CAN protocol information

• CAN control area network
• Introduced by "Robert Bosch"
• It has 3 layers of OSI model:
• Physical layer (CAN Transceiver SN65HVD233)
• Data link layer (CAN Controller MCP2515)
• Application layer (Higher level protocols are implemented

Specifications:

ISO 11898

Specification is related to only following two layers

1. Physical layer
2. Data link layer

Physical connection:

2 wire interface

uC <---SPI 4---> CAN controller <---Tx & Rx ---> CAN Transceiver <--CANH & CANL

two 120ohm termination resistors are connected on the basis of transmission line theory.

CAN packet description:

• Standard

SOF(1) + ID(11) + RTR(1) + IDE(1) + RB0(1) + DLC(4) + DataFrame(8*n where 0<=n<=8) +  CRC(15) + CRCdel(1) + ACK slot(1) + ACKdel(1) + EOF(7) + IFS(3)

• Extended

SOF(1) + ID(11) + SRR(1) + IDE(1) + ID(18) + RTR(1) + RB1(1) + RB0(1) + DLC(4) + DataFrame(8*n where 0<=n<=8) +  CRC(15) + CRCdel(1) + ACK slot(1) + ACKdel(1) + EOF(7) + IFS(3)

Dominant bit = 0 logic

Recessive bit = 1 logic

Bit stuffing - if there are more than 5 consecutive dominant bits then bit stuffing mechanism is used to send a recessive bit so as to maintain the synchronization

CAN frame types:

1. standard
2. extended
3. remote request
4. errror (active & passive)
• CRC error
• acknowledgement error
• form error
• bit error
• stuff error
5. overload

CANOpen

Its a application layer protocol

1. Communication profile (CiA DS-301): The communication profile provides the means to configure devices and communication data and defines how data is communicated between devices.
2. Device profile (CiA DSP-401): 

Device profiles add device-specific behavior for (classes of) devices (e.g. digital I/O, analog I/O,  motion controllers, encoders, etc.)