ETC BCANPSV2.0

Freescale Semiconductor, Inc.
PROTOCOL STANDARD
Freescale Semiconductor, Inc...
BCANPSV2.0
BCANPSV2.0/D
Rev. 3
CAN
Bosch Controller Area
Network (CAN)
Version 2.0
PROTOCOL
STANDARD
!MOTOROLA
!MOTOROLA
For More Information On This Product,
Go to: www.freescale.com
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
Freescale Semiconductor, Inc.
INTRODUCTION
BASIC CONCEPTS
MESSAGE TRANSFER
Freescale Semiconductor, Inc...
ERROR HANDLING
FAULT CONFINEMENT
BIT TIMING REQUIREMENTS
INCREASING OSCILLATOR TOLERANCE
INTRODUCTION
BASIC CONCEPTS
MESSAGE TRANSFER
ERROR HANDLING
FAULT CONFINEMENT
BIT TIMING REQUIREMENTS
THE MOTOROLA CAN (MCAN) MODULE
TOUCAN
THE MOTOROLA SCALEABLE CAN (MSCAN08) MODULE
THE MOTOROLA SCALEABLE CAN (MSCAN12) MODULE
1
2
3
4
5
6
7
8
9
10
11
12
13
A
B
C
D
TPG
For More Information On This Product,
Go to: www.freescale.com
1
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
1
2
3
4
5
6
7
8
9
10
11
12
13
A
B
C
D
INTRODUCTION
BASIC CONCEPTS
MESSAGE TRANSFER
ERROR HANDLING
FAULT CONFINEMENT
BIT TIMING REQUIREMENTS
INCREASING OSCILLATOR TOLERANCE
INTRODUCTION
BASIC CONCEPTS
MESSAGE TRANSFER
ERROR HANDLING
FAULT CONFINEMENT
BIT TIMING REQUIREMENTS
THE MOTOROLA CAN (MCAN) MODULE
TOUCAN
THE MOTOROLA SCALEABLE CAN (MSCAN08) MODULE
THE MOTOROLA SCALEABLE CAN (MSCAN12) MODULE
TPG
For More Information On This Product,
Go to: www.freescale.com
2
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
Bosch Controller Area Network
Version 2.0
Protocol Standard
All Trade Marks recognized. This document contains information on new products. Specifications and information herein are
subject to change without notice.
All products are sold on Motorola’s Terms & Conditions of Supply. In ordering a product covered by this document the
Customer agrees to be bound by those Terms & Conditions and nothing contained in this document constitutes or forms part
of a contract (with the exception of the contents of this Notice). A copy of Motorola’s Terms & Conditions of Supply is available
on request.
Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty,
representation or guarantee regarding the suitability of its products for any particular purpose, nor does Motorola assume any
liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including
without limitation consequential or incidental damages. “Typical” parameters can and do vary in different applications. All
operating parameters, including “Typicals”, must be validated for each customer application by customer’s technical experts.
Motorola does not convey any license under its patent rights nor the rights of others. Motorola products are not designed,
intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
intended to support or sustain life, or for any other application in which the failure of the Motorola product could create a
situation where personal injury or death may occur. Should Buyer purchase or use Motorola products for any such unintended
or unauthorized application, Buyer shall indemnify and hold Motorola and its officers, employees, subsidiaries, affiliates, and
distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly
or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim
alleges that Motorola was negligent regarding the design or manufacture of the part. Motorola and !are registered
trademarks of Motorola, Inc. Motorola, Inc. is an Equal Opportunity/Affirmative Action Employer.
The Customer should ensure that it has the most up to date version of the document by contacting its local Motorola office.
This document supersedes any earlier documentation relating to the products referred to herein. The information contained
in this document is current at the date of publication. It may subsequently be updated, revised or withdrawn.
 MOTOROLA LTD., 1998
TPG
For More Information On This Product,
Go to: www.freescale.com
3
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Conventions
Where abbreviations are used in the text, an explanation can be found in the
glossary, at the back of this manual. Register and bit mnemonics are defined in the
paragraphs describing them.
An overbar is used to designate an active-low signal, eg: RESET.
Unless otherwise stated, shaded cells in a register diagram indicate that the bit is
either unused or reserved; ‘u’ is used to indicate an undefined state (on reset).
TPG
For More Information On This Product,
Go to: www.freescale.com
3
Freescale Semiconductor, Inc.
CUSTOMER FEEDBACK QUESTIONNAIRE (CAN PROTOCOL)
Motorola wishes to continue to improve the quality of its documentation. We would welcome your feedback on the publication you
have just received. Having used the document, please complete this card (or a photocopy of it, if you prefer).
1.
How would you rate the quality of the document? Check one box in each category.
Excellent
Organization
Readability
Understandability
Illustrations
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
Excellent
❏
❏
❏
❏
❏
Tables
Table of contents
Index
Page size/binding
Overall impression
Poor
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
Comments:
2.
What is your intended use for this document? If more than one option applies, please rank them (1, 2, 3).
Selection of device for new application
System design
Training purposes
3.
❏
❏
❏
Other
❏
Please specify:
How well does this manual enable you to perform the task(s) outlined in question 2?
Completely
– Cut along this line to remove –
Freescale Semiconductor, Inc...
Accuracy
❏
❏
❏
❏
❏
Poor
Not at all
Comments:
❏ ❏ ❏ ❏
4.
How easy is it to find the information you are looking for?
Easy
Difficult
Comments:
❏ ❏ ❏ ❏
5.
Is the level of technical detail in the following sections sufficient to allow you to understand how the device functions?
Too little detail
SECTION 1
INTRODUCTION
SECTION 2
BASIC CONCEPTS
SECTION 3
MESSAGE TRANSFER
SECTION 4
ERROR HANDLING
SECTION 5
FAULT CONFINEMENT
SECTION 6
BIT TIMING REQUIREMENTS
SECTION 7
INCREASING OSCILLATOR TOLERANCE
SECTION 8
THE PHYSICAL LAYER
SECTION 9
INTRODUCTION
SECTION 10 BASIC CONCEPTS
SECTION 11 MESSAGE TRANSFER
SECTION 12 ERROR HANDLING
SECTION 13 FAULT CONFINEMENT
SECTION A
THE MOTOROLA CAN (MCAN) MODULE
SECTION B
TOUCAN
SECTION C
THE MOTOROLA SCALEABLE CAN (MSCAN08) MODULE
SECTION D
THE MOTOROLA SCALEABLE CAN (MSCAN12) MODULE
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
6.
Have you found any errors? If so, please comment:
7.
From your point of view, is anything missing from the document? If so, please say what:
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
Too much detail
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
TPG
For More Information On This Product,
Go to: www.freescale.com
4
8.
How could we improve this document?
9.
How would you rate Motorola’s documentation?
Excellent
– In general
– Against other semiconductor suppliers
✂
Freescale Semiconductor, Inc.
Poor
❏ ❏ ❏ ❏
❏ ❏ ❏ ❏
11. Which company (in any field) provides the best technical documentation?
12. How many years have you worked with microprocessors?
Less than 1 year
❏
1–3 years
❏
3–5 years
❏
More than 5 years
❏
– Second fold back along this line –
NE PAS AFFRANCHIR
By air mail
Par avion
NO STAMP REQUIRED
REPONSE PAYEE
GRANDE-BRETAGNE
Motorola Ltd.,
Colvilles Road,
Kelvin Industrial Estate,
EAST KILBRIDE,
G75 8BR.
GREAT BRITAIN.
– Cut along this line to remove –
IBRS NUMBER PHQ-B/207/G
CCRI NUMERO PHQ-B/207/G
– First fold back along this line –
Freescale Semiconductor, Inc...
10. Which semiconductor manufacturer provides the best technical documentation?
F.A.O. Technical Publications Manager
(re: BCANPSV2.0/D)
Semiconductor Products Sector
– Third fold back along this line –
13. Currently there is some discussion in the semiconductor industry regarding a move towards providing data sheets in electronic
form. If you have any opinion on this subject, please comment.
14. We would be grateful if you would supply the following information (at your discretion), or attach your card.
Name:
Phone No:
Position:
FAX No:
Department:
Company:
Address:
Thank you for helping us improve our documentation,
Technical Publications Manager, Motorola Ltd., Scotland.
TPG
For More Information On This Product,
Go
to: tuck
www.freescale.com
– Finally,
this edge into opposite flap –
5
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
TABLE OF CONTENTS
Paragraph
Number
TITLE
Page
Number
PART A
1
INTRODUCTION
2
BASIC CONCEPTS
2.1
Layered structure of a CAN node .......................................................................... 2-1
2.2
Messages .............................................................................................................. 2-1
2.2.1
Information routing........................................................................................... 2-1
2.2.1.1
System flexibility......................................................................................... 2-1
2.2.1.2
Message routing......................................................................................... 2-2
2.2.1.3
Multicast ..................................................................................................... 2-3
2.2.1.4
Data consistency........................................................................................ 2-3
2.3
Bit-rate ................................................................................................................... 2-3
2.4
Priorities ................................................................................................................ 2-3
2.5
Remote data request ............................................................................................. 2-3
2.6
Multi-master........................................................................................................... 2-3
2.7
Arbitration .............................................................................................................. 2-4
2.8
Data integrity ......................................................................................................... 2-4
2.8.1
Error detection ................................................................................................. 2-4
2.8.2
Performance of error detection ........................................................................ 2-5
2.9
Error signalling and recovery time ......................................................................... 2-5
2.10 Fault confinement .................................................................................................. 2-5
2.11 Connections........................................................................................................... 2-5
2.12 Single channel ....................................................................................................... 2-6
2.13 Bus values ............................................................................................................. 2-6
2.14 Acknowledgement ................................................................................................. 2-6
2.15 Sleep mode/wake-up............................................................................................. 2-6
CAN PROTOCOL
Rev. 3
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
i
6
Freescale Semiconductor, Inc.
Paragraph
Number
TABLE OF CONTENTS
Page
Number
Freescale Semiconductor, Inc...
3
MESSAGE TRANSFER
3.1
Definition of transmitter/receiver............................................................................ 3-1
3.1.1
Transmitter ....................................................................................................... 3-1
3.1.2
Receiver........................................................................................................... 3-1
3.2
Frame types........................................................................................................... 3-1
3.2.1
Data frame ....................................................................................................... 3-2
3.2.1.1
Start of frame ............................................................................................. 3-2
3.2.1.2
Arbitration field ........................................................................................... 3-2
3.2.1.3
Control field................................................................................................ 3-3
3.2.1.4
Data field.................................................................................................... 3-3
3.2.1.5
CRC field.................................................................................................... 3-4
3.2.1.6
ACK field .................................................................................................... 3-5
3.2.1.7
End of frame .............................................................................................. 3-6
3.2.2
Remote frame .................................................................................................. 3-6
3.2.3
Error frame....................................................................................................... 3-7
3.2.3.1
Error flag .................................................................................................... 3-7
3.2.3.2
Error Delimiter............................................................................................ 3-8
3.2.4
Overload frame ................................................................................................ 3-8
3.2.4.1
Overload flag.............................................................................................. 3-9
3.2.4.2
Overload Delimiter ..................................................................................... 3-9
3.2.5
Interframe space.............................................................................................. 3-9
3.2.5.1
INTERMISSION ......................................................................................... 3-10
3.2.5.2
Bus idle ...................................................................................................... 3-10
3.2.5.3
Suspend transmission................................................................................ 3-13
3.3
Message validation................................................................................................ 3-13
3.3.1
Transmitter ....................................................................................................... 3-13
3.3.2
Receiver........................................................................................................... 3-13
3.4
Bit-stream coding .................................................................................................. 3-13
4
ERROR HANDLING
4.1
Error detection....................................................................................................... 4-1
4.1.1
Bit error ............................................................................................................ 4-1
4.1.2
Stuff error......................................................................................................... 4-1
4.1.3
CRC error ........................................................................................................ 4-1
4.1.4
Form error........................................................................................................ 4-2
4.1.5
Acknowledgement error................................................................................... 4-2
4.2
Error signalling ...................................................................................................... 4-2
MOTOROLA
ii
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
7
Freescale Semiconductor, Inc.
Paragraph
Number
TABLE OF CONTENTS
Page
Number
5
FAULT CONFINEMENT
Freescale Semiconductor, Inc...
5.1
5.2
CAN node status ................................................................................................... 5-1
Error counts ........................................................................................................... 5-1
6
BIT TIMING REQUIREMENTS
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.8.1
6.9
6.9.1
6.9.2
6.9.3
6.9.4
6.9.5
Nominal bit rate ..................................................................................................... 6-1
Nominal bit time..................................................................................................... 6-1
SYNC_SEG ........................................................................................................... 6-2
PROP_SEG........................................................................................................... 6-2
PHASE_SEG1, PHASE_SEG2 ............................................................................. 6-2
Sample point.......................................................................................................... 6-2
Information processing time .................................................................................. 6-2
Time quantum........................................................................................................ 6-2
Length of time segments ................................................................................. 6-3
Synchronization ..................................................................................................... 6-3
Hard synchronization ....................................................................................... 6-3
Resynchronization jump width ......................................................................... 6-3
Phase error of an edge .................................................................................... 6-4
Resynchronization ........................................................................................... 6-4
Synchronization rules ...................................................................................... 6-4
7
INCREASING OSCILLATOR TOLERANCE
7.1
7.2
7.2.1
7.2.2
7.2.3
7.2.4
7.3
7.3.1
7.3.2
7.4
7.5
7.5.1
7.5.2
7.6
7.7
7.8
Protocol modifications ........................................................................................... 7-1
Determination of the maximum synchronization length......................................... 7-2
Local error, where at least two of the nodes are Error ACTIVE ....................... 7-2
Two consecutive Overload frames ................................................................... 7-3
Acknowledge error at transmitter, where all nodes are Error PASSIVE........... 7-4
Local error at transmitter, where all nodes are Error PASSIVE........................ 7-5
Bit timing................................................................................................................ 7-6
Construction of the bit timing for maximum oscillator tolerance....................... 7-6
Construction of the bit timing for maximum bit rate.......................................... 7-7
Calculation of the oscillator tolerance.................................................................... 7-8
Maximum oscillator tolerances .............................................................................. 7-9
Oscillator tolerance for existing CAN protocol.................................................. 7-9
Oscillator tolerance for enhanced CAN protocol.............................................. 7-9
Resynchronization ................................................................................................. 7-10
Compatibility of existing and enhanced CAN protocols......................................... 7-10
Assessment ........................................................................................................... 7-11
CAN PROTOCOL
Rev. 3
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
iii
8
Freescale Semiconductor, Inc.
Paragraph
Number
TABLE OF CONTENTS
Page
Number
PART B
Freescale Semiconductor, Inc...
8
INTRODUCTION
9
BASIC CONCEPTS
9.1
Layered structure of a CAN node .......................................................................... 9-1
9.2
Messages .............................................................................................................. 9-1
9.2.1
Information routing........................................................................................... 9-1
9.2.1.1
System flexibility ........................................................................................ 9-2
9.2.1.2
Message routing ........................................................................................ 9-3
9.2.1.3
Multicast..................................................................................................... 9-3
9.2.1.4
Data consistency........................................................................................ 9-3
9.3
Bit-rate................................................................................................................... 9-3
9.4
Priorities ................................................................................................................ 9-3
9.5
Remote data request............................................................................................. 9-3
9.6
Multi-master........................................................................................................... 9-4
9.7
Arbitration .............................................................................................................. 9-4
9.8
Data integrity ......................................................................................................... 9-4
9.8.1
Error detection ................................................................................................. 9-4
9.8.2
Performance of error detection ........................................................................ 9-5
9.9
Error signalling and recovery time......................................................................... 9-5
9.10 Fault confinement .................................................................................................. 9-5
9.11 Connections .......................................................................................................... 9-5
9.12 Single channel....................................................................................................... 9-6
9.13 Bus values............................................................................................................. 9-6
9.14 Acknowledgement ................................................................................................. 9-6
9.15 Sleep mode/wake-up............................................................................................. 9-6
9.16 Oscillator Tolerance ............................................................................................... 9-7
10
MESSAGE TRANSFER
10.1 Definition of transmitter/receiver.......................................................................... 10-1
10.1.1
Transmitter ..................................................................................................... 10-1
10.1.2
Receiver......................................................................................................... 10-1
10.2 Frame formats ..................................................................................................... 10-1
10.3 Frame types......................................................................................................... 10-1
10.3.1
Data frame ..................................................................................................... 10-2
10.3.1.1
Start of frame ........................................................................................... 10-2
MOTOROLA
iv
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
9
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Paragraph
Number
TABLE OF CONTENTS
Page
Number
10.3.1.2
Arbitration field ......................................................................................... 10-3
10.3.1.3
Control field .............................................................................................. 10-4
10.3.1.4
Data field .................................................................................................. 10-5
10.3.1.5
CRC field (Standard Format and Extended Format)................................ 10-6
10.3.1.6
ACK field (Standard Format and Extended Format) ................................ 10-7
10.3.1.7
End of frame............................................................................................. 10-7
10.3.2
Remote frame ................................................................................................ 10-8
10.3.3
Error frame..................................................................................................... 10-8
10.3.3.1
Error flag .................................................................................................. 10-9
10.3.3.2
Error delimiter........................................................................................... 10-9
10.3.4
Overload frame .............................................................................................. 10-10
10.3.4.1
Overload flag............................................................................................ 10-11
10.3.4.2
Overload delimiter .................................................................................... 10-11
10.3.5
Interframe space ............................................................................................ 10-11
10.3.5.1
INTERMISSION ....................................................................................... 10-12
10.3.5.2
Bus idle .................................................................................................... 10-13
10.3.5.3
Suspend transmission.............................................................................. 10-13
10.4 Conformance with regard to frame formats ......................................................... 10-13
10.5 Message filtering ................................................................................................. 10-13
10.6 Message validation.............................................................................................. 10-17
10.6.1
Transmitter ..................................................................................................... 10-17
10.6.2
Receiver......................................................................................................... 10-17
10.7 Bit-stream coding................................................................................................. 10-17
11
ERROR HANDLING
11.1 Error detection ..................................................................................................... 11-1
11.1.1
Bit error .......................................................................................................... 11-1
11.1.2
Stuff error....................................................................................................... 11-1
11.1.3
CRC error ...................................................................................................... 11-1
11.1.4
Form error ...................................................................................................... 11-2
11.1.5
Acknowledgement error ................................................................................. 11-2
11.2 Error signalling..................................................................................................... 11-2
12
FAULT CONFINEMENT
12.1
12.2
CAN node status ................................................................................................. 12-1
Error counts ......................................................................................................... 12-1
CAN PROTOCOL
Rev. 3
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
v
10
Freescale Semiconductor, Inc.
