Can protocol interview questions and answers in detail

The Bus Off state should only be left by a software reset. After software reset the CAN bus controller has to wait for 128 x 11 recessive bits to transmit a frame. This is because other nodes may have pending transmission requests. It is recommended not to start a hardware reset because the wait time rule will not be followed then.

CAN Protocol | Top 50 Question & Answers in CAN Protocol | Embedded World

When five consecutive bits of the same level have been transmitted by a node, it will add a sixth bit of the opposite level to the outgoing bit-stream. The receivers will remove this extra bit. This is done to avoid excessive DC components on the bus, but it also gives the receivers an extra opportunity to detect errors: if more than five consecutive bits of the same level occurs on the bus, a Stuff Error is signaled.

As you have seen in CAN frame format in above question only Arbitration field in the extended frame format only differ from the standard CAN means extended CAN architecture designed in such a way that standard and extended CAN coexist on the same network. In extended frame format, the IDE bit distinguish between the standard and extended CAN.

All nodes on the bus that correctly receives a message (regardless of their being “interested” of its contents or not) are expected to send a dominant level in the so-called Acknowledgement Slot in the message. The transmitter will transmit a recessive level here. If the transmitter can’t detect a dominant level in the ACK slot, an Acknowledgement Error is signaled.

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.).

CANopen is a high-level communication protocol and also a device profile specification that is based on the CAN (Controller Area Network)protocol. This protocol was developed for embedded networking applications, such as in-vehicle networks. It also covers a network programming framework, device descriptions, interface definitions, and application profiles. CANopen provides a protocol that standardizes communication between devices and applications from different manufacturers.

Originally Bosch released CAN specification CAN 2.0 for passenger Vehicles which explains 11- bit identifier frame architecture but later on it divided into CAN 2.0(A) which is named as standard CAN be used in passenger cars dealing with 11-bit Identifier while other is CAN2.0(B) which is known as extended CAN be used in heavy vehicles like Buses and Trucks it deals with 29-bit Identifier. So the basic difference in both standard at message Identifier field. For detail, frame architecture, Go through this article.

CSMA stands for Carrier Sense multiple Access.This concept is use in transmission media access.if multiple ECUs are connected on sharing same transmission medium to transfer its data then there is possibility of collision and data corruption if multiple nodes start transmission same time.CSMA introduce two concept CSMA/CA and CSMA/CD to avoid this situation.

Data frame will win the arbitration because the arbitration field contains Identifier+RTR. Here identifier is same but RTR is dominant in case of Data Frame while recessive in case of the remote frame.CAN bus works on wired and logic so 1&0=0. So the final value on CAN bus will be dominant(0). So Ecu which sends data frame(RTR=0) will get same value what it transmitted while ECU which sent remote frame will not get same value and consider that bus is busy and stop further transmission and wait for the bus to be idle and another ECU will continue its data frame transmission

CSMA/CD is Carrier Sense Multiple Access/Collision Detection. It is applicable when data transmission starts. A Node with CSMA/CD enabled feature detects the collision and stop the further data transmission. It will initiate data re-transmission. In CAN this feature is successfully implemented through Bit Monitoring feature of Transmitter node.see for detail bit monitioring Concept.

There are 5 types of error exist in CAN- Bit error, Stuff error, CRC error, Ack Error, Form Error. Some of the error detected by transmitters like Bit error and ACK error and some by the receiver like Stuff error, CRC error,Form Error.Go through with this article to know all about error detection.

FAQ

What are the interview questions on CAN?

The CAN protocol is a standard designed to allow the microcontroller and other devices to communicate with each other without any host computer. The feature that makes the CAN protocol unique among other communication protocols is the broadcast type of bus.

Which logic does a CAN protocol follow?

Practice CAN Protocol Interview Questions & Answers
  • 1) What is CAN Protocol? …
  • 2) Enlist major features of CAN Protocol? …
  • 3) List some applications of CAN Bus? …
  • 4) What are CAN Messages? …
  • 5) Explain high Speed CAN and Low Speed CAN? …
  • 6) What is standard CAN and Extended CAN? …
  • 7) What Is Can Arbitration? …
  • 8) What is SAE J1939?

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