Can Protocol Interview Questions and Answers

Answer: 1. CAN is a multi-master broadcast serial bus standard for connecting electronic control unit (ECUs). 2. Controller–area network (CAN or CAN-bus) is a vehicle bus standard designed to allow microcontrollers  a devices to communicate with each other within a vehicle without a host computer. 3. CAN is a message-based protocol, designed specifically for automotive applications but now also used in other areas such as industrial automation and medical equipment. 4. The Controller Area Network (CAN) bus is a serial asynchronous bus used in instrumentation applications for industries such as automobiles

Answer: SOF – 1 Dominant Arbitration Field – 11 bit Identifier, 1 bit RTR (or) 11 bit, 1SRR, 1IDE, 18 bit, 1RTR Control Field – IDE, r0, 4 bits (DLC) Data Field – (0-8) Bytes CRC Field – 15 bits, Delimiter (1 bit recessive) ACK Field – 1 bit, Delimiter (1 bit recessive) EOF – 7 bits recessive IFS – 3 bits recessive Types of frames – Data, remote, Error frame and Overload frame Types of errors – ACK error, Bit error, Stuff error, Form error, CRC error Error frame – 0-12 superposition flags, 8 recessive (Delimiter) Overload frame – 0-12 superposition flags, 8 recessive (Delimiter)

Answer: To minimize the reflection reference, to reduce noise. To ensure that reflection does not cause communication failure, the transmission line must be terminated.

Answer: CAN protocol is a message-based protocol, not an address based protocol. This means that messages are not transmitted from one node to another node based on addresses. Embedded in the CAN message itself is the priority and the contents of the data being transmitted. All nodes in the system receive every message transmitted on the bus (and will acknowledge if the message was properly received). It is up to each node in the system to decide whether the message received should be immediately discarded or kept to be processed. A single message can be destined for one particular node to receive, or many nodes based on the way the network and syste...

Answer: CSMA/CD + AMP (Arbitration on Message Priority) Two bus nodes have got a transmission request. The bus access method is CSMA/CD+AMP (Carrier Sense Multiple Access with Collision Detection and Arbitration on Message Priority). According to this algorithm both network nodes wait until the bus is free (Carrier Sense). In that case the bus is free both nodes transmit their dominant start bit (Multiple Access). Every bus node reads back bit by bit from the bus during the complete message and compares the transmitted value with the received value. As long as the bits are identical from both transmitters nothing happens. The first time there was a d...

Answer: Starts from MSB, first nibble is same, Master sends 7, slaves also sends 7 the message with more dominant bits will gain the arbitration, lowest the message identifier higher the priority.

Answer: Number of identifiers can be accommodated for standard frame are 2power11.  Number of identifiers more compare to base frame, for extended frame are 2power29. IDE bit – 1 for extended frame. IDE bit – 0 for Standard frame.

Answer: CAN uses a Non-Return-to-Zero protocol, NRZ-5, with bit stuffing. The idea behind bit stuffing is to provide a guaranteed edge on the signal so the receiver can resynchronize with the transmitter before minor clock discrepancies between the two nodes can cause a problem. With NRZ-5 the transmitter transmits at most five consecutive bits with the same value. After five bits with the same value (zero or one), the transmitter inserts a stuff bit with the opposite state.

Answer: Long NRZ messages cause problems in receivers • Clock drift means that if there are no edges, receivers lose track of bits • Periodic edges allow receiver to resynchronize to sender clock

Answer: The transceiver provides differential transmit capability to the bus and differential receive capability to the CAN controller. Transceiver provides an advanced interface between the protocol controller and the physical bus in a Controller Area Network (CAN) node. Typically, each node in a CAN system must have a device to convert the digital signals generated by a CAN controller to signals suitable for transmission over the bus cabling (differential output). It also provides a buffer between the CAN controller and the high-voltage spikes that can be generated on the CAN bus by outside sources (EMI, ESD, electrical transients, etc.). The can t...

Answer: LLC (Logical Link Control) – Overload control, notification, Message filtering and Recovery management functions. MAC (Medium Access Control) - Encapsulation/ de-capsulation, error detection and control, stuffing and de-stuffing and serialization/de-serialization.

Answer: Hard Synchronization to be performed at every edge from recessive-to-dominant edge during Bus Idle. Additionally, Hard Synchronization is required for each received SOF bit. An SOF bit can be received both during Bus Idle, and also during Suspend Transmission and at the end of Interframe Space. Any node disables Hard Synchronization if it samples an edge from recessive to dominant or if it starts to send the dominant SOF bit. Two types of synchronization are supported: – Hard synchronization is done with a falling edge on the bus while the bus is idle, which is interpreted as a Start of frame (SOF). It restarts the internal Bit Tim...