MotoHawk Training
CAN
Controller Area Network
1
OUTLINE
• CAN Introduction
• CAN Physical Network
• CAN Message Format
• MotoHawk Block Walk Through
• MotoHawk “Post Office”
• MotoHawk Advanced CAN Blocks
• CAN Protocol Overview
2
INTRODUCTION
• CAN = Controller Area Network
 Communication 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
4
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
CAN -
CAN +
 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
5
120 Ω
Wire
Length
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
Module 0 continues
to transmit while Module 1
waits for next opportunity to
transmit
Module 0
Module 1
T0
6
T1
T2
T3
OUTLINE
• CAN Introduction
• CAN Physical Network
• CAN Message Format
• MotoHawk Block Walk Through
• MotoHawk “Post Office”
• MotoHawk Advanced CAN Blocks
• CAN Protocol Overview
7
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)
8
OUTLINE
• CAN Physical Network
• CAN Message Format
• MotoHawk Block Walk Through
• MotoHawk “Post Office”
• MotoHawk Advanced CAN Blocks
• CAN Protocol Overview
9
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
10
Send CAN Raw Block
11
CAN Exercise #1
• CAN Bus Test
Plug
(when not in use)
Short
Jumper or
SmartCraft
Cable
USB to Dual
CAN
Interface
 Construct a calibratable CAN message transmitter
 Use CANKing to monitor bus traffic
System Diagram
12
OUTLINE
• CAN Introduction
• CAN Physical Network
• CAN Message Format
• MotoHawk Block Walk Through
• MotoHawk “Post Office”
• MotoHawk Advanced CAN Blocks
• CAN Protocol Overview
14
POST OFFICE
• CAN is the hardware layer, so how are
transmitted messages sorted and
filtered in MotoHawk?
• A Post Office is the simplest analogy
 Mailboxes
 Letters
 Addresses
 Zip Codes
15
POST OFFICE
• Many messages are transmitted on a bus at a given time, but
a module may only be interested in a small subset
 Similar 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”
16
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?
17
POST OFFICE
• 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 mask is similar to assigning a
“Don’t Care” or a “Do Care” to a particular number
in the mask
18
Filtering
• 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 exactly
 For example,
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• 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
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
21
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
22
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 Block
 Exercise
• MotoHawk “Post Office”
• MotoHawk Advanced CAN Blocks
• CAN Protocol Overview
24
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
26
MOTOHAWK ADVANCED CAN
>> edit motohawk_can_example.m
27
LITTLE ENDIAN vs BIG ENDIAN
• 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)
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Address
Big Endian
Representation
Little Endian
Representation
00
0000 0000
0000 0001
01
0000 0000
0000 0100
02
0000 0100
0000 0000
03
0000 0001
0000 0000
• By default, the MotoHawk CAN scripts use Big
Endian byte ordering…which can lead to confusion
LITTLE ENDIAN vs BIG ENDIAN
Given this CAN definition byte ordering for a 4 byte variable:
Big Endian
Little Endian
LSB
63...….56
MSB
55...….48
47...….40
MSB
39...….32
Now, go let’s back to the script definition…
29
LSB
OUTLINE
• CAN Introduction
• CAN Physical Network
• CAN Message Format
• MotoHawk Basic Transmit Block
 Exercise
• MotoHawk “Post Office”
• MotoHawk Advanced CAN Blocks
• CAN Protocol Overview
30
CLASS EXERCISE
• Create a distributed control system to control
the ETC over CAN
Pedal
Duty Cycle
Analog signal from potentiometer
CAN message send
TPS %
City ID
0x81
CAN message receive
TPS %
Analog signal from ECT
Duty Cycle
CAN message receive
31
TPS %
CAN message send
Duty Cycle
PWM output
City ID
0x0B
CLASS EXERCISE
Duty Cycle message definition
CAN 1
CAN 1
ID Type : Standard (0)
ID Type : Standard (0)
ID : 0x1F4
ID : 0x2F4
Data Length : 2 Bytes
Data Length : 1 Byte
Transmission Rate : 10 ms
Transmission Rate : 15 ms
Data Field
Data Field
Duty Cycle (SIGNED)
Scale : 200/65,535
Offset : 0
Start bit: 48
Size: 2 bytes
32
TPS Percent message definition
TPS Percent (UNSIGNED)
Scale : 100/255
Offset : 0
Start bit: 56
Size: 1 byte
PROTOCOL OVERVIEW
• CAN gets complicated when protocols are considered
 J1939, 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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MotoTron Control Solutions
Production Controls in a Flash