CAN- controlled area network

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 ds

1. CAN 2.0A
Standard CAN (ISO 11898)
11-bit Identifier
1 Mbps

2. 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-system

In 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 Handling
Fault Confinement, Layer
Error Detection,
Signaling,
Message Validation, Transfer
Acknowledgement, 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

Cables
Twisted Pair Cables are used to get higher speeds. The Bit
rate of the data transformation is high for short distance
and 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 ma
N 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

→ Tolerated 29-bit Identifier, but ignored
 Part B

→ 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

Frame Types
 Data Frame
 Remote Frame
 Error Frame
 Overload Frame

Data Fr ame
(Messa ge Frame)
For 2.0A

Start Of Frame:
Logic 0 indicates the beginning of a message frame.
Arbitration Field:
11-bit identifier. Determines the priority of the
message.
Control Field:
6-bits. 2-bits are reserved for future use. 4-bit Data
Length Code (DLC) indicates the number of bytes in the data
field.

Data Field:
0 to 8 Bytes of data
CRC Field:
15-bits Cyclic Redundancy Check Code and 1-bit
delimiter
Acknowledgement Field:
2-bits. Slot bit (1) overwritten by dominant bit from
other nodes and delimiter bit (1).
End Of Frame Field:
7-bits (1111111). Indicates the End of the data
frame.
Following the End Of Field is the Intermission field
consisting 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 ame

The intended purpose of this frame is to ask for the
transmission of the corresponding data frame. It is also used
implement a type of request-response type of bus traffic
management.

Er ror Fr ame

Consists of error flag (6-bits) and error delimiter (8-bits).
Transmitted when a node detects a fault and will cause all
other nodes to detect a fault

Over load Frame

This frame is mentioned just for completeness of the
transaction.

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

Difference Between CAN, LIN, I2C
protocol I2C SPI CAN

Protocol Synchronous interface used on PCB Synchronous interface used on PCB CAN is Asynchronous Interface &
uses wires for long distance
communications.

Invented Philips Motorola Bosch

Data rate I2C Supports Speed is : SPI Supports : 3Mbps to 10Mbps 10Kbps to 1 Mbps
100Kbps(Standard)
:400Kbps(Fast) :
3.4Mbps(High Speed)

master I2C is multi-master, Address SPI is Master Slave, With Slave MultiMate , Message based
based Communication select(SS) based communications, Reliable
Communication

Pins required I2C needs 2 pins SPI needs 3+n pins (n is no. of CAN H and CAN L
devices)

supports I2C supports 127 devices limited by available Chip selects 2043 devices

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Dif ference Between CAN,
LIN, I2C
protocol I2C SPI CAN
communication I2C is half duplex as there are only SPI is Full Duplex as between a Half duplex
two lines(SCL and SDA) Master and a dedicated slave as
selected by slave select signal;
there are 4 lines
(Spi_clk,Spi_datain,Spi_dataout
and slave select).So, at any given
time data can be sent and received
by the master on two separate
lines.
whereas the I2c is generally used in whereas the SPI is generally used in CAN is generally used for device
same PCB same PCB net (different device at different
location)
bus arbitration is possible in case not in case of spi.
of i2c.

noise sensitivity of i2c is high... But in case of spi.. Chance is very
there is chance to corrupt the r/w less as whole word is transmitted.
bit... then whole data is corrupted
Single duplex Full duplex operation Half duplex

© 2008 Pantech Solutions™ | All rights reserved | www.panetchsolutions.net

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 Process
Two Error Counters are allocated for controlling the error mode. The
error counters are transmit error count and receive error count

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CAN- controlled area network

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