Paragraph
Number
TABLE OF CONTENTS
Page
Number
Freescale Semiconductor, Inc...
13
BIT TIMING REQUIREMENTS
13.1
13.2
13.3
13.4
13.5
13.6
13.7
13.8
13.8.1
13.9
13.9.1
13.9.2
13.9.3
13.9.4
13.9.5
Nominal bit rate ................................................................................................... 13-1
Nominal bit time................................................................................................... 13-1
SYNC_SEG......................................................................................................... 13-2
PROP_SEG......................................................................................................... 13-2
PHASE_SEG1, PHASE_SEG2........................................................................... 13-2
Sample point ....................................................................................................... 13-2
Information processing time ................................................................................ 13-2
Time quantum ..................................................................................................... 13-2
Length of time segments ............................................................................... 13-3
Synchronization................................................................................................... 13-4
Hard synchronization ..................................................................................... 13-4
Resynchronization jump width ....................................................................... 13-4
Phase error of an edge .................................................................................. 13-4
Resynchronization ......................................................................................... 13-4
Synchronization rules .................................................................................... 13-5
A
THE MOTOROLA CAN (MCAN) MODULE
A.1
Functional overview............................................................................................... A-1
A.1.1
IML – interface management logic................................................................... A-1
A.1.2
TBF – transmit buffer ....................................................................................... A-3
A.1.3
RBF – receive buffer ........................................................................................ A-3
A.1.4
BSP – bit stream processor ............................................................................. A-3
A.1.5
BTL – bit timing logic ....................................................................................... A-4
A.1.6
TCL – transceive logic ..................................................................................... A-4
A.1.7
EML – error management logic ....................................................................... A-4
A.2
MCAN interface ..................................................................................................... A-5
A.2.1
CIL – controller interface unit........................................................................... A-5
A.2.2
Address allocation ........................................................................................... A-6
A.2.3
Control registers .............................................................................................. A-7
A.2.4
MCAN control register (CCNTRL) ................................................................... A-7
A.2.5
MCAN command register (CCOM) .................................................................. A-9
A.2.6
MCAN status register (CSTAT) ........................................................................ A-11
A.2.7
MCAN interrupt register (CINT) ....................................................................... A-13
A.2.8
MCAN acceptance code register (CACC) ....................................................... A-14
A.2.9
MCAN acceptance mask register (CACM) ...................................................... A-15
A.2.10
MCAN bus timing register 0 (CBT0) ................................................................ A-15
A.2.11
MCAN bus timing register 1 (CBT1) ................................................................ A-17
A.2.12
MCAN output control register (COCNTRL) ..................................................... A-19
A.2.13
Transmit buffer identifier register (TBI)............................................................. A-21
A.2.14
Remote transmission request and data length code register (TRTDL) ........... A-22
MOTOROLA
vi
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
11
Freescale Semiconductor, Inc.
Paragraph
Number
Freescale Semiconductor, Inc...
A.2.15
A.2.16
A.2.17
A.2.18
A.2.19
TABLE OF CONTENTS
Page
Number
Transmit data segment registers (TDS) 1 – 8 ..................................................A-23
Receive buffer identifier register (RBI) .............................................................A-23
Remote transmission request and data length code register (RRTDL) ...........A-23
Receive data segment registers (RDS) 1 – 8 ..................................................A-23
Organization of buffers.....................................................................................A-25
B
TOUCAN
B.1
Introduction............................................................................................................B-1
B.2
TOUCAN module features.....................................................................................B-1
B.3
External Pins .........................................................................................................B-3
B.4
The CAN system ...................................................................................................B-3
B.5
Message buffer structure.......................................................................................B-4
B.6
Common fields to extended and standard format frames......................................B-5
B.6.1
CODE ..............................................................................................................B-5
B.6.2
LENGTH (receive mode) .................................................................................B-6
B.6.3
LENGTH (transmit mode) ................................................................................B-6
B.6.4
DATA BYTE 0..7...............................................................................................B-6
B.6.5
RESERVED .....................................................................................................B-6
B.7
Fields for extended format frames .........................................................................B-7
B.7.1
TIME STAMP ...................................................................................................B-7
B.7.2
ID[28-18, 17-15]...............................................................................................B-7
B.7.3
SRR — Substitute remote request ..................................................................B-7
B.7.4
IDE — ID Extended .........................................................................................B-7
B.7.5
ID[14-0] ............................................................................................................B-7
B.7.6
RTR — Remote transmission request .............................................................B-7
B.8
Fields for standard format frames..........................................................................B-8
B.8.1
TIME STAMP ...................................................................................................B-8
B.8.2
ID[28-18] ..........................................................................................................B-8
B.8.3
RTR — Remote transmission request .............................................................B-8
B.8.4
RTR/SRR bit treatment ....................................................................................B-8
B.9
Functional overview...............................................................................................B-8
B.10 Transmit process ...................................................................................................B-9
B.11 Receive process ....................................................................................................B-10
B.11.1
Self-received frames ........................................................................................B-11
B.12 Message buffer handling .......................................................................................B-11
B.12.1
Tx message buffer deactivation .......................................................................B-11
B.12.2
Rx message buffer deactivation.......................................................................B-11
B.13 Lock/release/BUSY mechanism and SMB usage .................................................B-12
B.14 Remote frames ......................................................................................................B-12
B.15 Overload frames ....................................................................................................B-13
B.16 Time stamp............................................................................................................B-13
B.17 Bit-timing configuration ..........................................................................................B-14
B.18 Bit-timing operation notes......................................................................................B-14
CAN PROTOCOL
Rev. 3
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
vii
12
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Paragraph
Number
Page
Number
TABLE OF CONTENTS
B.19 TOUCAN initialisation sequence ........................................................................... B-15
B.20 Special operating modes....................................................................................... B-16
B.20.1
DEBUG mode .................................................................................................. B-16
B.20.2
STOP mode ..................................................................................................... B-16
B.20.2.1
STOP mode operation notes...................................................................... B-17
B.20.3
Auto Power Save mode ................................................................................... B-18
B.20.4
Support BERR for RISC architechture (BERR_PLUG) ................................... B-19
B.20.4.1
Modular family (BERR_PLUG = 0) ............................................................ B-19
B.20.4.2
RISC family (BERR_PLUG = 1)................................................................. B-19
B.21 Interrupts ............................................................................................................... B-20
B.21.1
Modular family archtecture (IRQ_PLUG = 0)................................................... B-20
B.21.2
RISC family architecture (IRQ_PLUG = 1) ...................................................... B-22
B.22 Programmer’s model ............................................................................................. B-23
B.22.1
Programming validity ....................................................................................... B-25
B.22.2
Reserved bits................................................................................................... B-25
B.22.3
System registers .............................................................................................. B-25
B.22.4
MCR — Module configuration register............................................................. B-25
B.22.5
TCR — Test configuration register................................................................... B-29
B.22.6
ICR — Interrupt configuration register (Modular family IRQ_PLUG = 0) ......... B-29
B.22.7
ICR — Interrupt configuration register (RISC family IRQ_PLUG = 1) ............. B-30
B.23 Control registers .................................................................................................... B-31
B.23.1
CTRL0 — Control register 0 ............................................................................ B-31
B.23.2
CTRL1 — Control register 1 ............................................................................ B-32
B.23.3
PRESDIV — Prescaler divide register............................................................. B-34
B.23.4
CTRL2 — Control register 2 ............................................................................ B-34
B.23.5
TIMER — Free running timer........................................................................... B-35
B.24 Rx mask registers.................................................................................................. B-35
B.24.1
RXMASK — Rx global mask register .............................................................. B-36
B.24.2
RX14MASK — Rx buffer 14 mask................................................................... B-37
B.24.3
RX15MASK — Rx buffer 15 mask................................................................... B-37
B.25 Global information registers .................................................................................. B-38
B.25.1
STATH, STATL — Error and status report registers ......................................... B-38
B.25.2
IMASKH, IMASKL— Interrupt mask registers ................................................. B-41
B.25.3
IFLAGH, IFLAGL — Interrupt flag registers..................................................... B-41
B.25.4
Error counters .................................................................................................. B-42
C
THE MOTOROLA SCALEABLE CAN (MSCAN08) MODULE
C.1
Features ................................................................................................................C-1
C.2
External Pins .........................................................................................................C-3
C.3
Message Storage ..................................................................................................C-4
C.3.1
Background......................................................................................................C-4
C.3.2
Receive Structures ..........................................................................................C-5
C.3.3
Transmit Structures..........................................................................................C-7
MOTOROLA
viii
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
13
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Paragraph
Number
TABLE OF CONTENTS
Page
Number
C.4
Identifier acceptance Filter ....................................................................................C-8
C.5
Interrupts ...............................................................................................................C-11
C.5.1
Interrupt Acknowledge .....................................................................................C-11
C.5.2
Interrupt Vectors...............................................................................................C-12
C.6
Protocol Violation Protection..................................................................................C-12
C.7
Low Power Modes .................................................................................................C-13
C.7.1
MSCAN08 Internal Sleep Mode.......................................................................C-13
C.7.2
MSCAN08 Soft Reset Mode ............................................................................C-15
C.7.3
MSCAN08 Power Down Mode.........................................................................C-15
C.7.4
CPU Wait Mode ...............................................................................................C-15
C.7.5
Programmable Wake-Up Function ...................................................................C-15
C.8
Timer Link..............................................................................................................C-16
C.9
Clock System.........................................................................................................C-16
C.10 Memory Map .........................................................................................................C-19
C.11 Programmer’s Model of message storage.............................................................C-20
C.11.1
Message Buffer Outline ...................................................................................C-20
C.11.2
Identifier Registers (IDRn) ...............................................................................C-21
C.11.3
Data Length Register (DLR) ............................................................................C-22
C.11.4
Data Segment Registers (DSRn).....................................................................C-23
C.11.5
Transmit Buffer Priority Registers (TBPR) .......................................................C-23
C.12 Programmer’s Model of Control Registers.............................................................C-24
C.12.1
Overview ..........................................................................................................C-24
C.12.2
MSCAN08 Module Control Register (CMCR0)................................................C-25
C.12.3
MSCAN08 Module Control Register (CMCR1)................................................C-26
C.12.4
MSCAN08 Bus Timing Register 0 (CBTR0) ....................................................C-27
C.12.5
MSCAN08 Bus Timing Register 1 (CBTR1) ....................................................C-28
C.12.6
MSCAN08 Receiver Flag Register (CRFLG)...................................................C-29
C.12.7
MSCAN08 Receiver Interrupt Enable Register (CRIER) .................................C-31
C.12.8
MSCAN08 Transmitter Flag Register (CTFLG)................................................C-33
C.12.9
MSCAN08 Transmitter Control Register (CTCR) .............................................C-34
C.12.10 MSCAN08 Identifier Acceptance Control Register (CIDAC) ............................C-35
C.12.11 MSCAN08 Receive Error Counter (CRXERR).................................................C-36
C.12.12 MSCAN08 Transmit Error Counter (CTXERR).................................................C-36
C.12.13 MSCAN08 Identifier Acceptance Registers (CIDAR0-3) .................................C-37
C.12.14 MSCAN08 Identifier Mask Registers (CIDMR0-3)...........................................C-38
D
THE MOTOROLA SCALEABLE CAN (MSCAN12) MODULE
D.1
Features ................................................................................................................D-1
D.2
External Pins .........................................................................................................D-2
D.3
Message Storage ..................................................................................................D-4
D.3.1
Background......................................................................................................D-4
D.3.2
Receive Structures ..........................................................................................D-5
D.3.3
Transmit Structures ..........................................................................................D-7
CAN PROTOCOL
Rev. 3
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
ix
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Paragraph
Number
TABLE OF CONTENTS
Page
Number
D.4
Identifier Acceptance Filter....................................................................................D-8
D.5
Interrupts ...............................................................................................................D-11
D.5.1
Interrupt Acknowledge .....................................................................................D-11
D.5.2
Interrupt Vectors ..............................................................................................D-12
D.6
Protocol Violation Protection .................................................................................D-12
D.7
Low Power Modes .................................................................................................D-13
D.7.1
MSCAN12 Sleep Mode ...................................................................................D-14
D.7.2
MSCAN12 Soft Reset Mode ............................................................................D-15
D.7.3
MSCAN12 Power Down Mode.........................................................................D-15
D.7.4
Programmable Wake-Up Function...................................................................D-15
D.8
Timer Link..............................................................................................................D-16
D.9
Clock System ........................................................................................................D-16
D.10 Memory Map .........................................................................................................D-19
D.11 Programmer’s Model of Message Storage ............................................................D-20
D.11.1
Message Buffer Outline ...................................................................................D-20
D.11.2
Identifier Registers (IDRn) ...............................................................................D-22
D.11.3
Data Length Register (DLR) ............................................................................D-23
D.11.4
Data Segment Registers (DSRn) ....................................................................D-23
D.11.5
Transmit Buffer Priority Registers (TBPR) .......................................................D-24
D.12 Programmer’s Model of Control Registers ............................................................D-24
D.12.1
Overview..........................................................................................................D-24
D.12.2
MSCAN12 Module Control Register 0 (CMCR0).............................................D-26
D.12.3
MSCAN12 Module Control Register 1 (CMCR1).............................................D-27
D.12.4
MSCAN12 Bus Timing Register 0 (CBTR0) ....................................................D-28
D.12.5
MSCAN12 Bus Timing Register 1 (CBTR1) ....................................................D-29
D.12.6
MSCAN12 Receiver Flag Register (CRFLG)...................................................D-31
D.12.7
MSCAN12 Receiver Interrupt Enable Register (CRIER) .................................D-33
D.12.8
MSCAN12 Transmitter Flag Register (CTFLG)................................................D-34
D.12.9
MSCAN12 Transmitter Control Register (CTCR).............................................D-35
D.12.10 MSCAN12 Identifier Acceptance Control Register (CIDAC)............................D-36
D.12.11 MSCAN12 Receive Error Counter (CRXERR) ................................................D-37
D.12.12 MSCAN12 Transmit Error Counter (CTXERR) ................................................D-37
D.12.13 MSCAN12 Identifier Acceptance Registers (CIDAR0-7) .................................D-37
D.12.14 MSCAN12 Identifier Mask Registers (CIDMR0-7)...........................................D-38
D.12.15 MSCAN12 Port CAN Control Register (PCTLCAN) ........................................D-39
D.12.16 MSCAN12 Port CAN Data Register (PORTCAN)............................................D-40
D.12.17 MSCAN12 Port CAN Data Direction Register (DDRCAN)...............................D-40
GLOSSARY
INDEX
MOTOROLA
x
TABLE OF CONTENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
Freescale Semiconductor, Inc.
—this line does not form part of the document—
CANLOF
[email protected]:06
Freescale Semiconductor, Inc...
LIST OF FIGURES
Figure
Number
2-1
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
3-11
6-1
7-1
7-2
7-3
7-4
7-5
7-6
9-1
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
TITLE
Page
Number
CAN layers ............................................................................................................. 2-2
Data frame.............................................................................................................. 3-2
Arbitration field ....................................................................................................... 3-2
Control field ............................................................................................................ 3-3
CRC field ................................................................................................................ 3-4
ACK field ................................................................................................................ 3-5
Remote frame......................................................................................................... 3-6
Error frame ............................................................................................................. 3-7
Overload frame....................................................................................................... 3-8
Interframe space (1) ............................................................................................... 3-10
Interframe space (2) ............................................................................................... 3-10
CAN frame formats................................................................................................. 3-11
Nominal bit time...................................................................................................... 6-1
Local error .............................................................................................................. 7-2
Two consecutive Overload frames.......................................................................... 7-3
Acknowledge error at transmitter, all nodes Error PASSIVE .................................. 7-4
Local error at transmitter, all nodes Error PASSIVE ............................................... 7-5
Bit timing for maximum oscillator tolerance ............................................................ 7-6
Bit timing for maximum bit rate ............................................................................... 7-7
CAN layers ............................................................................................................. 9-2
Data frame............................................................................................................ 10-2
Arbitration field; Standard Format......................................................................... 10-3
Arbitration field; Extended Format ........................................................................ 10-3
Control field; Standard Format and Extended Format.......................................... 10-5
CRC field .............................................................................................................. 10-6
ACK field .............................................................................................................. 10-7
Remote frame....................................................................................................... 10-8
Error frame ........................................................................................................... 10-9
Overload frame..................................................................................................... 10-10
Interframe space (1) ............................................................................................. 10-12
Interframe space (2) ............................................................................................. 10-12
CAN frame format - Standard Format .................................................................. 10-14
CAN frame format - Extended Format.................................................................. 10-16
CAN PROTOCOL
Rev. 3
LIST OF FIGURES
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
xi
14
Freescale Semiconductor, Inc.
[email protected]:06
Freescale Semiconductor, Inc...
Figure
Number
13-1
13-2
A-1
A-2
A-3
A-4
A-5
A-6
B-1
B-2
B-3
B-4
B-6
C-1
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9
C-10
D-1
D-2
D-3
D-4
D-5
D-6
D-7
D-8
D-9
D-10
D-11
D-12
D-13
D-14
D-15
—this line does not form part of the document—
CANLOF
TITLE
Page
Number
Nominal bit time ....................................................................................................13-1
Bit timing of CAN devices without local CPU ........................................................13-3
MCAN module block diagram................................................................................. A-2
Block diagram of the MCAN interface .................................................................... A-5
MCAN module memory map.................................................................................. A-6
Oscillator block diagram ......................................................................................... A-16
Segments within the bit time .................................................................................. A-17
A typical physical interface between the MCAN and the MCAN bus lines ............. A-24
TOUCAN block diagram and pinout ....................................................................... B-2
Typical CAN system ............................................................................................... B-3
Message buffer structure........................................................................................ B-4
TOUCAN interrupt vector generation ..................................................................... B-20
Int request multiplex timing..................................................................................... B-22
The CAN System ................................................................................................... C-3
User Model for Message Buffer Organization ........................................................ C-6
Single 32 bit Maskable Identifier Acceptance Filter ............................................... C-8
Dual 16 bit Maskable Acceptance Filters ............................................................... C-9
Quadruple 8 bit Maskable Acceptance Filters........................................................ C-10
Sleep Request / Acknowledge Cycle ..................................................................... C-14
Clocking Scheme ................................................................................................... C-17
Segments within the Bit Time................................................................................. C-18
Receive/transmit message buffer extended identifier registers.............................. C-21
Standard identifier mapping registers .................................................................... C-22
The CAN System ................................................................................................... D-3
User model for message buffer organisation.......................................................... D-6
32-bit Maskable Identifier Acceptance Filter .......................................................... D-8
16-bit Maskable Acceptance Filters ....................................................................... D-9
8-bit Maskable Acceptance Filters ......................................................................... D-10
Sleep Request / Acknowledge Cycle ..................................................................... D-14
Clocking Scheme ................................................................................................... D-17
Segments within the Bit Time................................................................................. D-18
MSCAN12 Memory Map ........................................................................................ D-19
Receive/transmit message buffer extended identifier............................................. D-21
Standard identifier mapping ................................................................................... D-21
Identifier acceptance registers (1ST bank) ............................................................. D-38
Identifier acceptance registers (2ND bank)............................................................. D-38
Identifier mask registers (1ST bank) ....................................................................... D-38
Identifier mask registers (2NDbank)........................................................................ D-39
MOTOROLA
xii
LIST OF FIGURES
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
15
Freescale Semiconductor, Inc.
