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CANController Area Network

MotoHawk Training

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OUTLINE

• CAN Introduction

• CAN Physical Network

• CAN Message Format

• MotoHawk Block Walk Through

• MotoHawk “Post Office”

• MotoHawk Advanced CAN Blocks

• CAN Protocol Overview

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INTRODUCTION

•CAN = Controller Area NetworkCommunication specification implemented for automotive

applications in the 1980s•Often, the term “CAN” is misused

CAN is a hardware definition for interoperability between modules

CAN specification does not state the data content of a given message

Protocols built on top of CAN state the data content (ex. J1939, GMLAN)

•MotoHawk doesn’t define a protocol, but allows access to the CAN hardware to implement a protocol

•By itself, CAN is not difficult (I mean it)

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OUTLINE

• CAN Introduction

• CAN Physical Network

• CAN Message Format

• MotoHawk Block Walk Through

• MotoHawk “Post Office”

• MotoHawk Advanced CAN Blocks

• CAN Protocol Overview

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PHYSICAL NETWORK

• Two wire robust serial communication

• Up to 1Mbps data rate which is limited by wire length 100 m @ 250Kbps 30 m @ 1Mbps

• Termination resistance required• Maximum bandwidth

2000 messages per second @250Kbps

4000 messages per second @500Kbps

8000 messages per second @1Mbps

• Designed bandwidth should not exceed 70% of the maximum bandwidth

120 Ω

CAN + CAN -

WireLength

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PHYSICAL NETWORK

• Bus arbitration is handled with a simple strategy All modules on the bus attempt to transmit a message at the same

time The message with the lowest address wins

• This strategy is handled at the hardware level Dominant Bits (0) vs. Recessive Bits (1)

• Multiple modules on the same bus cannot transmit the same address at the same time

T0 T1 T2 T3

Module 0

Module 1

Module 0 continues to transmit while Module 1waits for next opportunity to transmit

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OUTLINE

• CAN Introduction

• CAN Physical Network

• CAN Message Format

• MotoHawk Block Walk Through

• MotoHawk “Post Office”

• MotoHawk Advanced CAN Blocks

• CAN Protocol Overview

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MESSAGE FORMAT

•A CAN 2.0B Message can contain up to 131 bits

•As application developers, 3 fields are important:4 bits determine the length of the data (aka payload)

(Range : 0-8)Up to 64 bits of data depending on data length ID Format

• Extended IDs are 29 bits• Standard IDs are 11 bits• Extended and Standard IDs can exist on the same bus at the same

time• Standard IDs have less message overhead (higher percentage of

data per message)

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OUTLINE

• CAN Physical Network

• CAN Message Format

• MotoHawk Block Walk Through

• MotoHawk “Post Office”

• MotoHawk Advanced CAN Blocks

• CAN Protocol Overview

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CAN DEFINITION BLOCK

•First, the CAN hardware needs to be initialized

•Baud rate and transmit queue size configured

• If the baud rate and/or MotoTune protocol settings are not configured properly, then MotoTune can’t talk to the module via CAN (and therefore programming cannot be performed via CAN)Boot key sets CAN baud rate to 250kbps

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Send CAN Raw Block

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• CAN Bus Test Construct a calibratable CAN message transmitter Use CANKing to monitor bus traffic

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CAN Exercise #1

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OUTLINE

• CAN Introduction

• CAN Physical Network

• CAN Message Format

• MotoHawk Block Walk Through

• MotoHawk “Post Office”

• MotoHawk Advanced CAN Blocks

• CAN Protocol Overview

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POST OFFICE

• CAN is the hardware layer, so how are transmitted messages sorted and filtered in MotoHawk?

• A Post Office is the simplest analogyMailboxesLettersAddressesZip Codes

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POST OFFICE

• Many messages are transmitted on a bus at a given time, but a module may only be interested in a small subsetSimilar to a post office where the messages are letters and

the software dispatcher is the postman

A “mail box” in MotoHawk is called a “slot”

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POST OFFICE

• A “slot” has an address known as a CAN ID similar to the address on a mailbox

• The MotoHawk post office needs to deliver messages to these slots

• How does it happen?

