Control (data length, reserved bits)• Data• Cyclic Redundancy Check (error checking)• Acknowledge• End of frame• Intermission (time between frames)
1 bit 12 bits 6 bits 0-8 bytes 16 bits 2 bits 7 bits
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Message Arbitration (same as I2C)• Message includes 11-bit target address and a remote
transmission bito Lower target address value = higher priority
• Node transmits the target address bit-by-bit and receives other transmitted addresseso If it transmits a 1 and receives a 0, it loses arbitration
Figure 5 - Arbitration example. [4]
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Pros and Cons
• Proso Long transmission distance and low weighto Multiple masters with arbitrationo Great for inter-board communicationo The bus is not clocked (but requires each device on
the bus to run at the same clock speed)
• Conso Complex for single board or single device
communications I2C and SPI are more suited for this environment
o Higher cost – overhead bits and additional hardware
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Questions
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References
[1] Cook, Jeff, and Jim Freudenberg. "Controller Area Network
(CAN)." (2008): Web.
<http://www.eecs.umich.edu/courses/eecs461/doc/CAN_notes.pdf>.
[2] "Low-voltage differential signaling." Wikipedia. N.p.. Web. 21 Feb 2013.
<http://en.wikipedia.org/wiki/Low-voltage_differential_signaling>.
[3] Kugelstadt, Thomas. "Isolated CAN Transceiver Assures Robust Fieldbus Design."
ECN. Texas Instruments. Web. 21 Feb 2013.
<http://www.ecnmag.com/articles/2009/10/isolated-can-transceiver-assures-robust
-fieldbus-design>.
[4] Bitwise arbitration in CAN networks. TechnologyUK. Web.
<http://www.technologyuk.net/telecommunications/industrial_networks/can.
shtml>.