—this line does not form part of the document—
CANLOT
[email protected]:07
Freescale Semiconductor, Inc...
LIST OF TABLES
Table
Number
3-1
10-1
A-1
A-2
A-3
A-4
A-5
A-6
A-7
1-8
B-1
B-2
B-3
B-4
B-5
B-6
B-7
B-8
B-9
B-10
B-11
C-1
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9
C-10
C-11
C-12
TITLE
Page
Number
Data length coding ................................................................................................. 3-4
Data length coding ............................................................................................... 10-5
Control registers ..................................................................................................... A-7
Synchronization jump width.................................................................................... A-16
Baud rate prescaler ................................................................................................ A-16
Time segment values ............................................................................................. A-18
Output control modes ............................................................................................. A-19
MCAN driver output levels...................................................................................... A-21
Data length codes .................................................................................................. A-22
MCAN data buffers ................................................................................................. A-25
Message buffer code for Rx buffers........................................................................ B-5
Message buffer code for Tx buffers ........................................................................ B-5
Examples of system clock/CAN bit-rate/SCLOCK.................................................. B-14
Interrupt priorities and vector addresses ................................................................ B-21
Interrupt levels ........................................................................................................ B-22
TOUCAN memory map .......................................................................................... B-24
Interrupt levels ........................................................................................................ B-30
Configuration control of Tx0, Tx1 pins .................................................................... B-32
Mask examples for normal/extended messages .................................................... B-36
Bit error status ........................................................................................................ B-38
Fault confinement sate of TOUCAN ....................................................................... B-40
MSCAN08 Interrupt Vectors ................................................................................... C-12
MSCAN08 vs. CPU operating modes..................................................................... C-13
CAN Standard Compliant Bit Time Segment Settings............................................ C-18
MSCAN08 Memory Map ........................................................................................ C-19
Message Buffer Organisation ................................................................................. C-20
Data length codes .................................................................................................. C-22
MSCAN08 Control register structure...................................................................... C-24
Synchronization jump width.................................................................................... C-27
Baud rate prescaler ................................................................................................ C-27
Time segment syntax ............................................................................................. C-28
Time segment values ............................................................................................. C-29
Identifier Acceptance Mode Settings...................................................................... C-35
CAN PROTOCOL
Rev. 3
LIST OF TABLES
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
xiii
16
Freescale Semiconductor, Inc.
[email protected]:07
Freescale Semiconductor, Inc...
Table
Number
C-13
D-1
D-2
D-3
D-4
D-5
D-6
D-7
D-8
D-9
D-10
D-11
D-12
—this line does not form part of the document—
CANLOT
TITLE
Page
Number
Identifier Acceptance Hit Indication........................................................................ C-35
MSCAN12 Interrupt Vectors ................................................................................... D-12
MSCAN12 vs. CPU operating modes..................................................................... D-13
CAN Standard Compliant Bit Time Segment Settings ........................................... D-18
Message Buffer Organisation................................................................................. D-20
Data length codes .................................................................................................. D-23
MSCAN12 Control Register Structure.................................................................... D-25
Synchronization jump width ................................................................................... D-28
Baud rate prescaler................................................................................................ D-29
Time segment syntax ............................................................................................. D-30
Time segment values ............................................................................................. D-30
Identifier Acceptance Mode Settings...................................................................... D-36
Identifier Acceptance Hit Indication........................................................................ D-36
MOTOROLA
xiv
LIST OF TABLES
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
17
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
PREFACE
The Controller Area Network (CAN) Specification 2.0, as defined by BOSCH Gmbh, consists of
two parts, A and B, as follows:
•
Part A describes the CAN message format as defined in CAN Specification 1.2
•
Part B describes both standard and extended message formats
This publication covers both Part A and Part B of CAN Specification 2.0.
The standard format, as originally defined, provided 11 identifier bits. The extended format,
provides a larger address range defined by 29 bits. Users of CAN who do not need the extended
format can continue to use the original 11 bit identifier range. CAN implementations that are
designed according to Part A of this specification, or according to previous CAN specifications,
may communicate with CAN implementations that are designed according to Part B of this
specification so long as the Extended Format is not used.
TPG
CAN PROTOCOL
Rev. 3
PREFACE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
18
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
THIS PAGE LEFT BLANK INTENTIONALLY
TPG
MOTOROLA
PREFACE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
19
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
BOSCH
CONTROLLER AREA NETWORK (CAN)
VERSION 2.0
PART A
TPG
CAN PROTOCOL
Rev. 3
BOSCH CONTROLLER AREA NETWORK (CAN)
For More Information
This
VERSION 2.0 On
PART
A Product,
Go to: www.freescale.com
MOTOROLA
20
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
THIS PAGE LEFT BLANK INTENTIONALLY
TPG
MOTOROLA
BOSCH CONTROLLER AREA NETWORK (CAN)
CAN PROTOCOL
For MoreVERSION
Information
OnA This Product,
2.0 PART
Rev. 3
Go to: www.freescale.com
21
Freescale Semiconductor, Inc.
1
Freescale Semiconductor, Inc...
1
INTRODUCTION
The Controller Area Network (CAN) is a serial communications protocol that efficiently supports
distributed real-time control with a very high level of data integrity.
Though conceived and defined by BOSCH in Germany for automotive applications, CAN is not
restricted to that industry. CAN fulfils the communication needs of a wide range of applications,
from high-speed networks to low-cost multiplex wiring.
For example, in automotive electronics, engine control units, sensors and anti-skid systems may
be connected using CAN, with bit-rates up to 1 Mbit/s. At the same time, it is cost effective to build
CAN into vehicle body electronics, such as lamp clusters and electric windows, to replace the
wiring harness otherwise required.
The intention of the CAN specification is to achieve compatibility between any two CAN
implementations. Compatibility, however, has different aspects with respect to, for example,
electrical features and the interpretation of data to be transferred.
To achieve design transparency and implementation flexibility CAN has been subdivided into three
layers:
•
The Object Layer
•
The Transfer Layer
•
The Physical Layer
The Object Layer and the Transfer Layer comprise all services and functions of the data link layer
defined by the ISO/OSI model.
The scope of the Object Layer includes: determining which messages are to be transmitted;
deciding which messages received by the Transfer Layer are actually to be used; and, providing
an interface to the Application Layer related hardware. There is considerable freedom in defining
object handling.
The Transfer Layer is principally concerned with the transfer protocol, i.e. controlling the framing,
performing arbitration, error checking, error signalling and fault confinement. Within the Transfer
Layer it is decided whether the bus is free for starting a new transmission, or whether reception of
a message is just starting. Also, some general features of the bit-timing are regarded as part of the
Transfer Layer. Modifications to the Transfer Layer cannot be made.
TPG
CAN PROTOCOL
Rev. 3
INTRODUCTION
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
1-1
22
Freescale Semiconductor, Inc.
1
The Physical Layer covers the actual transfer of the bits between the different nodes, with respect
to all electrical properties. Within a network the physical layer has to be the same for all nodes.
However, there are many possible implementations of the Physical Layer.
Freescale Semiconductor, Inc...
The remainder of this document is principally concerned with the definition of the Transfer Layer,
and the consequences of the CAN protocol for the surrounding layers.
TPG
MOTOROLA
1-2
INTRODUCTION
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
23
Freescale Semiconductor, Inc.
2
Freescale Semiconductor, Inc...
2
BASIC CONCEPTS
2.1
Layered structure of a CAN node
The Object Layer is concerned with message filtering as well as status and message handling.
The Transfer Layer represents the kernel of the CAN protocol. It presents messages received to
the Object Layer and accepts messages to be transmitted by the Object Layer. The Transfer Layer
is responsible for bit timing and synchronization, message framing, arbitration, acknowledgement,
error detection and signalling, and fault confinement.
The Physical Layer defines how signals are actually transmitted. The Physical Layer is not defined
here, as it will vary according to the requirements of individual applications (for example,
transmission medium and signal level implementations).
2.2
Messages
Information on the bus is sent in fixed format messages of different but limited length (see
Section 3). When the bus is free, any connected node may start to transmit a new message.
2.2.1
Information routing
In CAN systems a node does not make use of any information about the system configuration (e.g.
node addresses). This has several important consequences, which are described below.
2.2.1.1
System flexibility
Nodes may be added to the CAN network without requiring any change in the software or
hardware of any node or the application layer.
CAN PROTOCOL
Rev. 3
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
2-1
24
Freescale Semiconductor, Inc.
2
APPLICATION LAYER
Freescale Semiconductor, Inc...
CAN LAYERS
OBJECT
Message Filtering
Message and Status Handling
TRANSFER
Fault ConÞnement
Error Detection and Signalling
Message Validation
Acknowledgement
Arbitration
Message Framing
Transfer Rate and Timing
PHYSICAL
Signal Level and Bit Representation
Transmission Medium
CAN Network
Figure 2-1
2.2.1.2
CAN layers
Message routing
The content of a message is described by an Identifier. The Identifier does not indicate the
destination of the message, but describes the meaning of the data, so that all nodes in the network
are able to decide by Message filtering whether the data is to be acted upon by them or not.
MOTOROLA
2-2
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
25
Freescale Semiconductor, Inc.
2.2.1.3
Multicast
As a consequence of the concept of Message filtering any number of nodes may receive and act
simultaneously upon the same message.
Freescale Semiconductor, Inc...
2.2.1.4
2
Data consistency
Within a CAN network it is guaranteed that a message is accepted simultaneously either by all
nodes or by no node. Thus data consistency is a property of the system achieved by the concepts
of multicast and by error handling.
2.3
Bit-rate
The speed of CAN may be different in different systems. However, in a given system the bit-rate is
uniform and fixed.
2.4
Priorities
The Identifier defines a static message priority during bus access.
2.5
Remote data request
By sending a Remote frame a node requiring data may request another node to send the
corresponding Data frame. The Data frame and the corresponding Remote frame have the same
Identifier.
2.6
Multi-master
When the bus is free any node may start to transmit a message. The node with the message of
highest priority to be transmitted gains bus access.
CAN PROTOCOL
Rev. 3
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
2-3
26
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
2
2.7
Arbitration
Whenever the bus is free, any node may start to transmit a message. If two or more nodes start
transmitting messages at the same time, the bus access conflict is resolved by bit-wise arbitration
using the Identifier. The mechanism of arbitration guarantees that neither information nor time is
lost. If a Data frame and a Remote frame with the same Identifier are initiated at the same time,
the Data frame prevails over the Remote frame. During arbitration every transmitter compares the
level of the bit transmitted with the level that is monitored on the bus. If these levels are equal the
node may continue to send. When a recessive level is sent, but a dominant level is monitored (see
Section 2.13), the node has lost arbitration and must withdraw without sending any further bits.
2.8
Data integrity
In order to achieve a very high integrity of data transfer, powerful measures of error detection,
signalling and self-checking are implemented in every CAN node.
2.8.1
Error detection
To detect errors the following measures have been taken:
•
Monitoring (each transmitter compares the bit levels detected on the bus with the bit levels
being transmitted)
•
Cyclic Redundancy Check (CRC)
•
Bit-Stuffing
•
Message Frame Check
MOTOROLA
2-4
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
27
Freescale Semiconductor, Inc.
2.8.2
Performance of error detection
2
The error detection mechanisms have the following properties:
Freescale Semiconductor, Inc...
•
•
Monitoring:
–
All global errors are detected
–
All local errors at transmitters are detected
CRC:
–
Up to 5 randomly transmitted errors within a sequence are detected
–
Burst errors of length less than 15 in a message are detected
–
Errors of any odd number of bits in a message are detected
The total residual error probability of undetected corrupted messages is less than 4.7 x 10-11.
2.9
Error signalling and recovery time
Corrupted messages are flagged by any node detecting an error. Such messages are aborted and
are retransmitted automatically. The recovery time from detecting an error until the start of the next
message is at most 29 bit times, provided there is no further error.
2.10
Fault confinement
CAN nodes are able to distinguish between short disturbances and permanent failures. Defective
nodes are switched off.
2.11
Connections
The CAN serial communication link is a bus to which a number of nodes may be connected. This
number has no theoretical limit. Practically, the total number of nodes will be limited by delay times
and/or electrical loads on the bus line.
CAN PROTOCOL
Rev. 3
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
2-5
28
Freescale Semiconductor, Inc.
2
2.12
Single channel
Freescale Semiconductor, Inc...
The bus consists of a single bidirectional channel that carries bits. From this data,
resynchronization information can be derived. The way in which this channel is implemented is not
fixed in this specification, e.g. single wire (plus ground), two differential wires, optical fibres, etc.
2.13
Bus values
The bus can have one of two complementary values: dominant or recessive. During simultaneous
transmission of dominant and recessive bits, the resulting bus value will be dominant. For example,
in the case of a wired-AND implementation of the bus, the dominant level would be represented
by a logical ‘0’ and the recessive level by a logical ‘1’.
Physical states (e.g. electrical voltage, light) that represent the logical levels are not given in this
specification.
2.14
Acknowledgement
All receivers check the consistency of the message being received and will acknowledge a
consistent message and flag an inconsistent message.
2.15
Sleep mode/wake-up
To reduce the system’s power consumption, a CAN device may be set into sleep mode, in which
there is no internal activity and the bus drivers are disconnected. The sleep mode is finished with
a wake-up by any bus activity or by internal conditions of the system. On wake-up, the internal
activity is restarted, although the transfer layer will wait for the system’s oscillator to stabilize and
then wait until it has synchronized itself to the bus activity (by checking for eleven consecutive
recessive bits), before the bus drivers are set to the ‘on-bus’ state again. In order to wake up other
sleeping nodes on the network, a special wake-up message with the dedicated, lowest possible
Identifier (rrr rrrd rrrr; r=recessive, d=dominant) may be used.
MOTOROLA
2-6
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
29
Freescale Semiconductor, Inc.
3
Freescale Semiconductor, Inc...
3
MESSAGE TRANSFER
3.1
Definition of transmitter/receiver
3.1.1
Transmitter
A node originating a message is called the TRANSMITTER of that message. The node continues
to be TRANSMITTER until the bus is idle or the node loses ARBITRATION.
3.1.2
Receiver
A node is called the RECEIVER of a message if it is not the TRANSMITTER of that message, and
the bus is not idle.
3.2
Frame types
Message transfer is manifested and controlled by four different frame types:
•
A Data frame carries data from a transmitter to the receivers.
•
A Remote frame is transmitted by a bus node to request the transmission of the Data frame
with the same Identifier.
•
An Error frame is transmitted by any node on detecting a bus error.
•
An Overload frame is used to provide for an extra delay between the preceding and the
succeeding Data or Remote frames.
Data frames and Remote frames are separated from preceding frames by an Interframe space.
Figure 3-11 at the end of this section summarizes all the frame formats.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
3-1
30
Freescale Semiconductor, Inc.
3.2.1
3
Data frame
A Data frame is composed of seven different bit fields: Start of frame, Arbitration field, Control field,
Data field, CRC field, ACK field, End of frame. The Data field can be of length zero.
Freescale Semiconductor, Inc...
Interframe
space
Interframe
space or
Overload
frame
Data frame
Start of Arbitration Control
frame
field
field
Data
field
CRC ACK End of
field field frame
Figure 3-1 Data frame
3.2.1.1
Start of frame
Start of frame marks the beginning of Data frames and Remote frames. It consists of a single
dominant bit.
A node is only allowed to start transmission when the bus is idle (see Section 3.2.5.2). All nodes
have to synchronize to the leading edge caused by Start of frame(see Section 6.9.1) of the node
starting transmission first.
3.2.1.2
Arbitration field
The Arbitration field consists of the Identifier and the RTR bit.
Interframe
space
Control
field
Arbitration field
Start of frame
Identifier
RTR bit
Figure 3-2 Arbitration field
MOTOROLA
3-2
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
31
Freescale Semiconductor, Inc.
Identifier
The Identifier’s length is 11 bits. These bits are transmitted in the order from ID10 to ID0. The least
significant bit is ID0. The 7 most significant bits must not be all recessive.
RTR bit (Remote transmission request bit)
3
Freescale Semiconductor, Inc...
In Data frames the RTR bit must be dominant. Within a Remote frame the RTR bit must be
recessive.
3.2.1.3
Control field
The Control field consists of six bits. It includes the Data length code and two bits reserved for
future expansion. The reserved bits must be sent as dominant. Receivers accept dominant and
recessive bits in all combinations.
Arbitration
field
Data field
or CRC field
Control field
r1
r0
DLC3
Reserved bits
DLC2
DLC1
DLC0
Data length code
Figure 3-3
Control field
DATA Length Code
The number of bytes in the Data field is indicated by the Data length code. This Data length code
is 4 bits wide and is transmitted within the Control field. The DLC bits can code data lengths from
0 to 8 bytes; other values are not permitted.
3.2.1.4
Data field
The Data field consists of the data to be transferred within a Data frame. It can contain from 0 to
8 bytes, each of which contain 8 bits which are transferred MSB first.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
3-3
32
Freescale Semiconductor, Inc.
Table 3-1 Data length coding
Freescale Semiconductor, Inc...
3
DLC3
d
d
d
d
d
d
d
d
r
3.2.1.5
DATA LENGTH CODE
DATABYTE
COUNT
DLC2
DLC1
DLC0
d
d
d
0
d
d
r
1
d
r
d
2
d
r
r
3
r
d
d
4
r
d
r
5
r
r
d
6
r
r
r
7
d
d
d
8
d = Òdominant
r = ÒrecessiveÓ
CRC field
The CRC field contains the CRC Sequence followed by a CRC Delimiter.
Data or
Control field
ACK
field
CRC field
CRC Sequence
CRC Delimiter
Figure 3-4 CRC field
CRC Sequence
The frame check sequence is derived from a cyclic redundancy code best suited to frames with bit
counts less than 127 bits (BCH code).