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POST OFFICE

•Filtering is done with 2 masks ID Mask : Filters a message by the address or the IDPayload Mask : Filters a message by the data content

•A mask is similar to assigning a “Don’t Care” or a “Do Care” to a particular number in the mask

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•Filtering is done with 2 masks ID Mask : Filters a message by the address or the ID Payload Mask : Filters a message by the data content

•A ‘1’ in the mask means that the data and the value must match exactlyFor example,

• if ID mask = 0x7F0 (111 1111 0000)

• and ID = 0x7E4 (111 1110 0100)

• If incoming ID = 0x7E0, (111 1110 0000)

message goes to mailbox

• If incoming ID = 0x7F4, (111 1111 0100)

x message is rejected by mailbox

• If incoming ID = 0x7E1, (111 1110 0001)

message goes to mailbox

Filtering

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READ CAN RAW BLOCK

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POST OFFICE

•The “Slot Name” is the name of the mailbox at the post office

•The slot has default settings for the ID, ID Mask, Payload Value, and Payload Mask

•This is the design time mailbox configuration

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POST OFFICE

• The properties of the mailboxes can be changed at run time• The filters determined at design time can be strengthened

(more restrictive), but cannot be weakened

• In MotoHawk, the CAN Receive Slot Properties Block allows the user to change the filters at run time

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POST OFFICE

• What happens if the postal worker rings your doorbell to deliver a message? This is an asynchronous reception of a message The advantage is that processing time can be saved by not

periodically polling this message

• How does MotoHawk handle this situation? Asynchronous reception processed with CAN Receive Slot Trigger

Block Slot name in this block must match the slot name specified in Read

CAN Raw block or Read CAN Message block

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OUTLINE

• CAN Introduction

• CAN Physical Network

• CAN Message Format

• MotoHawk Basic Transmit BlockExercise

• MotoHawk “Post Office”

• MotoHawk Advanced CAN Blocks

• CAN Protocol Overview

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MOTOHAWK ADVANCED CAN

•The Read and Send CAN blocks are nice, but sometimes more advanced data parsing is necessary. Common questions: I have 12 bit scaled data that spans across multiple bytes.

How do I convert it into engineering units? I have more data that can fit into 64 bits. How do I create

multi-page messages? I’m using a protocol that has a variable ID. How do I

dynamically create the ID easily?

•These are valid questions and there is an answer…

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MOTOHAWK ADVANCED CAN

• MotoHawk has 2 blocks – Read CAN Message and Send CAN Message (below)

• These are very powerful blocks that allow users to set up multi-page documents and parse and scale both variables and IDs

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MOTOHAWK ADVANCED CAN

>> edit motohawk_can_example.m

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• Terminology originates from “Gulliver’s Travels”

• “Endianness” refers to the order in which bytes are stored in memory

• This table shows the 4 byte storage for 1025 (0x41)

• By default, the MotoHawk CAN scripts use Big Endian byte ordering…which can lead to confusion

Address Big Endian Representation

Little EndianRepresentation

00 0000 0000 0000 0001

01 0000 0000 0000 0100

02 0000 0100 0000 0000

03 0000 0001 0000 0000

LITTLE ENDIAN vs BIG ENDIAN

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63...….56

55...….48

47...….40

39...….32

Given this CAN definition byte ordering for a 4 byte variable:

LSB

Big Endian

MSB

Little Endian

LSB

MSB

Now, go let’s back to the script definition…

LITTLE ENDIAN vs BIG ENDIAN

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OUTLINE

• CAN Introduction

• CAN Physical Network

• CAN Message Format

• MotoHawk Basic Transmit BlockExercise

• MotoHawk “Post Office”

• MotoHawk Advanced CAN Blocks

• CAN Protocol Overview

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•Create a distributed control system to control the ETC over CAN

Pedal

Duty Cycle

TPS %

CAN message receive

Analog signal from ECT

TPS %

CAN message send

Duty Cycle

PWM output

Duty Cycle

CAN message send

TPS %

CAN message receive

Analog signal from potentiometer

City ID 0x0B

City ID 0x81

CLASS EXERCISE

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CLASS EXERCISE

Duty Cycle message definition

CAN 1

ID Type : Standard (0)

ID : 0x1F4

Data Length : 2 Bytes

Transmission Rate : 10 ms

Data Field

Duty Cycle (SIGNED)Scale : 200/65,535Offset : 0 Start bit: 48 Size: 2 bytes

TPS Percent message definition

CAN 1

ID Type : Standard (0)

ID : 0x2F4

Data Length : 1 Byte

Transmission Rate : 15 ms

Data Field

TPS Percent (UNSIGNED)Scale : 100/255Offset : 0 Start bit: 56 Size: 1 byte

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PROTOCOL OVERVIEW

• CAN gets complicated when protocols are consideredJ1939, SmartCraft, CCP, GMLAN, etc. are all examples of

protocols that adhere to strict rules

• These protocols can be implemented using Simulink and/or Stateflow

• Some message formats (J1939) have already been implemented for other projects

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