Can And Can Fd

Controller Area Network Flexible Data

Increased length: up to 64 data bytes per data frame vs. 8 data bytes for Classical CAN
Increased speed: up to 5 Mbit/s

-SOF
-IDENTIFIER
-RRS: Remote Request Substitution
(always a dominant 0). The remote frames are not at all supported in CAN FD.
-IDE: for future use/e. Dominant
-EDL: Extended Data Length
(always a recessive 1) for managing larger payloads and faster bit-rates in CAN FD.
-FDF: Flexible Data Rate Format
(always a recessive 1) used to indicate Flexible data frame format usage.
-BRS: Bit Rate Switch
helps determine the bit rate of a data frame.
Dominant 0 signifies that the arbitration rate is up to 1Mbit/sec.
Recessive 1 signifies a higher/faster arbitration rate is up to 5Mbit/sec.
-ESI: Error State Indicator
A dominant 0 indicates the error-active mode.
A recessive 1 indicates the error-passive mode.
CRC: The Cyclic Redundancy Check is 17 bits long for up to 16 bytes of data or 21 bits for 20-64 bytes. Its length depends upon the length of EDL and DLC bits. CAN FD always uses 4-fixed stuff bits that improve communication reliability.
-DLC: 4 bits

Controller Area Network. Created by Bosch. Communication could be started by any node

CAN It is multimaster. Frame size = 8 Bytes of data

•SOF: The Start of Frame is a 'dominant bit' '0' to tell the other nodes that a CAN node intends to talk
•ID: The ID is the frame identifier - lower values have higher priority
Message ID = Lower the value, higher the priority.
•RTR: distinguish data and remote frame(0=Data frame, 1=Remote frame)
•IDE: IDE to differentiate standard and extended frame. Always recessive bit, 1.
•R0: Is used to differentiate CAN and a CAN-FD frame. Always recessive bit, 1.
•DLC: determine data size and message ID length
•Data: The Data contains the data bytes aka payload, which includes CAN signals that can be extracted and decoded for information
Data frame = Standard frame(11 bit) or extended frame(29 bit)
•CRC: The Cyclic Redundancy Check is used to ensure data integrity
•CRC Delimiter: be ready for ACK. Recessive 1.
•ACK: The ACK slot indicates if the node has acknowledged and received the data correctly
•ACK delimiter: 1 bit recessive
•End Of Frame: 7 recessive bits
•IFS: Minimum 3 recessive bits

Simplex = Send > Receive
Full-duplex = Send > Receive, Receive < Send (At the same time is sending and receiving)
Half-duplex = Send > Receive, Receive < Send (Not possible at the same time is sending and receiving)
CAN is half-duplex

Parallel communication = N of bits > 1
Serial communication = N of bits = 1
CAN is serial communication protocol

Twisted pair = CanHigh and CanLow. It is twisted pair for noise immunity, Twisted pair ends with a 120 ohms resistor for impedance matching = minimize signal reflection

Logic 1 = Recessive bit = CANH and CANL are equal to 2.5 v

Logic 0 = Dominant bit = CANH equal to 3.5v CANL equal to 1.5 v

CAN speed = 1 MbPS. 1 MbPS at 40 mts

CAN is asynchronous = It can start to communicate whenever it wants.
Synchronous Communication – Each bit of data drive syncs with a clock signal and the master drives the clock signal means the master can only initiate data communication.

11 y 29 bit identifier

Data Frame, Remote Frame, Error Frame and Overload Frame

Application Layer: MCU(host controller)
Data Link Layer: CAN Controller
Physical Layer: CAN Transceiver, CAN Bus medium, CAN Bus connector

NRZ (Non Return to Zero)

CAN standard allowed only 5 consecutive bits of same polarity and after that signal must change its polarity to check synchronization between transmitter and receiver. If any transmitter wants to send more than 5 consecutive bits then it must insert an opposite signal bit and it is called bit stuffing and this extra stuff bit is de-stuffed by receiver before data processing.

Bit error = Every transmitter node reads back its transmitted bit from CAN line along with other ECUs But if it will not get read bit same as it transmitted then transmitted node stop the further transmission and introduce an error frame on CAN line
Stuff error = More than 5 consecutive bits of the same polarity
CRC error =If the receiver found Calculated CRC is different from received CRC
Acknowledgment error = if the transmitter read back a recessive bit as ACK (Receiver should covert it as dominant and send it back)
Form Error = CAN Frame Format(CRC Delimeter, ACK Delimeter, EOF ,InterFrame Spaceand) if it is detected corrupted at receiver side, length or format

High Speed CAN Vs Low Speed CAN

-100 ohm resistance
-Maximum bit rate is 40K to 125 kbps
-For dominant signal transmission, CAN_H drives towards 5 v while CAN_L drives toward 0.
-Rececive 1 = CANL 5V and CANH 0V
-Dominant 0 = CANH 3.5V and CANL 1.5
-

Standard Frame Format for Passenger Vehicles

Extended Frame Format for Heavy Vehicles

An ECU can also request to another ECU present on CAN Bus for data frame if required. This request for Data Frame is done through this FRAME

`1. For Remote Frame, Data field will not be the part of remote frame.

2. For Remote Frame ,RTR field must be recessive(1).

3. In Remote Frame, no data field But DLC field will exist as it shows the requested data size.

1. Error Flag(6-12 dominant/recessive bits)

2. Error Delimiter(8 recessive bits)

Error Flag may be dominant or recessive, it all depends on the error type.

substitute remote request

All nodes are connected on a differential cable terminated with a register. Any node can be connected or disconnected without disturbing other nodes on the network.

Any node can broadcast message on CAN Bus and all other nodes can listen to this broadcasted message including transmitter but its receiver’s choice to receive the message or not i.e it’s not address based protocol which is used for peer to peer transmission.

In a vehicle, many ECUs are very safety critical so there message would be processed at a higher priority and CAN protocol do it by assigning lower identifier value.So manufacture can decide the message priority by assigning them Identifier value(Lower the Identifier highr the Priority)

Carrier sense multiple access collision avoidanc is used to check bus status and if it is free then the node will transmit data or it would wait for idle status. CSMA/CD is collision detection means it would direct for the stop transmission if data is corrupted on CAN bus(means data is mixed up with other Node data i.e collision).This way transmitter save its time and retransmit it’s data when bus is idle.

Every CAN node has self-error diagnostic and recovery state. Every node has TEC(Transmit error Counter) and REC(Receive Error Counter) to categories its error state(error Active, Passive, Bus off). If CAN node reaches in Bus-OFF (When TEC>255) state then it will disconnect itself from CAN Network without disturbing other nodes. This feature makes CAN protocol very reliable.
Active Error state(When TEC<=127 and REC<=127)
Passive Error state( When TEC>127 or REC>127 )

1. Host Controller: It process data from the Application layer to the network layer and vice versa.
2.CAN Controller: take care of the message reception and transmission, error detection and handling etc.
3.CAN Transceiver: convert the CAN controller data into bus level before sending on CAN Bus and vice-versa

is the process which decides the owner of CAN bus if two nodes started message broadcasting at the same time .

Every transmitter reads back its transmitted bit from the CAN bus to ensure its transmitted data Integrity

Every node connected on a CAN network may be transmitter and receiver as well. If any node transmits some frame on CAN then all other will be listener along with the transmitter itself i.e a transmitter also read back its data from CAN line to ensure the Integrity of transmitted data