In order to carry out the CRC calculation the polynomial to be divided is defined as the polynomial
whose coefficients are given by the destuffed bit-stream consisting of Start of frame, Arbitration
field, Control field, Data field(if present) and, for the 15 lowest coefficients, by 0. This polynomial
is divided (the coefficients are calculated modulo-2) by the generator-polynomial:
X15 + X14 + X10 + X8 + X7 + X4 + X3 + 1
The remainder of this polynomial division is the CRC Sequence transmitted over the bus.
MOTOROLA
3-4
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
33
Freescale Semiconductor, Inc.
In order to implement this function, a 15-bit shift register CRC_RG(14:0) can be used. If NXTBIT
denotes the next bit of the bit-stream, given by the destuffed bit sequence from Start of frame until
the end of the Data field, the CRC Sequence is calculated as follows:
Freescale Semiconductor, Inc...
3
CRC_RG = 0
//initialize shift register
REPEAT
CRCNXT = NXTBIT EXOR CRC_RG(14)
CRC_RG(14:1) = CRC_RG(13:0)
//shift left by...
CRC_RG(0) = 0
//...one position
IF CRCNXT THEN
CRC_RG(14:0) = CRC_RG(14:0) EXOR (4599 hex)
ENDIF
UNTIL (CRC SEQUENCE starts or there is an ERROR condition)
After the transmission/reception of the last bit of the Data field, CRC_RG(14:0) contains the CRC
Sequence.
CRC Delimiter
The CRC Sequence is followed by the CRC Delimiter which consists of a single recessive bit.
3.2.1.6
ACK field
The ACK field is two bits long and contains the ACK Slot and the ACK Delimiter. In the ACK field
the transmitting node sends two recessive bits.
A RECEIVER which has received a valid message correctly reports this to the TRANSMITTER by
sending a dominant bit during the ACK Slot (i.e. it sends ACK).
CRC
field
ACK field
ACK Slot
End of
frame
ACK Delimiter
Figure 3-5 ACK field
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
3-5
34
Freescale Semiconductor, Inc.
ACK Slot
3
All nodes having received the matching CRC Sequence report this within the ACK Slot by
overwriting the recessive bit of the TRANSMITTER by a dominant bit.
ACK Delimiter
Freescale Semiconductor, Inc...
The ACK Delimiter is the second bit of the ACK field and has to be a recessive bit. As a
consequence, the ACK Slot is surrounded by two recessive bits (CRC Delimiter, ACK Delimiter).
3.2.1.7
End of frame
Each Data frame and Remote frame is delimited by a flag sequence consisting of seven recessive
bits.
3.2.2
Remote frame
A node acting as a RECEIVER for certain data can stimulate the relevant source node to transmit
the data by sending a Remote frame.
A Remote frame is composed of six different bit fields: Start of frame, Arbitration field, Control field,
CRC field, ACK field, End of frame.
The RTR bit of a Remote frame is always recessive (cf. Data frames where the RTR bit is
dominant).
There is no Data field in a Remote frame, irrespective of the value of the Data length code which
is that of the corresponding Data frame and may be assigned any value within the admissible
range 0... 8.
Interframe
space
Interframe
space or
Overload
frame
Remote frame
Start of
frame
Arbitration
field
Control
field
CRC
field
ACK
field
End of
frame
Figure 3-6 Remote frame
The polarity of the RTR bit indicates whether a transmitted frame is a Data frame (RTR bit
dominant) or a Remote frame(RTR bit recessive).
MOTOROLA
3-6
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
35
Freescale Semiconductor, Inc.
3.2.3
Error frame
The Error frame consists of two distinct fields. The first field is given by the superposition of Error
flags contributed from different nodes. The second field is the Error delimiter.
Freescale Semiconductor, Inc...
Data
frame
Interframe space
or
Overload frame
Error frame
Error flag
3
Error Delimiter
Superposition of
Error flags
Figure 3-7 Error frame
In order to terminate an Error frame correctly, an error-passive node may need the bus to be
bus-idle for at least three bit times (if there is a local error at an error-passive receiver). Therefore
the bus should not be loaded to 100%.
3.2.3.1
Error flag
There are two forms of error flag: an ACTIVE Error flag and a PASSIVE Error flag.
1) ACTIVE Error flag consists of six consecutive dominant bits.
2) The PASSIVE Error flag consists of six consecutive recessive bits unless it
is overwritten by dominant bits from other nodes.
An error-active node detecting an error condition signals this by the transmission of an ACTIVE
Error flag. The Error flag’s form violates the law of bit stuffing (see Section 3.4), applied to all fields
from Start of frame to CRC Delimiter, or destroys the fixed form ACK field or End of frame field. As
a consequence, all other nodes detect an error condition and each starts to transmit an Error flag.
So the sequence of dominant bits which actually can be monitored on the bus results from a
superposition of different Error flags transmitted by individual nodes. The total length of this
sequence varies between a minimum of six and a maximum of twelve bits.
An error-passive node detecting an error condition tries to signal this by transmitting a PASSIVE
Error flag. The error-passive node waits for six consecutive bits of equal polarity, beginning at the
start of the PASSIVE Error flag. The PASSIVE Error flag is complete when these six equal bits have
been detected.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
3-7
36
Freescale Semiconductor, Inc.
3.2.3.2
Freescale Semiconductor, Inc...
3
Error Delimiter
The Error Delimiter consists of eight recessive bits.
After transmission of an Error flag each node sends recessive bits and monitors the bus until it
detects a recessive bit. Afterwards it starts transmitting seven more recessive bits.
3.2.4
Overload frame
The Overload frame contains two bit fields, Overload flag and Overload Delimiter.
There are two kinds of Overload condition, both of which lead to the transmission of an Overload
flag:
1) Where the internal conditions of a receiver are such that the receiver
requires a delay of the next Data frameor Remote frame,
2) On detection of a dominant bit during INTERMISSION.
An Overload frame resulting from Overload condition 1 is only allowed to start at the first bit time
of an expected INTERMISSION, whereas an Overload frame resulting from Overload condition 2
starts one bit after detecting the dominant bit.
End of frame or
Error Delimiter or
Overload Delimiter
Interframe space
or
Overload frame
Overload frame
Overload flag
Overload Delimiter
Superposition of
Overload flags
Figure 3-8 Overload frame
At most, two Overload frames may be generated to delay the next Data frame or Remote frame.
MOTOROLA
3-8
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
37
Freescale Semiconductor, Inc.
3.2.4.1
Overload flag
Freescale Semiconductor, Inc...
The Overload flag consists of six dominant bits. The overall form corresponds to that of the ACTIVE
Error flag.
The Overload flag’s form destroys the fixed form of the INTERMISSION field. As a consequence,
all other nodes also detect an Overload condition and each starts to transmit an Overload flag. (In
the event that there is a dominant bit detected during the third bit of INTERMISSION locally at
some node, the other nodes will not interpret the Overload flag correctly, but interpret the first of
these six dominant bits as Start of frame. The sixth dominant bit violates the rule of bit stuffing,
thereby causing an error condition.)
3.2.4.2
3
Overload Delimiter
The Overload Delimiter consists of eight recessive bits.
The Overload Delimiter is of the same form as the Error Delimiter. After transmission of an
Overload flag the node monitors the bus until it detects a transition from a dominant to a recessive
bit. At this point of time every bus node has finished sending its Overload flag and all nodes start
transmission of seven more recessive bits in coincidence.
3.2.5
Interframe space
Data frames and Remote frames are separated from preceding frames, whatever type they may
be (Data frame, Remote frame, Error frame, Overload frame), by a field called Interframe space.
In contrast, Overload frames and Error frames are not preceded by an Interframe space and
multiple Overload frames are not separated by an Interframe space.
The Interframe space contains the bit fields INTERMISSION and Bus idle and, for error- passive
nodes, which have been the transmitter of the previous message, Suspend transmission
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
3-9
38
Freescale Semiconductor, Inc.
(1) For nodes which are not error-passive or have been a receiver of the previous message, see
Figure 3-9 and Figure 3-11(page 1 of 2).
Freescale Semiconductor, Inc...
3
Interframe space
Frame
Intermission
Frame
Bus idle
Figure 3-9 Interframe space (1)
(2) For error-passive nodes which have been the transmitter of the previous message, see
Figure 3-10 and Figure 3-11 (page 2 of 2).
Interframe space
Frame
Suspend
transmission
Intermission
Figure 3-10
3.2.5.1
Frame
Bus idle
Interframe space (2)
INTERMISSION
INTERMISSION consists of three recessive bits.
During INTERMISSION no node is allowed to start transmission of a Data frame or Remote frame.
The only action permitted is signalling of an Overload condition.
3.2.5.2
Bus idle
The period of Bus idle may be of arbitrary length. The bus is recognized to be free, and any node
having something to transmit can access the bus. A message, pending during the transmission of
another message, is started in the first bit following INTERMISSION.
The detection of a dominant bit on the bus is interpreted as Start of frame.
MOTOROLA
3-10
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
39
16
CRC Þeld
8
8
15
CRC
IdentiÞer
Acceptance
Þltering
Reserved bits
d d d
CRC Del
Acknowledge
Ack Del
4
DLC0
11
8N (0 ≤ N ≤ 8)
Data Þeld
6
Control Þeld
ID0
RTR
RB1
RB0
DLC3
Start of frame
ID10
12
Arbitration Þeld
d
r
7
End of frame
r r r r r r r r
Data
length
code
Stored in buffers
Stored in transmit/receive buffers
Bit stufÞng
d
r d d
4
DLC0
11
6
Control Þeld
ID0
RTR
RB1
RB0
DLC3
12
Arbitration Þeld
16
CRC Þeld
15
CRC
CRC Del
Acknowledge
Ack Del
(number of bits = 44)
Remote frame
Start of frame
ID10
Figure 3-11 CAN frame formats (Page 1 of 2)
MESSAGE TRANSFER
Freescale Semiconductor, Inc...
CAN PROTOCOL
Rev. 3
(number of bits = 44 + 8N)
Data frame
r
7
End of frame
Note:
A remote frame is identical to a data
frame, except that the RTR bit is
recessive, and there is no data Þeld.
r r r r r r r r
MOTOROLA
3-11
3
40
Data frame
or
remote frame
≤6
Echo
error ßag
6
Error ßag
d d d d d d d
8
Inter-frame space
or
overload frame
Error delimiter
Inter-frame space
3
Any frame
8
Suspend
transmit
INT
Note:
An error frame can start anywhere in the
middle of a frame.
Note:
INT = Intermission
Suspend transmission is only for error
passive nodes.
Note:
An overload frame can only start at the end
of a frame.
Maximum echo of overload ßag is one bit.
d d r r r r r r r r
Bus idle
r r r r r r r r r r r r r r r r r r r r
Start of frame
Figure 3-11 CAN frame formats (Page 2 of 2)
MESSAGE TRANSFER
CAN PROTOCOL
Rev. 3
Freescale Semiconductor, Inc...
3
MOTOROLA
3-12
Error frame
Data frame
or
remote frame
r r r d
Overload frame
End of frame
or
error delimiter
or
overload delimiter
6
8
Overload ßag
Overload delimiter
d d d d d d d r r r r r r r r
Inter-frame space
or
error frame
41
Freescale Semiconductor, Inc.
3.2.5.3
Suspend transmission
Freescale Semiconductor, Inc...
After an error-passive node has transmitted a frame, it sends eight recessive bits following
INTERMISSION, before starting to transmit a further message or recognizing the bus to be idle.
If, meanwhile, a transmission (caused by another node) starts, the node will become the receiver
of this message.
3.3
3
Message validation
The point in time at which a message is taken to be valid is different for the transmitter and the
receivers of the message.
3.3.1
Transmitter
The message is valid for the transmitter if there is no error until the End of frame. If a message is
corrupted, retransmission will follow automatically and according to the rules of prioritization. In
order to be able to compete for bus access with other messages, retransmission has to start as
soon as the bus is idle.
3.3.2
Receiver
The message is valid for the receiver if there is no error until the last but one bit of End of frame.
3.4
Bit-stream coding
The frame segments Start of frame, Arbitration field, Control field, Data field and CRC Sequence
are coded by the method of bit stuffing. Whenever a transmitter detects five consecutive bits of
identical value in the bit-stream to be transmitted, it automatically inserts a complementary bit in
the actual transmitted bit-stream.
The remaining bit fields of the Data frame or Remote frame(CRC Delimiter, ACK field and End of
frame) are of fixed form and not stuffed.
The Error frame and the Overload frame are also of fixed form and are not coded by the method
of bit stuffing.
The bit-stream in a message is coded according to the Non-Return-to-Zero (NRZ) method. This
means that during the total bit time the generated bit level is either dominant or recessive.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
3-13
42
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
3
THIS PAGE LEFT BLANK INTENTIONALLY
MOTOROLA
3-14
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
43
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
4
4
ERROR HANDLING
4.1
Error detection
There are five different error types (which are not mutually exclusive). The following sections
describe these errors.
4.1.1
Bit error
A node which is sending a bit on the bus also monitors the bus. The node must detect, and interpret
as a Bit error, the situation where the bit value monitored is different from the bit value being sent.
An exception to this is the sending of a recessive bit during the stuffed bit-stream of the Arbitration
field or during the ACK Slot; in this case no Bit error occurs when a dominant bit is monitored.
A transmitter sending a PASSIVE Error flag and detecting a dominant bit does not interpret this as
a Bit error.
4.1.2
Stuff error
A Stuff error must be detected and interpreted as such at the bit time of the sixth consecutive equal
bit level (6 consecutive dominant or 6 consecutive recessive levels), in a message field which
should be coded by the method of bit stuffing.
4.1.3
CRC error
The CRC sequence consists of the result of the CRC calculation by the transmitter.
The receivers calculate the CRC in the same way as the transmitter. A CRC error must be
recognized if the calculated result is not the same as that received in the CRC sequence.
TPG
CAN PROTOCOL
Rev. 3
ERROR HANDLING
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
4-1
44
Freescale Semiconductor, Inc.
4.1.4
Form error
A FORM error must be detected when a fixed-form bit field contains one or more illegal bits.
Freescale Semiconductor, Inc...
4
4.1.5
Acknowledgement error
An Acknowledgement error must be detected by a transmitter whenever it does not monitor a
dominant bit during ACK Slot
4.2
Error signalling
A node detecting an error condition signals this by transmitting an Error flag. An error-active node
will transmit an ACTIVE Error flag; an error-passive node will transmit a PASSIVE Error flag.
Whenever a Bit error, a Stuff error, a Form error or an Acknowledgement error is detected by any
node, that node will start transmission of an Error flag at the next bit time.
Whenever a CRC error is detected, transmission of an Error flag will start at the bit following the
ACK Delimiter, unless an Error flag for another error condition has already been started.
TPG
MOTOROLA
4-2
ERROR HANDLING
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
45
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
5
FAULT CONFINEMENT
5.1
5
CAN node status
With respect to fault confinement, a node may be in one of three states: error-active, error-passive,
or bus-off.
An error active node can normally take part in bus communication and sends an ACTIVE Error flag
when an error has been detected.
An error-passive node must not send an ACTIVE Error flag. It takes part in bus communication,
but when an error has been detected only a PASSIVE Error flag is sent. Also after a transmission,
an error-passive node will wait before initiating a further transmission. (See Section 3.2.5.3)
A bus-off node is not allowed to have any influence on the bus (e.g. output drivers switched off).
5.2
Error counts
To facilitate fault confinement two counts are implemented in every bus node:
•
TRANSMIT ERROR COUNT
•
RECEIVE ERROR COUNT
These counts are modified according to the following 12 rules:
Note:
More than one rule may apply during a given message transfer
1) When a RECEIVER detects an error, the RECEIVE ERROR COUNT will be
increased by 1, except when the detected error was a Bit error during the
sending of an ACTIVE Error flag or an Overload.
2) When a RECEIVER detects a dominant bit as the first bit after sending an
Error flag, the RECEIVE ERROR COUNT will be increased by 8.
CAN PROTOCOL
Rev. 3
FAULT CONFINEMENT
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
5-1
46
Freescale Semiconductor, Inc.
3) When a TRANSMITTER sends an Error flag, the TRANSMIT ERROR
COUNT is increased by 8.
Exception 1
The TRANSMIT ERROR COUNT is not changed if:
–
Freescale Semiconductor, Inc...
5
The TRANSMITTER is error-passive
and
–
the TRANSMITTER detects an Acknowledgement error because of not
detecting a dominant ACK
and
–
the TRANSMITTER does not detect a dominant bit while sending its
PASSIVE Error flag
Exception 2
The TRANSMIT ERROR COUNT is not changed if:
–
The TRANSMITTER sends an Error flag because a Stuff error occurred
during Arbitration (whereby the Stuff bit is located before the RTR bit)
and
–
the Stuff bit should have been recessive
and
–
the Stuff bit has been sent as recessive but is monitored as dominant
4) An error-active TRANSMITTER detects a Bit error while sending an ACTIVE
Error flag or an Overload flag, the TRANSMIT ERROR COUNT is increased
by 8.
5) An error-active RECEIVER detects a bit error while sending an ACTIVE
Error flag or an Overload flag, the RECEIVE ERROR COUNT is increased
by 8.
6) Any node tolerates up to 7 consecutive dominant bits after sending an
ACTIVE Error flag or a PASSIVE Error flag. After detecting the eighth
consecutive dominant bit s and after each sequence of additional eight
consecutive dominant bits, every TRANSMITTER increases its TRANSMIT
ERROR COUNT by 8 and every RECEIVER increases its RECEIVE
ERROR COUNT by 8.
7) After the successful transmission of a message (getting ACK and no error
until End of frame is finished), the TRANSMIT ERROR COUNT is decreased
by 1, unless it was already 0.
MOTOROLA
5-2
FAULT CONFINEMENT
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
47
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
8) After the successful reception of a message (reception without error up to
the ACK Slot and the successful sending of the ACK bit), the RECEIVE
ERROR COUNT is decreased by 1, if it was between 1 and 127. If the
RECEIVE ERROR COUNT was 0, it stays 0, and if it was greater than 127,
then it will be set to a value between 119 and 127.
9) A node is error passive when the TRANSMIT ERROR COUNT equals or
exceeds 128, or when the RECEIVE ERROR COUNT equals or exceeds
128. An error condition letting a node become error-passive causes the node
to send an ACTIVE Error flag.
10) A node is bus-off when the TRANSMIT ERROR COUNT is greater than or
equal to 256.
5
11) An error-passive node becomes error-active again when both the
TRANSMIT ERROR COUNT and the RECEIVE ERROR COUNT are less
than or equal to 127.
12) A node which is bus-off is permitted to become error-active (no longer
bus-off) with its error counters both set to 0 after 128 occurrences of 11
consecutive recessive bits have been monitored on the bus.
