1. CAN Controller Area Network 29BIT ID
Overview and Application
Timothy E. Jackson

2. CAN Frame

3. CAN Frame IDENTIFIER DLC DATA FIELD Identifier = 29 bits + MAC
DLC = Data Length Code 4 bits
Indicates number of data bytes
Data Field = 0 to 7 bytes
Depends on the DLC value

4. Max frame length with bit stuffing = 127 bits
CAN Frame
CRC delimiter
1 bit
Standard Format, 2.0A
Max frame length with bit stuffing = 127 bits
Arbitration Field
Control Field
Data Field
12 bits
6 bits
0 to 64 bits
SOF
Identifier
11bits
RTR
IDE r0
DLC
4bits
CRC
15bits
ACK
Field
2bits
EOF
7bits
Bit Stuffing
No Bit
Stuffing
SOF = Start Of Frame
RTR = Remote Transmission Request
IDE = Identifier Extension Bit
DLC = Data Length Code
CRC = Cyclic Redundancy Check
ACK = Acknowledgement
EOF = End Of Frame

5. Max frame length with bit stuffing = 150 bits
CAN Frame
CRC delimiter
1 bit
Extended Format, 2.0B
Max frame length with bit stuffing = 150 bits
Arbitration Field
Control Field
Data Field
32 bits
6 bits
0 to 64 bits
SOF
Identifier
11bits
SRR
IDE
Identifier Ext.
18bits
RTR r1 r2
DLC
4bits
CRC
15bits
ACK
Field
2bits
EOF
7bits
Bit Stuffing
No Bit
Stuffing
SOF = Start Of Frame
SRR = Substitute Remote Request
IDE = Identifier Extension Bit
RTR = Remote Transmission Request
DLC = Data Length Code
CRC = Cyclic Redundancy Check
ACK = Acknowledgement
EOF = End Of Frame

6. CAN Frame 32 bits 6 bits 0 to 64 bits Arbitration Field Control Field
CRC delimiter
1 bit
Arbitration Field
Control Field
Data Field
32 bits
6 bits
0 to 64 bits
SOF
Identifier
11bits
SRR
IDE
Identifier Ext.
18bits
RTR r1 r2
DLC
4bits
CRC
15bits
ACK
Field
2bits
EOF
7bits

7. CAN Frame Message Structure 29 Bit Identifier DLC DATA FIELD 29 bits
0 to 8 bytes
PRI
PGN SA
PRI= Priority 3 bits
PGN = Parameter Group Number, 18 bits
SA = Source Address, 8 bits

8. How do I start using CAN right now?
SAE J1939
Defined by the automotive industry
Standards defined for the Layers 1,2,3,4, and 7

9. ISO Layers according to SAE J1939
Application Layer
SAE J1939/71
SAE J1939/73
Layer 7
Presentation Layer
Layer 6
Session Layer
Layer 5
Transport Layer
Layer 4
SAE J1939/21
Network Layer
SAE J1939/31
Layer 3
Data Link Layer
Layer 2
SAE J1939/21
Physical Layer
SAE J1939/11
SAE J1939/12
Layer 1

10. ISO Layers Used In EAMCS
Application Layer
Layer 7
Data Link Layer
Layer 2
Physical Layer
Layer 1

11. Physical Layer SAE J1939/11 – High Speed Bus Connection
Differential signal transmission
Shielded twisted pair bus lines and ground
250k bits/sec
30 nodes max.
Bus length = 40m max. or 131 ft. max.
SAE J1939/12 – Variant Bus Connection
Bus constructed using active termination
For bus load = 1 (Using 29bit ID and 8 data bytes per frame, approx. 135bits/message)
At a bitrate of 250kbps
1850 messages per second

12. Node A
(EAMCS)
Node B
(UQM Inverter)
120Ω
120Ω

13. Example MSCAN Timing

15. Cont. Example MSCAN Timing
16Tq = SYNC_SEG + PropagationDelaySeg + TimeSeg1 + TimeSeg2
SYNC_SEG = 1Tq
PropagationDelaySeg = 2Tq (Determined by bus characteristics)
Pick, TimeSeg2 = 5Tq
TimeSeg1 = 8Tq
This gives a SJW range 0…3 so, I picked 2
Once values are determined, then apply to MSCAN registers

16. Data Link Layer SAE J1939/21 29 Bit ID PRI PGN SA 28…26 25 24 23…16
15…8
7…0 r DP PF
DA/GE
PRI= Priority 3 bits
PGN = Parameter Group Number, 18 bits
r = Reserved Bit, always 0 or dominant
DP = Data Page
PF = PDU format, (Protocol Data Unit)
DA = Destination Address
GE = Group Extension
SA = Source Address, 8 bits

17. Example: EAMCS Message sent to UQM Inverter 29 Bit ID PRI r DP PDU
Dest. Addr
Source Addr
28…26 25 24
23…16
15…8
7…0
0x06
0x04
0xEF
0x02
0x01
Priority
Defined by SAE
Reserved for future use
Defined by SAE
PDU
Defined by SAE DA
Defined by User SA
Defined by User

18. Application Layer SAE J1939/71
Defines the bytes in the data field

19. SAE HANDBOOK DATA

20. Example: Parameter Group Definition
Electric Drive State
Transmission Repetition Rate: 100ms
Data Length: 8 bytes
Data Page: 0
PDU format: 239
PDU specific: DA
Default Priority: 4
Byte
Definitions 1
Command 0x10
2,3
Actual Speed 4
Torque 5
Voltage 6
Current
7,8
System Error

21. Cont. Example: Parameter Group Definition
Byte
Definitions 1
Command 0x10
2,3
Actual Speed 4
Torque 5
Voltage 6
Current
7,8
System Error
Definitions
Command
Actual Speed
Torque
Voltage
Current
System Error
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
Data Field

22. Cont. Example: Parameter Group Decoding Using MSCAN (The Easy Way)
Define a struct
typedef struct{
INT8U command; INT16U actual_speed; INT8U torque; INT8U voltage; INT8U current; INT16U system_error; }ELEC_DRIVE_STATE;
Command
Actual Speed (MSB)
Actual Speed (LSB)
Torque
Voltage
Current
System Error (MSB)
System Error (LSB)
CANRXFG[4] D a t F i e l d
Create an Instance
ELEC_DRIVE_STATE elec_drive_data;
Take advantage of Struct copying routines
elec_drive_data = *(ELEC_DRIVE_STATE*)(CANRXFG + 4);
Now access the data fields using the corresponding struct member
outhexw(&elec_drive_data.actual_speed); /* Print the 16bit hex value */

23. References Motorola Documentation
MSCAN Block Guide V02.14, S12MSCANV2.pdf
Bosch Documentation
CAN Specification Version 2.0, can2spec.pdf
Reference Texts
Konrad Etschberger,Controller Area Network. Weingarten, Germany: IXXAT Automation GmbH, 2001
1997 SAE Handbook, Volume 2 Parts and Components. Warrendale, PA: Society of Automotive Engineers, 1997