I2C and CAN Protocol

7/29/2019 I2C and CAN Protocol

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SERIAL BUSCOMMUNICATION

PROTOCOLS

& CAN


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PROTOCOLS

Protocol


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Introduction to I2C

I2C is well known bus invented by PHILIPS.

I2C stands for INTER-INTEGRATED CIRCUIT.

These type of bus is famous in TV circuit board and then itcome to computer environment.

It has speed of 100kbs but it can be extended to 450kbps.

But only the problem is our processor has a capability ofI2C protocol bus inbuilt.


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Technical Specifications

The I2C Bus has two lines that carry its signals one line is for clock named as SCL and second isfor data named as SDL.

By using I2C protocol the master can address 127slaves at an instances.

It has a processing element functionally as a buscontroller or a microcontroller with I2C businterface circuits.


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Bit format of I2C


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Brief introduction by video session


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State Diagram of I2C BusMaster

Idle

Address

DATAWrite

DATARead

Get

DATA

Send

DATA


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PROTOCOLSCAN Protocol


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DistributedControl Area Network (CAN)Bus Distributed Control Area Network

Example - a network of embedded systems inautomobile

It has a speed of 1 Mbps as a data rate

It uses Multi-master bus.

CAN Module are required


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CAN is a closed network

no need for security, sessions or logins.

- no user interface requirements.

Physical and Data Link layers in silicon.

CANBUS and the OSI Model

10OSI:-> Open Systems Interconnection


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CANBUS Physical Layer

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Conventional multi-wire looms CAN bus network

Physical medium two wires terminated at both ends by resistors.

Differential signal - better noise immunity.

Benefits: Reduced weight, Reduced cost

Fewer wires = Increased reliability

vs.

http://canbuskit.com/what.php


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Message Oriented Transmission Protocol

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Each node receiver & transmitter

A sender of information transmits to all devices on the bus

All nodes read message, then decide if it is relevant to them

All nodes verify reception was error-free

All nodes acknowledge reception

CAN bus 2005 Microchip Technology Incorporated. All Rights Reserved.


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Message Format

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Each message has an ID, Data and overhead.

Data8 bytes max Overhead start, end, CRC, ACK


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Bus Arbitration

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Arbitration needed when multiple nodes try to transmit at the same time

Only one transmitter is allowed to transmit at a time.

A node waits for bus to become idle

Nodes with more important messages continue transmitting

CAN bus 2005 Microchip Technology Incorporated. All Rights Reserved.


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Bus Arbitration

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Message importance is encoded in message ID.

Lower value = More important As a node transmits each bit, it verifies that it sees the same bit

value on the bus that it transmitted.

A 0 on the bus wins over a 1 on the bus.

Losing node stops transmitting, winner continues.


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CAN protocol

There is a CAN controller between the CAN line andthe host node.

CAN controllerBIU (Bus Interface Unit) consisting

of a buffer and driver

Method for arbitrationCSMA/AMP (Carrier SenseMultiple Access with Arbitration on MessagePriority basis)


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Each Distributed Node Uses:

Twisted Pair Connection up to 40 m for bi-directional data.

Line, which pulls to Logic 1 through a resistor

between the line and + 4.5V to +12V. :

Line Idle state Logic 1 (Recessive state)

Detects Input Presence at the CAN line pulleddown to dominant (active) state logic 0 (ground ~0V) by a sender to the CAN line


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It has two states

1. Dominant State(Logic 0)

2. Recessive State(Logic 1)

Physical Layer


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Data Link Layer

Bit Format of CAN Bus

There are 5-fields in CAN data Frame Format and START & STOP Bits

1. Arbitration field

2. Control Field [Specifies the number of bytes of data to follow (0-8)]

3. Data Field

4. CRC Field [cyclic redundancy check code]

5. Acknowledge Field

START

ARBITRATION

FIELD

CONTROL

FIELD

DATA

FIELD

ACK

FIELD

END

FRAME

1 BIT 12 BITS 6 BITS 0 TO 64 BITS

CRC

FIELD

16 BITS 2 BITS 7 BITS


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Protocol defined First field inframe bits

First field of 12 bitsArbitrationfield.

11-bit destination address and RTR bit (RemoteTransmission Request)

Destination device address specified in an 11-bit sub-field and whether the data byte being sent is a data forthe device or a request to the device in 1-bit sub-field.

Maximum 211 devices can connect a CAN controller incase of 11-bit address field standard


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Arbitration Field

Identifies(11 bits) the device to which data is beingsent or request is being made.

When RTR bit is at '1', it means this packet is for

the device at destination address. If this bit is at '0'(dominant state) it means, this packet is a requestfor the data from the device.


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Second field of 6 bits- control field.

The first bit is for the identifiers extension.

The second bit is always '1'.

The last 4 bits specify code for data length

Control Field (6 bits)


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Third field of 0 to 64 bits

Its length depends on the data length code in thecontrol field.

Data Field (up-to 8 bytes data)


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Fourth field (third if data field has no bit present)of 16 bitsCRC (Cyclic Redundancy Check) bits.

The receiver node uses it to detect the errors, if

any, during the transmission

CRC Field


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Fifth field of 2 bitsFirst bit 'ACK slot'

ACK = '1 BIT' and receiver sends back '0' in this slot whenthe receiver detects an error in the reception.

Sender after sensing '0' in the ACK slot, generallyretransmits the data frame.

Second bit 'ACK delimiter' bit. It signals the end of ACKfield.

If the transmitting node does not receive anyacknowledgement of data frame within a specified timeslot, it should retransmit.

ACK Field


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Sixth field of 7-bits

end- of- the frame specification and has seven '0's

EOF Field

S


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CAN busController Area Network bus Primarily used for building ECU (Engine control

unit) networks in automotive applications.

Two wires

OSI - Physical and Data link layers

Differential signal - noise immunity

1Mbit/s, 120

Messages contain up to 8 bytes of data

Summary

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http://en.wikipedia.org/wiki/Engine_control_unithttp://en.wikipedia.org/wiki/Engine_control_unithttp://en.wikipedia.org/wiki/Engine_control_unithttp://en.wikipedia.org/wiki/Engine_control_unithttp://en.wikipedia.org/wiki/Engine_control_unit


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Self Study

USB Protocol..!!!

Date post:	14-Apr-2018
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I2C and CAN Protocol

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