Note:
An error count value greater than about 96 indicates a heavily disturbed bus. It may be
advantageous to provide the means to test for this condition.
Note:
Start-up/Wake-up
If during system start-up only one node is on line, and if this node transmits some
message, it will get no acknowledgement, detect an error and repeat the message. It
can become “error-passive” but not bus-off due to this reason.
CAN PROTOCOL
Rev. 3
FAULT CONFINEMENT
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
5-3
48
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
5
THIS PAGE LEFT BLANK INTENTIONALLY
MOTOROLA
5-4
FAULT CONFINEMENT
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
49
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
6
BIT TIMING REQUIREMENTS
6.1
6
Nominal bit rate
The Nominal bit rate is the number of bits per second transmitted in the absence of
resynchronization by an ideal transmitter.
6.2
Nominal bit time
NOMINAL BIT TIME = 1 / NOMINAL BIT RATE
The Nominal bit rate can be thought of as being divided into separate non-overlapping time
segments. These segments are as shown below, and form the bit time as shown in Figure 6-1.
•
SYNCHRONIZATION SEGMENT (SYNC_SEG)
•
PROPAGATION TIME SEGMENT (PROP_SEG)
•
PHASE BUFFER SEGMENT1 (PHASE_SEG1)
•
PHASE BUFFER SEGMENT2 (PHASE_SEG2)
NOMINAL BIT TIME
SYNC_SEG
PROP_SEG
PHASE_SEG1
PHASE_SEG2
Sample Point
Figure 6-1 Nominal bit time
CAN PROTOCOL
Rev. 3
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
6-1
50
Freescale Semiconductor, Inc.
6.3
SYNC_SEG
This part of the bit time is used to synchronize the various nodes on the bus. An edge is expected
to lie within this segment
Freescale Semiconductor, Inc...
6.4
6
PROP_SEG
This part of the bit time is used to compensate for the physical delay times within the network. It is
twice the sum of the signal’s propagation time on the bus line, the input comparator delay, and the
output driver delay.
6.5
PHASE_SEG1, PHASE_SEG2
These Phase-Buffer-Segments are used to compensate for edge phase errors. These segments
can be lengthened or shortened by resynchronization.
6.6
Sample point
The Sample point is the point in time at which the bus level is read and interpreted as the value of
that respective bit. Its location is at the end of PHASE_SEG1.
6.7
Information processing time
The Information processing time is the time segment starting with the Sample point reserved for
calculation of the subsequent bit level.
6.8
Time quantum
The Time quantum is a the fixed unit of time which can be derived from the oscillator period. There
is a programmable prescaler, with integral values (with a range of at least 1 to 32) which allows a
fixed unit of time, the Time quantum can have a length of
TIME QUANTUM = m × MINIMUM TIME QUANTUM
where m is the value of the prescaler.
MOTOROLA
6-2
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
51
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
6.8.1
Length of time segments
•
SYNC_SEG is 1 Time quantum long.
•
PROP_SEG is programmable to be 1, 2, ......8 Time quanta long.
•
PHASE_SEG1 is programmable to be 1, 2, ......8 Time quanta long.
•
PHASE_SEG2 is the maximum of PHASE_SEG1 and the Information processing time.
•
The Information processing time is less than or equal to 2 Time quanta long.
The total number of Time quanta in a bit time must be programmable over a range of at least 8 to
25.
6.9
Synchronization
6.9.1
Hard synchronization
6
After a Hard synchronization the internal bit time is restarted with SYNC_SEG. Thus Hard
synchronization forces the edge which has caused the Hard synchronization to lie within the
Synchronization segment of the restarted bit time.
6.9.2
Resynchronization jump width
As a result of resynchronization, PHASE_SEG1 may be lengthened or PHASE_SEG2 may be
shortened. The amount by which the Phase buffer segments may be altered may not be greater
than the Resynchronization jump width. The Resynchronization jump width is programmable
between 1 and the smaller of 4 and PHASE_SEG1 Time quanta.
Clocking information may be derived from transitions from one bit value to the other. The property
that only a fixed maximum number of successive bits have the same value provides the possibility
of resynchronising a bus node to the bit-stream during a frame.
The maximum length between two transitions which can be used for resynchronization is 29 bit
times.
CAN PROTOCOL
Rev. 3
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
6-3
52
Freescale Semiconductor, Inc.
6.9.3
Phase error of an edge
Freescale Semiconductor, Inc...
The PHASE error of an edge is given by the position of the edge relative to SYNC_SEG, measured
in Time quanta. The sign of PHASE error is defined as follows:
6
e
< 0
if the edge lies after the Sample point of the previous bit,
e
= 0
if the edge lies within SYNC_SEG,
e
> 0
if the edge lies before the Sample point.
6.9.4
Resynchronization
The effect of a Resynchronizationis the same as that of Hard synchronization, when the magnitude
of the PHASE error of the edge which causes the Resynchronization is less than or equal to the
programmed value of the Resynchronization jump width.
When the magnitude of the PHASE error is larger than the Resynchronizationjump width, and if
the PHASE error is positive, then PHASE_SEG1 is lengthened by an amount equal to the
Resynchronization jump width.
When the magnitude of the PHASE error is larger than the Resynchronization jump width, and if
the PHASE error is negative, then PHASE_SEG2 is shortened by an amount equal to the
Resynchronization jump width.
6.9.5
Synchronization rules
Hard synchronization and Resynchronization are the two forms of synchronization. They obey the
following rules:
1) Only one synchronization within one bit time is allowed.
2) An edge will be used for synchronization only if the value detected at the
previous Sample point (previous read bus value) differs from the bus value
immediately after the edge.
3) Hard synchronization is performed whenever there is a recessive to
dominant edge during Bus idle.
4) All other recessive to dominant edges (and optionally dominant to recessive
edges in the case of low bit rates) fulfilling the rules 1 and 2 will be used for
Resynchronization with the exception that a transmitter will not perform a
Resynchronization as a result of a recessive to dominant edge with a
positive PHASE error, if only recessive to dominant edges are used for
Resynchronization.
MOTOROLA
6-4
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
53
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
7
INCREASING OSCILLATOR TOLERANCE
This section describes an upwards compatible modification to the CAN protocol, as specified in
Sections 1 to 6.
7
7.1
Protocol modifications
In order to increase the maximum oscillator tolerance above the 0.5% currently possible, the
following modifications, which are upwards compatible with the existing CAN specification, are
necessary:
1) If a CAN node samples a dominant bit at the third bit of INTERMISSION,
then it will interpret this bit as a Start of frame bit.
2) If a CAN node has a message waiting for transmission and it samples a
dominant bit at the third bit of INTERMISSION, it will interpret this as a Start
of frame bit, and, with the next bit, start transmitting its message with the first
bit of its Identifier without first transmitting a Start of frame bit and without
becoming a receiver.
3) If a CAN node samples a dominant bit at the eighth bit (the last bit) of an
ERROR Delimiter or Overload Delimiter, it will, at the next bit, start
transmitting an Overload frame (not an Error frame). The Error Counters will
not be incremented.
4) Only recessive to dominant edges will be used for synchronization.
In agreement with the existing specification, the following rules are still valid:
5) All CAN controllers synchronize on the Start of frame bit with a hard
synchronization.
6) No CAN controller will send a Start of frame bit until it has counted three
recessive bits of INTERMISSION.
These modifications allow a maximum oscillator tolerance of 1.58% and the use of a ceramic
resonator at bus speeds up to 125 kbits/second. For the full bus speed range of the CAN protocol,
a quartz oscillator is still required. The compatibility of the enhanced and the existing protocol is
maintained, as long as:
CAN PROTOCOL
Rev. 3
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
7-1
54
Freescale Semiconductor, Inc.
7) CAN controllers with the enhanced and existing protocols, used in one and
the same network, are all provided with a quartz oscillator.
Freescale Semiconductor, Inc...
The chip with the highest requirement for its oscillator accuracy determines the oscillator accuracy
which is required from all the other nodes. Ceramic resonators can only be used when all the
nodes in the network use the enhanced protocol.
7.2
Determination of the maximum synchronization length
As a basis for the calculation of the maximum oscillator tolerance, the maximum distance between
two edges used for resynchronization and the minimum synchronization length necessary to
correctly extract the information coded into the bit-stream will be determined.
7
7.2.1
Local error, where at least two of the nodes are Error
ACTIVE
The distance from the last recessive to dominant edge to the next possible Start of frame is 29 bits.
According to the rules of fault confinement, a receiver will increment its RECEIVE ERROR COUNT
depending on the first bit after sending an Error flag. Therefore, receivers have to be able to
distinguish between sequences of 12 and of 13 dominant bits.
Receiver(s): Stuff Error because of Local Bit Error
INTERMISSION
Stuff
Error
Stuffed Data
Error flag
Wait for Delimiter
Error Delimiter
x
1 2
3 4
5 1
1 2
3 4
5 6
1 2
3 4
5
6
1 2
3 4
5 6
7 8
1 2
3 x
x
1 2
3 4
5 6
7 8
9 10 11 1
1 2
3 4
5
6
1 2
3 4
5 6
7 8
1 2
3 x
Stuffed Data
Error flag
Error Delimiter
Stuff
Error
Transmitter: Stuff Error because of monitored Error flag
INTERMISSION
Figure 7-1 Local error
MOTOROLA
7-2
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
55
Freescale Semiconductor, Inc.
7.2.2
Two consecutive Overload frames
Transmitter and Receiver(s)
possible next
Overload flag
Freescale Semiconductor, Inc...
2
3 4
5 6
End of frame
7 1
1 2
3 4
Overload flag
5 6
1 2
3 4
5 6
7 8 1 2
3 x
Overload Delimiter
foreign
Overload
flag
INTERMISSION
7
Figure 7-2 Two consecutive Overload frames
The distance from the start of the first Overload flag to the next recessive to dominant edge at the
start of the second Overflow is 15 bits.
CAN PROTOCOL
Rev. 3
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
7-3
56
Freescale Semiconductor, Inc.
7.2.3
Acknowledge error at transmitter, where all nodes are
Error PASSIVE
Freescale Semiconductor, Inc...
The distance from the last recessive to dominant edge to the next possible Start of frame is 29 bits.
Since there is only one transmitter, the exact length of SUSPEND TRANSMISSION is not
significant in this case, as long as it is at least 3 bits.
7
Receiver(s): CRC Error because of preceding Local Bit Error
CRC
Delimiter
CRC
ACK Field
Error flag
INTERMISSION
Error Delimiter
x 1 2 3 4 5 6 7 8 9 1 1 2 1 2 3 4 5 6 1 2 3 4 5 6 7 8 1 2 3 x
x 1 2 3 4 5 6 7 8 9 1 1 1 2 3 4 5 6 1 2 3 4 5 6 7 8 1 2 3 1 2 3 4 5 6 7 8 x
CRC
CRC
Delimiter
Error flag
ACK Slot
Error Delimiter
SUSPEND
INTERMISSION
Transmitter: Acknowledgement Error
Figure 7-3 Acknowledge error at transmitter, all nodes Error PASSIVE
MOTOROLA
7-4
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
57
Freescale Semiconductor, Inc.
7.2.4
Local error at transmitter, where all nodes are Error
PASSIVE
Freescale Semiconductor, Inc...
The distance from the last recessive to dominant edge to the next possible Start of frame is 28 bits
for receivers and 30 bits for transmitters (during Arbitration, there can be more than one transmitter
and therefore, SUSPEND TRANSMISSION has to be taken into consideration).
Receiver(s): Stuff Error
Bit
Error
Arbitration
INTERMISSION
Error flag
Error Delimiter
x
1 2
3 4
5 6
7 8
9 10 1 1
2 3 4 5
6 1
2 3
4 5
6 7
8 1
2 3
x
1 2
3 4
1 1
2 3
4 5
2 3 4 5
6 7
8 1
2 3
1 2
3 4
5 6 7 8
Error flag
Arbitration
6 1
Error Delimiter
x
7
x
SUSPEND
INTERMISSION
Bit
Error
Transmitter: Local Bit Error
Figure 7-4 Local error at transmitter, all nodes Error PASSIVE
CAN PROTOCOL
Rev. 3
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
7-5
58
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
7
7.3
Bit timing
7.3.1
Construction of the bit timing for maximum oscillator
tolerance
The maximum oscillator tolerance is reached when the length of the PHASE BUFFER SEGMENTs
is the same as the maximum Resynchronization jump width and when only one Time quantum is
used for delay compensation.
The delay to be compensated for due to the bit-wise arbitration mechanism is two times the sum of:
•
the delay of the driver circuit
•
the delay of the bus line
•
the delay of the receiver circuit
Assumptions (dependent on the external circuitry):
delay of driver
=
200 ns
delay of bus line (40 m)
=
220 ns
delay of receiver circuit
=
80 ns
This allows a Time quantum of 1 µs and a maximum bit rate of 100 kbits/second with the maximum
possible oscillator tolerance.
NOMINAL BIT TIME
SYNC PROP
SEG SEG
PHASE_SEG1
PHASE_SEG2
TIME QUANTUM
Figure 7-5 Bit timing for maximum oscillator tolerance
MOTOROLA
7-6
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
59
Freescale Semiconductor, Inc.
7.3.2
Construction of the bit timing for maximum bit rate
The largest possible part of the bit time will be used for delay compensation. PHASE_SEG1 and
Resynchronization jump width will be limited to 1 Time quantum.
Assumptions (dependent on the external circuitry):
delay of driver = 50 ns
Freescale Semiconductor, Inc...
delay of bus line (40 m) = 220 ns
delay of receiver circuit = 30 ns
With a Time quantum of 100 ns, 6 Time quanta are needed for delay compensation. This allows a
bit rate of 1 Mbits/second.
7
NOMINAL BIT TIME
SYNC
SEG
PROP_SEG
PHASE
PHASE_SEG2
SEG1
TIME QUANTUM
Figure 7-6 Bit timing for maximum bit rate
CAN PROTOCOL
Rev. 3
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
7-7
60
Freescale Semiconductor, Inc.
7.4
Calculation of the oscillator tolerance
In the following discussion, BT is the NOMINAL BIT TIME, SJW the RESYNCHRONIZATION
JUMP WIDTH, PS1 and PS2 the length of the PHASE SEGMENTs, and df the modulus of the
difference between the actual and nominal oscillator frequency relative to the nominal oscillator
frequency.
Freescale Semiconductor, Inc...
The CAN protocol requires that:
7
SJW ≤ min(PS1, PS2)
[1]
BT > PS1 + PS2
[2]
BT > 2 SJW
[3]
PS2 ≥ PS1
[4]
In order to be able to sample correctly the first bit after sending an ACTIVE Error flag (essential for
the correct localization of bus errors, see 7.2.1), the oscillator tolerance is limited to:
(2 x df) x (13 x BT - PS2) < min(PS1, PS2)
[5]
The worst case of 13 bits occurs after a STUFF Error on what should have been a recessive stuff
bit. In this case the 13th bit after the last recessive to dominant edge needs to be correctly sampled
for fault confinement.
For correct synchronization in the stuffed part of the bit-stream:
(2 x df) x 10 x BT < SJW
[6]
For correct resynchronization until the next Start of frame (worst case, see Figure 6.9):
(2 x df) x (30 x BT - PS2) < min(PS1, PS2)
[7]
Similarly, if resynchronization occurs on both edges:
(2 x df) x (26 x BT - PS2) < min(PS1, PS2)
[8]
If [7] and [8] are fulfilled, [5] and [6] are fulfilled likewise.
In the following, the maximum oscillator tolerances of the actual and the enhanced CAN protocol
are examined.
MOTOROLA
7-8
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
61
Freescale Semiconductor, Inc.
7.5
Maximum oscillator tolerances
From 7.4 it follows that with PS1, PS2 = 0.4 x BT and SJW = 0.4 x BT the oscillator tolerance is at
its maximum.
Freescale Semiconductor, Inc...
7.5.1
Oscillator tolerance for existing CAN protocol
Synchronization only on edges from recessive to dominant:
[7] ⇒
(2 x df) x (30 x BT - 0.4 x BT) < 0.4 x BT
df < 0.675 %
7
Synchronization only both edges:
[8] ⇒
(2 x df) x (26 x BT - 0.4 x BT) < 0.4 x BT
df < 0.781 %
7.5.2
Oscillator tolerance for enhanced CAN protocol
The effect of the modifications described here is to reduce the number of consecutive bit times
over which synchronization must be maintained. This is done by allowing the node to tolerate, after
certain particularly long sequences of equal bits, phase shifts of up to a whole bit time.
Between the last recessive to dominant edge of a frame and the start of the next frame, there can
be up to 30 bits. Modification 1 allows a tolerance of one logical bit here and ensures that if [9]
holds (implied by [5]), that bus arbitration according to message Identifier priority will take place.
[3], [5], [6] ⇒
(2 x df) x (33 x BT - PS2) < BT + min(PS1, PS2)
[9]
Therefore, if [5] is satisfied, we can tolerate sequences of up to at least 33 bits from a
synchronization if an error of one logical bit can be tolerated in the synchronized sampled
bit-stream.
Example 7.2.2 regards the case if the first bit of INTERMISSION is the 16th bit after the last
recessive to dominant edge at the start of the first Overload frame. This implies that we have to
allow a tolerance of one logical bit here for the start of the second Overload frame. Modification 3
caters for this.
All other sequences are covered by the preceding cases or by a thirteen bit synchronization length.
With the first three modifications to the CAN protocol, resychronization on recessive to dominant
edges as well as dominant to recessive edges has absolutely no advantage over
CAN PROTOCOL
Rev. 3
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
7-9
62
Freescale Semiconductor, Inc.
resynchronization only on recessive to dominant edges. Hence modification 4 is introduced to
avoid unnecessary complications to CAN implementations.
With the enhanced protocol the oscillator tolerance is given by
df < min(PS1, PS2) / (2 x (13 x BT - PS2))
and
Freescale Semiconductor, Inc...
df < SJW / (2 x (10 x BT))
7
With PS1, PS2 = 0.4 x BT and SJW = 0.4 x BT an oscillator tolerance of
df < 1.58 %
can be allowed.
7.6
Resynchronization
In the existing CAN specification, the CAN controller was programmable to allow the use of only
recessive to dominant edges for resynchronization, or of both recessive to dominant and dominant
to recessive. With these protocol modifications, the oscillator tolerance is the same for both ways
of resynchronization and therefore, the use of both edges brings no advantage and this feature
can be removed.
7.7
Compatibility of existing and enhanced CAN protocols
Controllers using the existing CAN protocol must be equipped with a quartz oscillator. Controllers
which use the enhanced protocol may be equipped with a quartz oscillator or a ceramic resonator.
