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CAN protocol (Part-II):Standard CAN Frame Format fields

the CAN frame structure is: SOF:Start of Frame bit. It marks start of message. It is used to synchronize nodes on the CAN bus. Identifier:It is 11 bit (binary) in size. It establishes priority of message. Lower the value, higher is the priority. RTR:It stands for Remote Transmission Request bit. This field is dominant when node requires information from another remote node. All the nodes receive request and all the nodes receive reply. Specific node processes the request based on identifier and transmits the reply. IDE: Stands for Identifier Extension bit. It indicates standard CAN frame is being transmitted with no extension. r0:It is reserved for future use DLC:Stands for Data length code. It is 4 bits in size. It indicates number of bytes to be transmitted over the CAN bus. Data:It contains upto 64 bits of application data. CRC:It is used for error detection. It is 16 bits in size. It holds checksum for application data preceding to it. ACK:It is 2 bits in size. It contains first bit as ack bit and second bit as delimiter. Each node uses this to show integrity of its data. Node receiving correct message overwrites this bit in original received message with dominate bit as mentioned above to indicate error free message has been transmitted. The node receiving erroneous message leaves this bit as recessive. Moreover it discards the message and hence prompts the sending node to re-transmit the message after re-arbitration process. EOF:Stands for End of Frame. It is 7 bits in size. It marks end of CAN frame or message.