CAN INTERVIEW QUESTIONS:
Answer: 1. CAN is a multi-master broadcast serial bus preferred for connecting electronic manipulate unit (ECUs).
2. Controller–location network (CAN or CAN-bus) is a car bus preferred designed to allow microcontrollers a gadgets to speak with each different inside a car without a number laptop.
three. CAN is a message-based protocol, designed in particular for car applications however now extensively utilized in other areas which include business automation and clinical system.
four. The Controller Area Network (CAN) bus is a serial asynchronous bus utilized in instrumentation applications for industries consisting of motors.
– More reliably, e.g., fewer plug-in connectors that would motiveerrors.– Wiring less complicated, extra economic.– Easy to implement, changes, too.– Additional elements (e.g., control gadgets) are clean to integrate.– Installation location exchangeable without electric problems.– Wire may be identified.
Arbitration Field – 11 bit Identifier, 1 bit RTR (or) 11 bit, 1SRR, 1IDE, 18 bit, 1RTR
Control Field – IDE, r0, four bits (DLC)
CRC Field – 15 bits, Delimiter (1 bit recessive)
ACK Field – 1 bit, Delimiter (1 bit recessive)
Types of frames – Data, remote, Error frame and Overload body
Types of mistakes – ACK mistakes, Bit mistakes, Stuff error, Form mistakes, CRC blunders
Error body – 0-12 superposition flags, 8 recessive (Delimiter)
Overload frame – zero-12 superposition flags, 8 recessive (Delimiter)
three. Why CAN is having 120 ohms at each cease?
Answer: To decrease the reflection reference, to reduce noise. To make sure that mirrored image does now not motive communication failure, the transmission line have to be terminated.
4. Why CAN is message oriented protocol?
Answer: CAN protocol is a message-based protocol, no longer an deal with based totally protocol. This approach that messages aren’t transmitted from one node to every other node based totally on addresses. Embedded in the CAN message itself is the priority and the contents of the facts being transmitted. All nodes within the gadget receive each message transmitted on the bus (and could renowned if the message turned into properly acquired). It is up to each node within the machine to determine whether or not the message acquired ought to be without delay discarded or kept to be processed. A single message can be destined for one unique node to get hold of, or many nodes based at the manner the community and machine are designed. For instance, an automotive airbag sensor can be linked through CAN to a protection device router node only. This router node takes in other safety machine data and routes it to all other nodes at the safety machine network. Then all of the different nodes at the safety gadget network can obtain the ultra-modern airbag sensor information from the router on the same time, renowned if the message changed into obtained well, and determine whether or not to utilize this information or discard it.
five. CAN common sense what it follows?
6. What is CAN Arbitration?
Answer: CAN Arbitration is nothing however the node looking to take control at the CAN bus.
7. How CAN will observe the Arbitration?
Answer: CSMA/CD + AMP (Arbitration on Message Priority)
Two bus nodes have were given a transmission request. The bus get right of entry to technique 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 unfastened (Carrier Sense). In that case the bus is free each nodes transmit their dominant start bit (Multiple Access). Every bus node reads again step by step from the bus during the complete message and compares the transmitted cost with the obtained value. As lengthy as the bits are identical from both transmitters not anything happens. The first time there has been a distinction – in this situation the seventh bit of the message – the arbitration manner takes vicinity: Node A transmits a dominant degree, node B transmits a recessive stage. The recessive stage may be overwritten with the aid of the dominant level. This is detected through node B due to the fact the transmitted cost isn’t always identical to the acquired fee (Collision Detection). At this factor of time node B has misplaced the arbitration, stops the transmission of any similarly bit without delay and switches to receive mode, due to the fact the message that has received the arbitration should probable be processed by way of this node (Arbitration on Message Priority)
For example, bear in mind three CAN gadgets each trying to transmit messages:
• Device 1 – deal with 433 (decimal or 00110110001 binary)• Device 2 – address 154 (00010011010)• Device 3 – deal with 187 (00010111011)
Assuming all three see the bus is idle and start transmitting at the equal time, this is how the arbitration works out. All 3 devices will force the bus to a dominant country for the start-of-body (SOF) and the two maximum vast bits of every message identifier. Each tool will display the bus and decide success. When they write bit 8 of the message ID, the device writing message ID 433 will note that the bus is in the dominant state whilst it became looking to allow it’s recessive, so it’ll expect a collision and surrender for now. The ultimate devices will continue writing bits till bit 5, then the tool writing message ID 187 will word a collision and abort transmission. This leaves the tool writing message ID 154 remaining. It will preserve writing bits at the bus until whole or an mistakes is detected. Notice that this technique of arbitration will always purpose the lowest numerical fee message ID to have priority. This same method of bit-clever arbitration and prioritization applies to the 18-bit extension inside the prolonged format as properly.
8. What is the speed of CAN?
Answer: 40m @1Mbps and if the cable period increases will lower the speed, due to RLC at the cable.
nine. If grasp sends 764 and Slave sends 744 so one can get the arbitration?
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 better the priority.
10. Standard CAN and Extended CAN distinction?
Answer: Number of identifiers can be accommodated for wellknown body are 2power11.
Number of identifiers extra compare to base frame, for extended body are 2power29.
IDE bit – 1 for extended body.
IDE bit – zero for Standard body.
Answer: CAN makes use of a Non-Return-to-Zero protocol, NRZ-5, with bit stuffing. The idea behind bit stuffing is to offer a assured part on the signal so the receiver can resynchronize with the transmitter earlier than minor clock discrepancies between the two nodes can reason a trouble. With NRZ-5 the transmitter transmits at maximum 5 consecutive bits with the equal fee. After five bits with the same price (0 or one), the transmitter inserts a stuff bit with the other kingdom.
12. What is using bit stuffing?
Answer: Long NRZ messages reason issues in receivers
• Clock drift method that if there are not any edges, receivers lose song of bits
• Periodic edges allow receiver to resynchronize to sender clock
thirteen. What are the capabilities of CAN transceiver?
Answer: The transceiver gives differential transmit capability to the bus and differential acquire capability to the CAN controller. Transceiver provides an advanced interface between the protocol controller and the bodily bus in a Controller Area Network (CAN) node.
Typically, each node in a CAN system ought to have a tool to transform the digital indicators generated through a CAN controller to alerts suitable for transmission over the bus cabling (differential output). It also offers a buffer between the CAN controller and the excessive-voltage spikes that may be generated on the CAN bus by way of outside assets (EMI, ESD, electrical transients, and so forth.).
The can transceiver is a device which detects the signal ranges that are used on the CAN bus to the logical signal stages recognized through a microcontroller.
14. Functionality of Data link layer in CAN?
Answer: LLC (Logical Link Control) – Overload control, notification, Message filtering and Recovery management functions.
MAC (Medium Access Control) – Encapsulation/ de-capsulation, error detection and manage, stuffing and de-stuffing and serialization/de-serialization.
15. What is supposed by synchronization?
Answer: Synchronization is timekeeping which requires the coordination of activities to perform a machine in unison.
sixteen. What is supposed by using Hard synchronization and gentle synchronization?