The following example shows that it is not possible to employ controllers using the existing CAN
protocol together with controllers using the enhanced CAN protocol and driven by a ceramic
resonator.
If no Error frame occurs, the longest bit sequence without the possibility of resynchronization
occurs at the end of the message. In this case the synchronization length is 13 bits, resulting in a
maximum phase shift between a quartz and ceramic node of (see Section 6.8), which can be
tolerated by both existing and enhanced protocols.
Otherwise, if an Error frame or an Overload frame occurs, the next Start of frame bit, of a
transmitter driven by a ceramic oscillator of minimum frequency, will be interpreted by a receiver
driven by a quartz oscillator of maximum frequency and using the original CAN protocol as an
Overload flag and will cause the transmission of another Overload frame. This will be repeated
until the RECEIVE ERROR COUNT of the transmitter of the Start of frame bit (counting stuff errors
after losing arbitration) reaches the error passive limit.
MOTOROLA
7-10
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
63
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
This review comes to the conclusion, that CAN controllers with the enhanced and existing
protocols can be used in one and the same network, provided that all nodes are driven with a
quartz oscillator. The chip with the highest requirement for its oscillator accuracy determines the
oscillator accuracy which is required from all the other nodes. Ceramic resonators can only be
used when all the nodes in the network use the enhanced protocol.
7.8
Assessment
Standard devices are subject to production variations, temperature dependency, and ageing which
are specified as a tolerance. Most standard devices meet the following tolerances:
quartz crystal df ≤ 0.1 %
ceramic resonator df ≤ 1.2 %
Together with the results from sections 7.3 and 7.5, this means that, with the enhanced protocol,
ceramic resonators can be used for bit rates up to and including 125 kbits/second. For higher bit
rates a quartz oscillator is still required.
CAN PROTOCOL
Rev. 3
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
7
MOTOROLA
7-11
64
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
7
THIS PAGE LEFT BLANK INTENTIONALLY
MOTOROLA
7-12
INCREASING OSCILLATOR TOLERANCE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
65
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
BOSCH
CONTROLLER AREA NETWORK (CAN)
VERSION 2.0
PART B
TPG
CAN PROTOCOL
Rev. 3
BOSCH CONTROLLER AREA NETWORK (CAN)
For More Information
This
VERSION 2.0 On
PART
B Product,
Go to: www.freescale.com
MOTOROLA
66
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
THIS PAGE LEFT BLANK INTENTIONALLY
TPG
MOTOROLA
BOSCH CONTROLLER AREA NETWORK (CAN)
CAN PROTOCOL
For MoreVERSION
Information
OnB This Product,
2.0 PART
Rev. 3
Go to: www.freescale.com
67
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
8
INTRODUCTION
The Controller Area Network (CAN) is a serial communications protocol that efficiently supports
distributed real-time control with a very high level of data integrity.
Though conceived and defined by BOSCH in Germany for automotive applications, CAN is not
restricted to that industry. CAN fulfils the communication needs of a wide range of applications,
from high-speed networks to low-cost multiplex wiring.
For example, in automotive electronics, engine control units, sensors and anti-skid systems may
be connected using CAN, with bit-rates up to 1 Mbit/s. At the same time, it is cost effective to build
CAN into vehicle body electronics, such as lamp clusters and electric windows, to replace the
wiring harness otherwise required.
8
The intention of the CAN specification is to achieve compatibility between any two CAN
implementations. Compatibility, however, has different aspects with respect to, for example,
electrical features and the interpretation of data to be transferred.
To achieve design transparency and implementation flexibility CAN has been subdivided into
different layers according to the ISO/OSI Reference Model:
•
•
The Data Link Layer
–
the Logical Link Control (LLC) sublayer
–
the Medium Access Control (MAC) sublayer
The Physical Layer
In previous versions of the CAN specification the services and functions of the LLC and MAC
sublayers of the Data Link Layer were described as layers called Object Layer and Transfer Layer.
The scope of the LLC sublayer includes: determining which messages received by the LLC
sublayer are actually to be accepted; providing services for data transfer and for remote data
request; and providing the means for recovery management and overload notifications. There is
considerable freedom in defining object handling.
The MAC sublayer is principally concerned with the transfer protocol, i.e. controlling the framing,
performing arbitration, error checking, error signalling and fault confinement. Within the MAC
sublayer it is decided whether the bus is free for starting a new transmission, or whether reception
of a message is just starting. Also, some general features of the bit-timing are regarded as part of
the MAC sublayer. Modifications to the MAC sublayer cannot be made.
TPG
CAN PROTOCOL
Rev. 3
INTRODUCTION
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
8-1
68
Freescale Semiconductor, Inc.
The Physical Layer covers the actual transfer of the bits between the different nodes, with respect
to all electrical properties. Within a network the physical layer has to be the same for all nodes.
However, there are many possible implementations of the Physical Layer.
Freescale Semiconductor, Inc...
The remainder of this document is principally concerned with the definition of the MAC sublayer
and a small part of the LLC sublayer of the Data Link Layer, and the consequences of the CAN
protocol for the surrounding layers.
8
TPG
MOTOROLA
8-2
INTRODUCTION
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
69
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
9
BASIC CONCEPTS
9.1
Layered structure of a CAN node
The LLC sublayer is concerned with message filtering, overload notification and recovery
management.
The MAC sublayer represents the kernel of the CAN protocol. It presents messages received to
the LLC sublayer and accepts messages to be transmitted by the LLC sublayer. The MAC sublayer
is responsible for message framing, arbitration, acknowledgement, error detection and signalling.
The MAC sublayer is supervised by a self checking mechanism, called fault confinement, which
distinguishes short disturbances from permanent failures.
9
The Physical Layer defines how signals are actually transmitted, dealing with the descriptions of
bit timing, bit encoding and synchronization. The Physical Layer is not defined here, as it will vary
according to the requirements of individual applications (for example, transmission medium and
signal level implementations).
9.2
Messages
Information on the bus is sent in fixed format messages of different but limited length (see
Section 10). When the bus is free, any connected node may start to transmit a new message.
9.2.1
Information routing
In CAN systems a node does not make use of any information about the system configuration (e.g.
node addresses). This has several important consequences, which are described below.
CAN PROTOCOL
Rev. 3
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
9-1
70
Freescale Semiconductor, Inc.
APPLICATION LAYER
Freescale Semiconductor, Inc...
CAN LAYERS
DATA LINK
LLC sublayer
MAC sublayer
PHYSICAL
9
SUPERVISOR
Acceptance Filtering
Overload NotiÞcation
Recovery Management
Data Encapsulation/Decapsulation
Frame Coding (StufÞng/DestufÞng)
Medium Access Management
Error Detection
Error Signalling
Acknowledgement
Serialization/Deserialization
Fault
ConÞnement
Bit Encoding/Decoding
Bit Timing
Synchronization
Bus Failure
Management
Driver/Receiver Characteristics
CAN Network
Figure 9-1
9.2.1.1
CAN layers
System flexibility
Nodes may be added to the CAN network without requiring any change in the software or
hardware of any node or the application layer.
MOTOROLA
9-2
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
71
Freescale Semiconductor, Inc.
9.2.1.2
Message routing
The content of a message is described by an Identifier. The Identifier does not indicate the
destination of the message, but describes the meaning of the data, so that all nodes in the network
are able to decide by MESSAGE FILTERING whether the data is to be acted upon by them or not.
Freescale Semiconductor, Inc...
9.2.1.3
Multicast
As a consequence of the concept of MESSAGE FILTERING any number of nodes may receive
and act simultaneously upon the same message.
9.2.1.4
Data consistency
Within a CAN network it is guaranteed that a message is accepted simultaneously either by all
nodes or by no node. Thus data consistency is a property of the system achieved by the concepts
of multicast and by error handling.
9.3
9
Bit-rate
The speed of CAN may be different in different systems. However, in a given system the bit-rate is
uniform and fixed.
9.4
Priorities
The Identifier defines a static message priority during bus access.
9.5
Remote data request
By sending a Remote frame a node requiring data may request another node to send the
corresponding Data frame. The Data frame and the corresponding Remote frame have the same
Identifier.
CAN PROTOCOL
Rev. 3
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
9-3
72
Freescale Semiconductor, Inc.
9.6
Multi-master
When the bus is free any node may start to transmit a message. The node with the message of
highest priority to be transmitted gains bus access.
Freescale Semiconductor, Inc...
9.7
9
Arbitration
Whenever the bus is free, any node may start to transmit a message. If two or more nodes start
transmitting messages at the same time, the bus access conflict is resolved by bit-wise arbitration
using the Identifier. The mechanism of arbitration guarantees that neither information nor time is
lost. If a Data frame and a Remote frame with the same Identifier are initiated at the same time,
the Data frame prevails over the Remote frame. During arbitration every transmitter compares the
level of the bit transmitted with the level that is monitored on the bus. If these levels are equal the
node may continue to send. When a recessive level is sent, but a dominant level is monitored (see
Section 9.13), the node has lost arbitration and must withdraw without sending any further bits.
9.8
Data integrity
In order to achieve a very high integrity of data transfer, powerful measures of error detection,
signalling and self-checking are implemented in every CAN node.
9.8.1
Error detection
To detect errors the following measures have been taken:
•
Monitoring (each transmitter compares the bit levels detected on the bus with the bit levels
being transmitted)
•
Cyclic Redundancy Check (CRC)
•
Bit-Stuffing
•
Message Frame Check
MOTOROLA
9-4
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
73
Freescale Semiconductor, Inc.
9.8.2
Performance of error detection
The error detection mechanisms have the following properties:
Freescale Semiconductor, Inc...
•
•
Monitoring:
–
All global errors are detected
–
All local errors at transmitters are detected
CRC:
–
Up to 5 randomly transmitted errors within a sequence are detected
–
Burst errors of length less than 15 in a message are detected
–
Errors of any odd number of bits in a message are detected
The total residual error probability of undetected corrupted messages is less than 4.7 x 10-11.
9.9
Error signalling and recovery time
Corrupted messages are flagged by any node detecting an error. Such messages are aborted and
will be retransmitted automatically. The recovery time from detecting an error until the start of the
next message is at most 31 bit times, provided there is no further error.
9.10
9
Fault confinement
CAN nodes are able to distinguish between short disturbances and permanent failures. Defective
nodes are switched off.
9.11
Connections
The CAN serial communication link is a bus to which a number of nodes may be connected. This
number has no theoretical limit. Practically, the total number of nodes will be limited by delay times
and/or electrical loads on the bus line.
CAN PROTOCOL
Rev. 3
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
9-5
74
Freescale Semiconductor, Inc.
9.12
Single channel
Freescale Semiconductor, Inc...
The bus consists of a single bidirectional channel that carries bits. From this data,
resynchronization information can be derived. The way in which this channel is implemented is not
fixed in this specification, e.g. single wire (plus ground), two differential wires, optical fibres, etc.
9
9.13
Bus values
The bus can have one of two complementary values: dominant or recessive. During simultaneous
transmission of dominant and recessive bits, the resulting bus value will be dominant. For example,
in the case of a wired-AND implementation of the bus, the dominant level would be represented
by a logical ‘0’ and the recessive level by a logical ‘1’.
Physical states (e.g. electrical voltage, light) that represent the logical levels are not given in this
specification.
9.14
Acknowledgement
All receivers check the consistency of the message being received and will acknowledge a
consistent message and flag an inconsistent message.
9.15
Sleep mode/wake-up
To reduce the system’s power consumption, a CAN device may be set into sleep mode, in which
there is no internal activity and the bus drivers are disconnected. The sleep mode is finished with
a wake-up by any bus activity or by internal conditions of the system. On wake-up, the internal
activity is restarted, although the MAC sublayer will wait for the system’s oscillator to stabilize and
then wait until it has synchronized itself to the bus activity (by checking for eleven consecutive
recessive bits), before the bus drivers are set to the on-bus state again.
MOTOROLA
9-6
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
75
Freescale Semiconductor, Inc.
9.16
Oscillator Tolerance
Freescale Semiconductor, Inc...
A maximum oscillator tolerance of 1.58% is given allowing ceramic resonators to be used in
applications with transmission rates of up to 125 kbit/s, as a general rule. For a more precise
evaluation, refer to the following Technical Paper.
“Impact of Bit Representation on Transport Capacity and Clock Accuracy in Serial Data Streams”
by S. Dais and M. Chapman.
SAE Technical Paper Series 890532, Multiplexing in Automobil SP-773, March 1989.
A quartz oscillator is required to achieve the full bus speed range of the CAN protocol.
The chip of the CAN network with the highest requirement for oscillator accuracy determines the
oscillator accuracy from all the other nodes.
Note:
CAN controllers following this CAN Specification and controllers following previous
CAN Specifications 1.0 and 1.1, when used together in one network, must all be
equipped with a quartz oscillator. Ceramic resonators can only be used in a network
where all the nodes of the network follow CAN Specification 1.2 or later.
9
CAN PROTOCOL
Rev. 3
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
9-7
76
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
9
THIS PAGE LEFT BLANK INTENTIONALLY
MOTOROLA
9-8
BASIC CONCEPTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
77
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
10
MESSAGE TRANSFER
10.1
Definition of transmitter/receiver
10.1.1
Transmitter
A node originating a message is called TRANSMITTER of that message. The node continues to
be TRANSMITTER until the bus is idle or the node loses Arbitration.
10.1.2
Receiver
A node is called RECEIVER of a message if it is not the TRANSMITTER of that message, and the
bus is not idle.
10.2
Frame formats
There are two different frame formats which differ from each other by the length of their Identifier
fields. Frames with 11 bit Identifier fields are denoted Standard Frames, while frames with 12 bit
Identifier fields are denoted Extended frames.
10.3
Frame types
Message transfer is manifested and controlled by four different frame types:
•
A Data frame carries data from a transmitter to the receivers.
•
A Remote frame is transmitted by a bus node to request the transmission of the Data frame
with the same Identifier.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
10-1
78
Freescale Semiconductor, Inc.
•
An Error frame is transmitted by any node on detecting a bus error.
•
An Overload frame is used to provide for an extra delay between the preceding and the
succeeding Data or Remote frames.
Data frames and Remote frames are separated from preceding frames by an Interframe space.
Freescale Semiconductor, Inc...
Figure 10-12 at the end of this section summarizes all the frame formats.
10.3.1
Data frame
A Data frame is composed of seven different bit fields: Start of frame, Arbitration field, Control field,
Data field, CRC field, ACKfield, End of frame. The Data field can be of length zero.
Interframe
space
Interframe
space or
Overload
frame
Data frame
Start of
frame
Arbitration
field
Control
field
Data
field
CRC
field
ACK
field
End of
frame
Figure 10-1 Data frame
10.3.1.1
Start of frame
Start of frame marks the beginning of Data frames and Remote frames. It consists of a single
dominant bit.
A node is only allowed to start transmission when the bus is idle (see Section 10.3.5.2). All nodes
have to synchronize to the leading edge caused by Start of frame (see Section 13.9.1) of the node
starting transmission first.
MOTOROLA
10-2
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
79
Freescale Semiconductor, Inc.
10.3.1.2
Arbitration field
Freescale Semiconductor, Inc...
The format of the Arbitration field is different for Standard Format and Extended Format frames.
•
In Standard Format the Arbitration field consists of the 11 bit Identifier and the RTR-Bit. The
Identifier bits are denoted ID-28 ... ID-18.
•
In Extended Format the Arbitration field consists of the 29 bit Identifier, the SRR-Bit, the
IDE-Bit, and the RTR-Bit. The Identifier bits are denoted ID-28 ... ID-0.
Note:
In order to distinguish between Standard Format and Extended Format the reserved bit,
r1, in previous CAN specifications version 1.0-1.2 is now denoted as the IDE bit.
Start of frame
11 Bit Identifier
Data
field
Control
field
Arbitration field
RTR
IDE
r0
DLC
Figure 10-2 Arbitration field; Standard Format
Start of
frame
11 Bit Identifier SRR
IDE 18 Bit Identifier RTR
Data
field
Control
field
Arbitration field
r1
r0
DLC
Figure 10-3 Arbitration field; Extended Format
Identifier
In Standard Format the Identifier’s length is 11 bits and corresponds to the Base ID in Extended
Format. These bits are transmitted in the order from ID-28 to ID-18. The least significant bit is
ID-18. The 7 most significant bits (ID-28 - ID-22) must not be all recessive.
In Extended Format the Identifier’s length is 29 bits. The format comprises two sections; Base ID
with 11 bits and the Extended ID with 18 bits.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
10-3
80
Freescale Semiconductor, Inc.
•
Base ID: The Base ID consists of 11 bits. It is transmitted in the order from ID-28 to ID-18 and
is equivalent to the format of the Standard Identifier. The Base ID defines the Extended Frame’s
base priority.
•
Extended ID: The Extended ID consists of 18 bits. It is transmitted in the order of ID-17 to ID-0.
In a Standard Frame the Identifier is followed by the RTR bit.
Freescale Semiconductor, Inc...
RTR BIT (Standard Format and Extended Format)
Remote Transmission Request bit.
In Data frames the RTR bit has to be dominant. Within a Remote frame the RTR bit has to be
recessive.
In an Extended Frame the Base ID is transmitted first, followed by the IDE bit and the SRR bit. The
Extended ID is transmitted after the SRR bit.
SRR BIT (Extended Format)
Substitute Remote Request bit.
The SRR is a recessive bit. In Extended Frames the SRR bit is transmitted at the position of the
RTR bit in Standard Frames and so substitutes for the RTR bit in the Standard Frame.
As a consequence, collisions between a Standard Frame and an Extended Frame, where the Base
ID (see IDE BIT) of both frames is the same, are resolved in such a way that the Standard Frame
prevails over the Extended Frame.
IDE BIT (Extended Format)
Identifier Extension bit.
The IDE bit belongs to:
•
the Arbitration field for the Extended Format
•
the Control field for the Standard Format
The IDE bit in the Standard Format is transmitted dominant, whereas in the Extended Format the
IDE bit is recessive.
10.3.1.3
Control field
The Control field consists of six bits. The format of the Control field is different for Standard Format
and Extended Format. Frames in Standard Format include the Data length code, the IDE bit, which
is transmitted dominant, and the reserved bit r0. Frames in Extended Format include the Data
length code and two reserved bits, r0 and r1. The reserved bits must be sent dominant, but the
Receivers accept dominant and recessive bits in all combinations.
MOTOROLA
10-4
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
81
Freescale Semiconductor, Inc.
Arbitration
field
IDE/r1
Freescale Semiconductor, Inc...
