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>.