Introduction Standard to establish Network among microcontrollers Broadcast type of bus No way to send a message to a specific node High speed applications with short messages
Comparing W ith Other Buses Bus Transfer Type Transfer Rate Max. Length (m) No. Of Nodes (b/s) RS232 Point to point 20k 15 1 RS485 Network 35k 1200 32 I2C Master-Slave 100k 1 128 SPI Master-Slave 110k 1 any CAN Network 1M 40 2032 USB Master-Slave 480M 5 126
CAN in general……… Multi-master Network 2-wire Half-duplex High-speed (1Mbps) Error Confinement and Error Detection Distance up to 6 mS
Histor y Introduced by Robert Bosch in 1986 Developed for automotive applications Standardized in 1993 as ISO11898-1 CAN Standards 1. CAN 2.0A 2. CAN 2.0B
CAN Standar ds1. CAN 2.0A Standard CAN (ISO 11898) 11-bit Identifier 1 Mbps2. CAN 2.0B Extended CAN (ISO 11519) 29-bit Identifier 125 kbps
Reasons for Using CAN Robustness & Reliability Low Connect Cost Low Cost Components Availability of CAN based Products
Applications In Industry To interconnect Machines, Process Control Units and Production Sub-systemIn Building Automation To manage Heating, Lighting, Air ventilation and doors Parameter Setting and control of equipment in agriculture
Layer ed Str uctur e Application Layer Message Filtering, Message and Object Status HandlingFault Confinement, Layer Error Detection, Signaling,Message Validation, TransferAcknowledgement, Layer Arbitration, Framing, Transfer Rate Physical and Layer Timing Transmission Medium, Signal Level and CAN bit representation Network
Networ k Components Cables Physical Layer Connectors Transceivers Part A CAN Controller Part B Passive Part B Software
CablesTwisted Pair Cables are used to get higher speeds. The Bitrate of the data transformation is high for short distanceand low for long distance. Bus Length Bit Rate 40 Meters 1 Mbps 100 Meters 500 kbps 200 Meters 250 kbps 500 Meters 125 kbps 6 meters 10 kbps
Connector s Pin Number Name Specification 1 - Reserved 2 CAN_L CAN_L bus line (dominant low) 3 CAN_GND CAN Ground 4 - Reserved 5 CAN SHLD Optional CAN Shield 6 GND Optional CAN Ground 7 CAN_H CAN_H bus line (dominant high) 8 - Reserved 9 CAN_V+ Optional Power ll Mini type r maN o ed y Us Pin Number Name 1 Drain 2 V+ 3 V- 4 CAN_H 5 CAN_L
CAN Contr oller s Part A → 11-bit Identifier → Above 2000 devices in the Network Part B Passive → 11-bit Identifier → Tolerated 29-bit Identifier, but ignored Part B → 29-bit Identifier → Above 5 million devices in the Network
Wor king Principle Uses CSMA/CD+AMP (Arbitration on Message Priority). Data messages transmitted from any node Using identifier all nodes will check whether the message is intended for it or not The identifier determines the priority of the message Low bits are always dominant
Data Fr ame (Messa ge Frame) For 2.0AStart Of Frame: Logic 0 indicates the beginning of a message frame.Arbitration Field: 11-bit identifier. Determines the priority of themessage.Control Field: 6-bits. 2-bits are reserved for future use. 4-bit DataLength Code (DLC) indicates the number of bytes in the datafield.
Data Field: 0 to 8 Bytes of dataCRC Field: 15-bits Cyclic Redundancy Check Code and 1-bitdelimiterAcknowledgement Field: 2-bits. Slot bit (1) overwritten by dominant bit fromother nodes and delimiter bit (1).End Of Frame Field: 7-bits (1111111). Indicates the End of the dataframe. Following the End Of Field is the Intermission fieldconsisting of 3-bits (111) denotes the bus is recognized to be
For 2.0B SRR (Substitute Remote Request) IDE (Identifier Extension) The max. no. of user in 2.0A is 2032 The max. no. of user in 2.0B is above 5 million
Remote Fr ameThe intended purpose of this frame is to ask for thetransmission of the corresponding data frame. It is also usedimplement a type of request-response type of bus trafficmanagement.
Er ror Fr ameConsists of error flag (6-bits) and error delimiter (8-bits).Transmitted when a node detects a fault and will cause allother nodes to detect a fault
Over load FrameThis frame is mentioned just for completeness of thetransaction.
Er ror Detection and Confinement Error is detected by the CAN Controller Error Frame is transmitted Message is cancelled at all nodes Status of the CAN Controllers are updated The message is retransmitted
Types Of Er r or s Bit Error – The node always reads the message as it is sending. If it find a different value on the bus than it send, it detects the bit error. Bit Stuffing Error – If a receiving node found more than five consecutive bits it detects the error. Checksum Error Frame Error – Invalid bit error Acknowledgement Error
Er ror Modes Error Active – Active Error Flag is send and the data are transmitted and received usually Error Passive – When Controller has frequent problems and Passive Error Flag is sent Bus Off – When controller has serious problems . No messages can be transmitted or received
Er ror ProcessTwo Error Counters are allocated for controlling the error mode. Theerror counters are transmit error count and receive error count
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