Data field
or CRC field
Control field
r0
Reserved Bits
Figure 10-4
DLC3
DLC2
DLC1
DLC0
Data length code
Control field; Standard Format and Extended Format
DATA LENGTH CODE (Standard Format and Extended Format)
The number of bytes in the Data field is indicated by the Data length code. This Data length code
is 4 bits wide and is transmitted within the Control field. The DLC bits can code data lengths from
0 to 8 bytes; other values are not permitted.
10.3.1.4
Data field
The Data field consists of the data to be transferred within a Data frame. It can contain from 0 to
8 bytes, each of which contain 8 bits which are transferred MSB first.
Table 10-1 Data length coding
DLC3
d
d
d
d
d
d
d
d
r
CAN PROTOCOL
Rev. 3
DATA LENGTH CODE
DATA BYTE
COUNT
DLC2
DLC1
DLC0
d
d
d
0
d
d
r
1
d
r
d
2
d
r
r
3
r
d
d
4
r
d
r
5
r
r
d
6
r
r
r
7
d
d
d
8
d = dominant
r = recessive
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
10-5
82
Freescale Semiconductor, Inc.
10.3.1.5
CRC field (Standard Format and Extended Format)
The CRC field contains the CRC Sequence followed by a CRC Delimiter.
Freescale Semiconductor, Inc...
Data or
Control field
ACK
field
CRC field
CRC Sequence
CRC Delimiter
Figure 10-5 CRC field
CRC Sequence
The frame check sequence is derived from a cyclic redundancy code best suited to frames with bit
counts less than 127 bits (BCH Code).
In order to carry out the CRC calculation the polynomial to be divided is defined as the polynomial
whose coefficients are given by the destuffed bit-stream consisting of Start of frame, Arbitration
field, Control field, Data field (if present) and, for the 15 lowest coefficients, by 0. This polynomial
is divided (the coefficients are calculated modulo-2) by the generator-polynomial:
X15 + X14 + X10 + X8 + X7 + X4 + X3 + 1
The remainder of this polynomial division is the CRC Sequence transmitted over the bus.
In order to implement this function, a 15-bit shift register CRC_RG(14:0) can be used. If NXTBIT
denotes the next bit of the bit-stream, given by the destuffed bit sequence from Start of frame until
the end of the Data field, the CRC Sequence is calculated as follows:
CRC_RG = 0
//initialize shift register
REPEAT
CRCNXT = NXTBIT EXOR CRC_RG(14)
CRC_RG(14:1) = CRC_RG(13:0)
//shift left by...
CRC_RG(0) = 0
//...one position
IF CRCNXT THEN
CRC_RG(14:0) = CRC_RG(14:0) EXOR (4599 hex)
ENDIF
UNTIL (CRC SEQUENCE starts or there is an ERROR condition)
After the transmission/reception of the last bit of the Data field, CRC_RG(14:0) contains the CRC
Sequence.
CRC Delimiter
The CRC Sequence is followed by the CRC Delimiter which consists of a single recessive bit.
MOTOROLA
10-6
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
83
Freescale Semiconductor, Inc.
10.3.1.6
ACK field (Standard Format and Extended Format)
The ACK field is two bits long and contains the ACK Slot and the ACK Delimiter. In the ACK field
the transmitting node sends two recessive bits.
Freescale Semiconductor, Inc...
A RECEIVER which has received a valid message correctly reports this to the TRANSMITTER by
sending a dominant bit during the ACK Slot (i.e. it sends ACK).
CRC
field
ACK field
ACK Slot
End of
frame
ACK Delimiter
Figure 10-6 ACK field
ACK Slot
All nodes having received the matching CRC Sequence report this within the ACK Slot by
overwriting the recessive bit of the TRANSMITTER by a dominant bit.
ACK Delimiter
The ACK Delimiter is the second bit of the ACK field and has to be a recessive bit. As a
consequence, the ACK Slot is surrounded by two recessive bits (CRC Delimiter, ACK Delimiter).
10.3.1.7
End of frame
Each Data frame and Remote frame is delimited by a flag sequence consisting of seven recessive
bits.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
10-7
84
Freescale Semiconductor, Inc.
10.3.2
Remote frame
A node acting as a RECEIVER for certain data can stimulate the relevant source node to transmit
the data by sending a Remote frame.
Freescale Semiconductor, Inc...
A Remote frame is composed of six different bit fields: Start of frame, Arbitration field, Control field,
CRC field, ACK field, End of frame.
The RTR bit of a Remote frame is always recessive (cf. Data frames where the RTR bit is
dominant).
There is no Data field in a Remote frame, irrespective of the value of the Data length code which
is that of the corresponding Data frame and may be assigned any value within the admissible
range 0... 8.
Interframe
space
Interframe
space or
Overload
frame
Remote frame
Start of
frame
Arbitration
field
Control
field
CRC
field
ACK
field
End of
frame
Figure 10-7 Remote frame
The polarity of the RTR bit indicates whether a transmitted frame is a Data frame (RTR bit
dominant) or a Remote frame (RTR bit recessive).
10.3.3
Error frame
The Error frame consists of two distinct fields. The first field is given by the superposition of Error
flags contributed from different nodes. The second field is the Error Delimiter.
In order to terminate an Error frame correctly, an error-passive node may need the bus to be
bus-idle for at least three bit times (if there is a local error at an error-passive receiver). Therefore
the bus should not be loaded to 100%.
MOTOROLA
10-8
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
85
Freescale Semiconductor, Inc.
Data
frame
Interframe space
or
Overload frame
Error frame
Error flag
Error Delimiter
Freescale Semiconductor, Inc...
Superposition of
Error flags
Figure 10-8 Error frame
10.3.3.1
Error flag
There are two forms of error flag: an ACTIVE Error flag and a PASSIVE Error flag.
1) ACTIVE Error flag consists of six consecutive dominant bits.
2) The PASSIVE Error flag consists of six consecutive recessive bits unless it
is overwritten by dominant bits from other nodes.
An error-active node detecting an error condition signals this by the transmission of an ACTIVE
Error flag. The Error flag’s form violates the law of bit stuffing (see Section 10.7), applied to all
fields from Start of frame to CRC Delimiter, or destroys the fixed form ACK field or End of frame
field. As a consequence, all other nodes detect an error condition and each starts to transmit an
Error flag. So the sequence of dominant bits which actually can be monitored on the bus results
from a superposition of different Error flags transmitted by individual nodes. The total length of this
sequence varies between a minimum of six and a maximum of twelve bits.
An error-passive node detecting an error condition tries to signal this by transmitting a PASSIVE
Error flag. The error-passive node waits for six consecutive bits of equal polarity, beginning at the
start of the PASSIVE Error flag. The PASSIVE Error flag is complete when these six equal bits have
been detected.
10.3.3.2
Error delimiter
The Error Delimiter consists of eight recessive bits.
After transmission of an Error flag each node sends recessive bits and monitors the bus until it
detects a recessive bit. Afterwards it starts transmitting seven more recessive bits.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
10-9
86
Freescale Semiconductor, Inc.
10.3.4
Overload frame
The Overload frame contains two bit fields, Overload flag and Overload Delimiter.
There are three kinds of Overload condition which lead to the transmission of an Overload flag:
1) Where the internal conditions of a receiver are such that the receiver
requires a delay of the next Data frame or Remote frame.
Freescale Semiconductor, Inc...
2) On detection of a dominant bit during INTERMISSION.
3) If a CAN node samples a dominant bit at the eighth bit (i.e. the last bit) of an
Error Delimiter or Overload Delimiter, it will start transmitting an Overload
frame (not an Error frame). The Error Counters will not be incremented.
An Overload frame resulting from Overload condition 1 is only allowed to start at the first bit time
of an expected INTERMISSION, whereas Overload frames resulting from Overload conditions 2
and 3 start one bit after detecting the dominant bit.
End of frame or
Error Delimiter or
Overload Delimiter
Interframe space
or
Overload frame
Overload frame
Overload flag
Overload Delimiter
Superposition of
Overload flags
Figure 10-9 Overload frame
At most, two Overload frames may be generated to delay the next Data frame or Remote frame.
MOTOROLA
10-10
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
87
Freescale Semiconductor, Inc.
10.3.4.1
Overload flag
Freescale Semiconductor, Inc...
The Overload flag consists of six dominant bits. The overall form corresponds to that of the ACTIVE
Error flag.
The Overload flag’s form destroys the fixed form of the INTERMISSION field. As a consequence,
all other nodes also detect an Overload condition and each starts to transmit an Overload flag. In
the event that there is a dominant bit detected during the third bit of INTERMISSION, then it will
interpret this bit as Start of frame.
Note:
Controllers based on the CAN Specification version 1.0 and 1.1 interpret the of third bit
of INTERMISSION in a different way. If the dominant bit was detected locally at some
node, the other nodes will not interpret the Overload flag correctly, but will interpret the
first of these six dominant bits as Start of frame; the sixth of these dominant bits violates
the rule of bit stuffing causing an error condition.
10.3.4.2
Overload delimiter
The Overload Delimiter consists of eight recessive bits.
The Overload Delimiter is of the same form as the Error Delimiter. After transmission of an
Overload flag the node monitors the bus until it detects a transition from a dominant to a recessive
bit. At this point of time every bus node has finished sending its Overload flag and all nodes start
transmission of seven more recessive bits in coincidence.
10.3.5
Interframe space
Data frames and Remote frames are separated from preceding frames, whatever type they may
be (Data frame, Remote frame, Error frame, Overload frame), by a field called Interframe space.
In contrast, Overload frames and Error frames are not preceded by an Interframe space and
multiple Overload frames are not separated by an Interframe space.
The Interframe space contains the bit fields INTERMISSION and Bus idle and, for error- passive
nodes, which have been the transmitter of the previous message, SUSPEND TRANSMISSION
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
10-11
88
Freescale Semiconductor, Inc.
(1) For nodes which are not error-passive or have been a receiver of the previous message, see
Figure 10-10 and Figure 10-12 (page 1 of 2).
Interframe space
Freescale Semiconductor, Inc...
Frame
Intermission
Frame
Bus Idle
Figure 10-10 Interframe space (1)
(2) For error-passive nodes which have been the transmitter of the previous message, see
Figure 10-11 and Figure 10-12 (page 2 of 2).
Interframe space
Frame
Intermission
Suspend
Transmission
Figure 10-11
10.3.5.1
Frame
Bus Idle
Interframe space (2)
INTERMISSION
INTERMISSION consists of three recessive bits.
During INTERMISSION no node is allowed to start transmission of a Data frame or Remote frame.
The only action permitted is signalling of an Overload condition.
Note:
If a CAN node has a message waiting for transmission and it samples a dominant bit at
the third bit of INTERMISSION, it will interpret this as a Start of frame bit. With the next
bit, it will start transmitting its message with the first bit of its Identifier without first
transmitting a Start of frame bit and without becoming Receiver.
MOTOROLA
10-12
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
89
Freescale Semiconductor, Inc.
10.3.5.2
Bus idle
The period of Bus idle may be of arbitrary length. The bus is recognized to be free, and any node
having something to transmit can access the bus. A message, pending during the transmission of
another message, is started in the first bit following INTERMISSION.
Freescale Semiconductor, Inc...
The detection of a dominant bit on the bus is interpreted as Start of frame.
10.3.5.3
Suspend transmission
After an error-passive node has transmitted a frame, it sends eight recessive bits following
INTERMISSION, before starting to transmit a further message or recognizing the bus to be idle.
If, meanwhile, a transmission (caused by another node) starts, the node will become the receiver
of this message.
10.4
Conformance with regard to frame formats
The Standard Format is equivalent to the Data/Remote frame Format as it is described in the CAN
Specification 1.2. In contrast the Extended Format is a new feature of the CAN protocol. In order
to allow the design of relatively simple controllers, the implementation of the Extended Format to
its full extend is not required (e.g. send messages or accept data from messages in Extended
Format), whereas the Standard Format must be supported without restriction.
New controllers are considered to be in conformance with this CAN Specification, if they have at
least the following properties with respect to the Frame Formats defined in Section 10.2 and
Section 10.3:
•
Every new controller supports the Standard Format
•
Every new controller can receive messages of the Extended Format. This requires that
Extended frames are not destroyed just because of their format. It is, however, not required that
the Extended Format must be supported by new controllers.
10.5
Message filtering
Message filtering is based upon the whole Identifier. Optional mask registers that allow any
Identifier bit to be set ’don’t care’ for message filtering, may be used to select groups of Identifiers
to be mapped into the attached receive buffers.
If mask registers are implemented every bit of the mask registers must be programmable, i.e. they
can be enabled or disabled for message filtering. The length of the mask register can comprise the
whole Identifier or only part of it.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
10-13
90
CAN PROTOCOL
Rev. 3
16
CRC Þeld
8
8
15
CRC
IdentiÞer
Acceptance
Þltering
Reserved bits
d d d
CRC Del
Acknowledge
Ack Del
4
DLC0
11
8N (0 ≤ N ≤ 8)
Data Þeld
6
Control Þeld
ID18
RTR
IDE
RB0
DLC3
Start of frame
ID28
12
Arbitration Þeld
d
r
7
End of frame
r r r r r r r r
Data
length
code
Stored in transmit/receive buffers
Stored in buffers
Bit stufÞng
d
r d d
4
DLC0
11
6
Control Þeld
I18
RTR
IDE
RB0
DLC3
12
Arbitration Þeld
16
CRC Þeld
15
CRC
CRC Del
Acknowledge
Ack Del
(number of bits = 44)
Remote frame
Start of frame
ID28
Figure 10-12 CAN frame format - Standard Format (Page 1 of 2)
MESSAGE TRANSFER
Freescale Semiconductor, Inc...
MOTOROLA
10-14
(number of bits = 44 + 8N)
Data frame
r
7
End of frame
r r r r r r r r
Note:
A remote frame is identical to a data
frame, except that the RTR bit is
recessive, and there is no data Þeld.
91
Data frame
or
remote frame
≤6
Echo
error ßag
6
Error ßag
d d d d d d d
8
Inter-frame space
or
overload frame
Error delimiter
Inter-frame space
3
Any frame
8
Suspend
transmit
INT
Note:
An error frame can start anywhere in the
middle of a frame.
Note:
INT = Intermission
Suspend transmission is only for error
passive nodes.
Note:
An overload frame can only start at the end
of a frame.
Maximum echo of overload ßag is one bit.
d d r r r r r r r r
Bus idle
r r r r r r r r r r r r r r r r r r r r
Start of frame
Freescale Semiconductor, Inc...
MESSAGE TRANSFER
Figure 10-12 CAN frame format - Standard Format (Page 2 of 2)
CAN PROTOCOL
Rev. 3
Error frame
Data frame
or
remote frame
r r r d
Overload frame
End of frame
or
error delimiter
or
overload delimiter
6
8
Overload ßag
Overload delimiter
d d d d d d d r r r r r r r r
Inter-frame space
or
error frame
MOTOROLA
10-15
92
8N (0 ≤ N ≤ 8)
Data Þeld
8
8
15
CRC
DLC0
4
16
CRC Þeld
IdentiÞer
Acceptance
Þltering
Reserved bits
d d d
IdentiÞer
r
Data
length
code
Stored in transmit/receive buffers
Stored in buffers
Bit stufÞng
Remote frame
6
Control Þeld
4
ID0
RTR
IDE
RB0
DLC3
ID18
SRR
IDE
ID17
18
d
r d d
CAN PROTOCOL
Rev. 3
Note:
DLC0
11
(number of bits = 64)
16
CRC Þeld
15
CRC
CRC Del
Acknowledge
Ack Del
32
Arbitration Þeld
CRC Del
Acknowledge
Ack Del
18
ID0
RTR
RB1
RB0
DLC3
11
(number of bits = 64 + 8N)
6
Control Þeld
ID18
SRR
IDE
ID17
Start of frame
ID28
32
Arbitration Þeld
d
Start of frame
ID28
Figure 10-13 CAN frame format - Extended Format
MESSAGE TRANSFER
Freescale Semiconductor, Inc...
MOTOROLA
10-16
Data frame
r
7
End of frame
r r r r r r r r
A remote frame is identical to a data frame, except that the
RTR bit is recessive, and there is no data Þeld.
7
End of frame
r r r r r r r r
93
Freescale Semiconductor, Inc.
10.6
Message validation
The point in time at which a message is taken to be valid is different for the transmitter and the
receivers of the message.
Freescale Semiconductor, Inc...
10.6.1
Transmitter
The message is valid for the transmitter if there is no error until the End of frame. If a message is
corrupted, retransmission will follow automatically and according to the rules of prioritization. In
order to be able to compete for bus access with other messages, retransmission has to start as
soon as the bus is idle.
10.6.2
Receiver
The message is valid for the receiver if there is no error until the last but one bit of End of frame.
10.7
Bit-stream coding
The frame segments Start of frame, Arbitration field, Control field, Data field and CRC Sequence
are coded by the method of bit stuffing. Whenever a transmitter detects five consecutive bits of
identical value in the bit-stream to be transmitted, it automatically inserts a complementary bit in
the actual transmitted bit-stream.
The remaining bit fields of the Data frame or Remote frame(CRC Delimiter, ACK field and End of
frame) are of fixed form and not stuffed.
The Error frame and the Overload frame are also of fixed form and are not coded by the method
of bit stuffing.
The bit-stream in a message is coded according to the Non-Return-to-Zero (NRZ) method. This
means that during the total bit time the generated bit level is either dominant or recessive.
CAN PROTOCOL
Rev. 3
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
10-17
94
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
THIS PAGE LEFT BLANK INTENTIONALLY
MOTOROLA
10-18
MESSAGE TRANSFER
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
95
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
11
ERROR HANDLING
11.1
Error detection
There are five different error types (which are not mutually exclusive). The following sections
describe these errors.
11.1.1
Bit error
A node which is sending a bit on the bus also monitors the bus. The node must detect, and interpret
as a Bit Error, the situation where the bit value monitored is different from the bit value being sent.
An exception to this is the sending of a recessive bit during the stuffed bit-stream of the Arbitration
Field or during the ACK Slot; in this case no Bit Error occurs when a dominant bit is monitored.
A transmitter sending a PASSIVE Error Flag and detecting a dominant bit does not interpret this
as a Bit Error.
11.1.2
11
Stuff error
A Stuff Error must be detected and interpreted as such at the bit time of the sixth consecutive equal
bit level (6 consecutive dominant or 6 consecutive recessive levels), in a message field which
should be coded by the method of bit stuffing.
11.1.3
CRC error
The CRC sequence consists of the result of the CRC calculation by the transmitter.
The receivers calculate the CRC in the same way as the transmitter. A CRC Error must be
recognized if the calculated result is not the same as that received in the CRC sequence.
CAN PROTOCOL
Rev. 3
ERROR HANDLING
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
11-1
96
Freescale Semiconductor, Inc.
11.1.4
Form error
A Form Error must be detected when a fixed-form bit field contains one or more illegal bits.
Freescale Semiconductor, Inc...
Note:
11
For a Receiver, a dominant bit during the last bit of End of Frame is not treated as Form
Error.
11.1.5
Acknowledgement error
An Acknowledgement Error must be detected by a transmitter whenever it does not monitor a
dominant bit during ACK Slot.
11.2
Error signalling
A node detecting an error condition signals this by transmitting an Error Flag. An error-active node
will transmit an ACTIVE Error Flag; an error-passive node will transmit a PASSIVE Error Flag.
Whenever a Bit Error, a Stuff Error, a Form Error or an Acknowledgement Error is detected by any
node, that node will start transmission of an Error Flag at the next bit time.
Whenever a CRC Error is detected, transmission of an Error Flag will start at the bit following the
ACK Delimiter, unless an Error Flag for another error condition has already been started.
MOTOROLA
11-2
ERROR HANDLING
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
97
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
12
FAULT CONFINEMENT
12.1
CAN node status
With respect to fault confinement, a node may be in one of three states: error-active, error-passive,
or bus-off.
An error active node can normally take part in bus communication and sends an ACTIVE Error
Flag when an error has been detected.
An error-passive node must not send an ACTIVE Error Flag. It takes part in bus communication,
but when an error has been detected only a PASSIVE Error Flag is sent. Also after a transmission,
an error-passive node will wait before initiating a further transmission.
A bus-off node is not allowed to have any influence on the bus (e.g. output drivers switched off).
12.2
12
Error counts
To facilitate fault confinement two counts are implemented in every bus node:
•
TRANSMIT ERROR COUNT
•
RECEIVE ERROR COUNT
These counts are modified according to the following 12 rules:
Note:
More than one rule may apply during a given message transfer
1) When a RECEIVER detects an error, the Receive Error Count will be
increased by 1, except when the detected error was a Bit Error during the
sending of an ACTIVE Error Flag or an Overload Flag.
2) When a RECEIVER detects a dominant bit as the first bit after sending an
Error Flag, the Receive Error Count will be increased by 8.
TPG
CAN PROTOCOL
Rev. 3
FAULT CONFINEMENT
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
12-1
98
Freescale Semiconductor, Inc.
3) When a TRANSMITTER sends an Error Flag, the Transmit Error Count is
increased by 8.
Exception 1
The Transmit Error Countis not changed if:
–
The TRANSMITTER is error-passive
Freescale Semiconductor, Inc...
and
12
–
the TRANSMITTER detects an Acknowledgement Error because of not
detecting a dominant”ACK
and
–
the TRANSMITTER does not detect a dominant bit while sending its
PASSIVE Error Flag
Exception 2
The Transmit Error Count is not changed if:
–
The TRANSMITTER sends an Error Flag because a Stuff Error occurred
during Arbitration
and
–
the Stuff bit should have been recessive
and
–
the Stuff Bit has been sent as recessive but is monitored as dominant
4) An error-active TRANSMITTER detects a Bit Error while sending an ACTIVE
Error Flag or an Overload Flag, the Transmit Error Count is increased by 8.
5) An error-active RECEIVER detects a bit error while sending an ACTIVE
Error Flag or an Overload Flag, the Receive Error Count is increased by 8.
6) Any node tolerates up to 7 consecutive dominant bits after sending an
ACTIVE Error Flag or a PASSIVE Error Flag. After detecting the eighth
consecutive dominant bit and after each sequence of additional eight
consecutive dominant bits, every TRANSMITTER increases its Transmit
Error Count by 8 and every RECEIVER increases its Receive Error Count by
8.
7) After the successful transmission of a message (getting ACK and no error
until End of Frame is finished), the Transmit Error Count is decreased by 1,
unless it was already 0.
8) After the successful reception of a message (reception without error up to
the ACK Slot and the successful sending of the ACK bit), the Receive Error
TPG
MOTOROLA
12-2
FAULT CONFINEMENT
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
99
Freescale Semiconductor, Inc.
Count is decreased by 1, if it was between 1 and 127. If the Receive Error
Count was 0, it stays 0, and if it was greater than 127, then it will be set to a
value between 119 and 127.
Freescale Semiconductor, Inc...
9) A node is error passive when the Transmit Error Count equals or exceeds
128, or when the Receive Error Count equals or exceeds 128. An error
condition letting a node become error-passive causes the node to send an
ACTIVE Error Flag.
10) A node is bus-off when the Transmit Error Count is greater than or equal to
256.
11) An error-passive node becomes error-active again when both the Transmit
Error Count and the Receive Error Countare less than or equal to 127.
12) A node which is bus-off is permitted to become error-active (no longer
bus-off) with its error counters both set to 0 after 128 occurrences of 11
consecutive recessive bits have been monitored on the bus.
Note:
An error count value greater than about 96 indicates a heavily disturbed bus. It may be
advantageous to provide the means to test for this condition.
Note:
Start-up/Wake-up
If during system start-up only one node is on line, and if this node transmits some
message, it will get no acknowledgement, detect an error and repeat the message. It
can become error-passive but not bus-off due to this reason.
12
TPG
CAN PROTOCOL
Rev. 3
FAULT CONFINEMENT
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
12-3
100
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
THIS PAGE LEFT BLANK INTENTIONALLY
12
TPG
MOTOROLA
12-4
FAULT CONFINEMENT
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
101
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
13
BIT TIMING REQUIREMENTS
13.1
Nominal bit rate
The Nominal bit rate is the number of bits per second transmitted in the absence of
resynchronization by an ideal transmitter.
13.2
Nominal bit time
1
NOMINAL BIT TIME = -------------------------------------------------------NOMINAL BIT RATE
The Nominal bit time can be thought of as being divided into separate non-overlapping time
segments. These segments are as shown below, and form the bit time as shown in Figure 13-1.
•
SYNCHRONIZATION SEGMENT (SYNC_SEG)
•
PROPAGATION TIME SEGMENT (PROP_SEG)
•
PHASE BUFFER SEGMENT1 (PHASE_SEG1)
•
PHASE BUFFER SEGMENT2 (PHASE_SEG2)
13
Nominal bit time
SYNC_SEG
PROP_SEG
PHASE_SEG1
PHASE_SEG2
Sample point
Figure 13-1 Nominal bit time
CAN PROTOCOL
Rev. 3
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
13-1
102
Freescale Semiconductor, Inc.
13.3
SYNC_SEG
This part of the bit time is used to synchronize the various nodes on the bus. An edge is expected
to lie within this segment
Freescale Semiconductor, Inc...
13.4
13
PROP_SEG
This part of the bit time is used to compensate for the physical delay times within the network. It is
twice the sum of the signal’s propagation time on the bus line, the input comparator delay, and the
output driver delay.
13.5
PHASE_SEG1, PHASE_SEG2
These Phase-Buffer-Segments are used to compensate for edge phase errors. These segments
can be lengthened or shortened by resynchronization.
13.6
Sample point
The Sample point is the point in time at which the bus level is read and interpreted as the value of
that respective bit. Its location is at the end of PHASE_SEG1.
13.7
Information processing time
The Information processing time is the time segment starting with the Sample point reserved for
calculation of the subsequent bit level.
13.8
Time quantum
The Time quantum is a the fixed unit of time which can be derived from the oscillator period. There
is a programmable prescaler, with integral values (with a range of at least 1 to 32) which allows a
fixed unit of time, the Time quantum can have a length of
TIME QUANTUM = m × MINIMUM TIME QUANTUM
where m is the value of the prescaler.
MOTOROLA
13-2
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
103
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
13.8.1
Length of time segments
•
SYNC_SEG is 1 Time quantum long
•
PROP_SEG is programmable to be 1, 2, ......8 Time quanta long
•
PHASE_SEG1 is programmable to be 1, 2, ......8 Time quanta long
•
PHASE_SEG2 is the maximum of PHASE_SEG1 and the Information processing time
•
The Information processing time is less than or equal to 2 Time quanta long
The total number of Time quanta in a bit time must be programmable over a range of at least 8 to
25.
Note:
Control units normally do not use different oscillators for the local CPU and its
communication device. Therefore the oscillator frequency of a CAN device tends to be
that of the local CPU and is determined by the requirements of the control unit. In order
to derive the desired bit rate, programmability of the bit timing is necessary. In the case
of CAN implementations that are designed for use without a local CPU the bit timing
cannot be programmable. However, these devices allow the choice of an external
oscillator in such a way that the device is adjusted to the appropriate bit rate so that the
programmability is dispensable for such components. The position of the sample point,
however, should be selected in common for all nodes. Therefore the bit timing of CAN
devices without a local CPU must be compatible with the following definition of the bit
time.
SYNC PROP
SEG
SEG
1 Time
quantum
1 Time
quantum
Phase Buffer Seg 1
Phase Buffer Seg 2
4 Time quanta
4 Time quanta
13
1 Bit time
10 Time quanta
Figure 13-2 Bit timing of CAN devices without local CPU
CAN PROTOCOL
Rev. 3
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
13-3
104
Freescale Semiconductor, Inc.
13.9
Synchronization
13.9.1
Hard synchronization
Freescale Semiconductor, Inc...
After a Hard synchronization the internal bit time is restarted with SYNC_SEG. Thus Hard
synchronization forces the edge which has caused the Hard synchronization to lie within the
Synchronization segment of the restarted bit time.
13
13.9.2
Resynchronization jump width
As a result of resynchronization, PHASE_SEG1 may be lengthened or PHASE_SEG2 may be
shortened. The amount by which the Phase buffer segments may be altered may not be greater
than the Resynchronization jump width. The Resynchronization jump width is programmable
between 1 and the smaller of 4 and PHASE_SEG1 Time quanta.
Clocking information may be derived from transitions from one bit value to the other. The property
that only a fixed maximum number of successive bits have the same value provides the possibility
of resynchronising a bus node to the bit-stream during a frame.
The maximum length between two transitions which can be used for resynchronization is 29 bit
times.
13.9.3
Phase error of an edge
The Phase error of an edge is given by the position of the edge relative to SYNC_SEG, measured
in Time quanta. The sign of Phase error is defined as follows:
e
< 0
if the edge lies after the Sample point of the previous bit,
e
= 0
if the edge lies within SYNC_SEG,
e
> 0
if the edge lies before the Sample point.
13.9.4
Resynchronization
The effect of a Resynchronization is the same as that of Hard synchronization, when the
magnitude of the Phase error of the edge which causes the Resynchronization is less than or
equal to the programmed value of the Resynchronization jump width.
When the magnitude of the Phase error is larger than the Resynchronization jump width, and if the
Phase error is positive, then PHASE_SEG1 is lengthened by an amount equal to the
Resynchronization jump width.
MOTOROLA
13-4
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
105
Freescale Semiconductor, Inc.
When the magnitude of the Phase error is larger than the Resynchronization jump width, and if the
Phase error is negative, then PHASE_SEG2 is shortened by an amount equal to the
Resynchronization jump width.
Freescale Semiconductor, Inc...
13.9.5
Synchronization rules
Hard synchronization and Resynchronization are the two forms of Synchronization. They obey the
following rules:
1) Only one Synchronization within one bit time is allowed.
2) An edge will be used for Synchronization only if the value detected at the
previous Sample point (previous read bus value) differs from the bus value
immediately after the edge.
3) Hard synchronization is performed whenever there is a recessive to
dominant edge during Bus idle.
4) All other recessive to dominant edges (and optionally dominant to recessive
edges in the case of low bit rates) fulfilling the rules 1 and 2 will be used for
Resynchronization with the exception that a transmitter will not perform a
Resynchronization as a result of a recessive to dominant edge with a
positive Phase error, if only recessive to dominant edges are used for
Resynchronization.
13
CAN PROTOCOL
Rev. 3
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
13-5
106
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
THIS PAGE LEFT BLANK INTENTIONALLY
13
MOTOROLA
13-6
BIT TIMING REQUIREMENTS
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
107
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
A
THE MOTOROLA CAN (MCAN) MODULE
A.1
Functional overview
The MCAN includes all hardware modules necessary to implement the CAN Transfer Layer, which
represents the kernel of the CAN bus protocol as defined by BOSCH GmbH, the originators of the
CAN specification.
Up to the message level, the MCAN is totally compatible with CAN Specification 2.0 Part A.
Functional differences are related to the object layer only. Whereas a full CAN controller provides
dedicated hardware for handling a set of messages, the MCAN is restricted to receiving and/or
transmitting messages on a message by message basis.
The MCAN will never initiate an Overload Frame. If the MCAN starts to receive a valid message
(one that passes the Acceptance Filter) and there is no receive buffer available for it then the
Overrun Flag in the CPU Status register will be set. The MCAN will respond to Overload Frames
generated by other CAN nodes, as required by the CAN protocol.
A diagram of the major blocks of the MCAN is shown in Figure A-1.
A.1.1
IML – interface management logic
The IML interprets the commands from the CPU, controls the allocation of the message buffers
TBF, RBF0 and RBF1, and supplies interrupts and status information to the CPU via the Controller
Interface Logic (CIL).
A
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-1
108
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Interface
Management
Logic
CPU
INTERFACE
Bit Timing
Logic
(BTL)
Line
Interface
Logic
(IML)
Transceive
Logic
(TCL)
Transmit
Buffer
(TBF)
Error
Management
Logic
(EML)
CAN
BUS
LINE
Receive
Buffer #0
(RBF0)
Bit Stream
Processor
(BSP)
Receive
Buffer #1
(RBF1)
Microprocessor related Logic
Bus Line related Logic
Figure A-1 MCAN module block diagram
A
TPG
MOTOROLA
A-2
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
109
Freescale Semiconductor, Inc.
A.1.2
TBF – transmit buffer
Freescale Semiconductor, Inc...
The transmit buffer is an interface between the CPU and the Bit Stream Processor (BSP) and is
able to store a complete message. The buffer is written by the CPU and read by the BSP. The CPU
may access this buffer whenever TRANSMIT BUFFER ACCESS is set to released. On requesting
a transmission, by setting TRANSMISSION REQUEST in the CAN COMMAND REGISTER =
present, TRANSMIT BUFFER ACCESS is set to locked, giving the BSP exclusive access to this
buffer. The transmit buffer is released after the message transfer has been completed or aborted.
The TBF is 10 bytes long and holds the Identifier (1 byte), the Control Field (1 byte) and the Data
Field (maximum length 8 bytes). The buffer is implemented as a single-ported RAM, with mutual
exclusive access by the CPU and the BSP.
A.1.3
RBF – receive buffer
The receive buffer is an interface between the BSP and the CPU and stores a message received
from the bus line. Once filled by the BSP and allocated to the CPU by the IML, the receive buffer
cannot be used to store subsequent received messages until the CPU has acknowledged the
reading of the buffer’s contents. Thus, unless the CPU releases an RBF within a protocol defined
time frame, future messages to be received may be lost.
To reduce the requirements on the CPU, two receive buffers (RBF0 and RBF1) are implemented.
While one receive buffer is allocated to the CPU, the BSP may write to the other buffer. RBF0 and
RBF1 are each 10 bytes long and hold the Identifier (1 byte), the Control Field(1 byte) and the Data
Field(maximum length 8 bytes). The buffers are implemented as single-ported RAMs with mutual
exclusive access from the CPU and the BSP. The BSP only writes into a receive buffer when the
message being received or transmitted has an Identifier which passes the Acceptance Filter. Note
that a message being transmitted will be written to the receive buffer if its Identifier passes the
Acceptance Filter, as it cannot be known until after the first byte has been stored whether or not
the message will lose arbitration to another transmitter.
A.1.4
BSP – bit stream processor
This is a sequencer controlling the data stream between the transmit and receive buffers (parallel
data) and the bus line (serial data). The BSP also controls the Transceive Logic (TCL) and the Error
Management Logic (EML) such that the processes of reception, arbitration, transmission and error
signalling are performed according to the protocol and the bus rules. The BSP also provides
signals to the IML indicating when a receive buffer contains a valid message and also when the
transmit buffer is no longer required after a successful transmission. Note that the automatic
retransmission of messages which have been corrupted by noise or other external error conditions
on the bus line is effectively handled by the BSP.
A
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-3
110
Freescale Semiconductor, Inc.
A.1.5
BTL – bit timing logic
Freescale Semiconductor, Inc...
This block monitors the bus line using the INPUT COMPARATOR and handles the bus line related
bit timing.
The BTL synchronizes on a recessive to dominant bus line transition at the Start of Frame (hard
synchronization), and resynchronizes on further transitions during a reception of a frame (soft
synchronization). A CPU programmable control bit (SPEED MODE) determines which edges are
used for resynchronization.
The BTL also provides programmable time segments to compensate for the propagation delay
times and phase shifts and to define the sampling time and the number of samples (1 or 3) within
the bus time slot.
A.1.6
TCL – transceive logic
The TCL is a generic term for a group of logic elements consisting of a programmable output driver,
bit stuff logic, CRC logic and the transmit shift register. The coordination of these components is
controlled by the BSP.
A.1.7
EML – error management logic
The EML is responsible for the error confinement of the MCAN Module. It receives notification of
errors from the BSP and then informs the BSP, TCL and IML about error statistics.
Note:
The BSP, TCL, BTL and EML together are described collectively as the bus line related
logic. Similarly, the IML, CIL, TBF, RBF0 and RBF1 are described as microprocessor
related logic.
A
TPG
MOTOROLA
A-4
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
111
Freescale Semiconductor, Inc.
A.2
MCAN interface
Freescale Semiconductor, Inc...
To be able to function as a serial communication interface, the MCAN Module itself has to be
supplemented by an additional module, the Controller Interface Unit (CIL).
Control
CPU
Address/Data
Control
CPU
Interface
Logic
clock
Address/Data
MCAN
Module
clock
Figure A-2 Block diagram of the MCAN interface
A.2.1
CIL – controller interface unit
The CIL links the MCAN Module to the CPU. It connects the CPU buses to the 8-bit MCAN buses.
It also generates internal MCAN control signals from internal CPU signals.
The CIL receives the various signals for wake-up/sleep inhibit from the rest of the circuit and the
go to sleep signal from the IML
A
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-5
112
Freescale Semiconductor, Inc.
A.2.2
Address allocation
MCAN register blocks
MCAN registers
$0020
Freescale Semiconductor, Inc...
MCAN
control registers
10 bytes
$0029
$002A
MCAN
transmit buffer
10 bytes
$0033
$0034
MCAN
receive buffer
10 bytes
$003D
Control register
$0020
Command register
$0021
Status register
$0022
Interrupt register
$0023
Acceptance code register
$0024
Acceptance mask register
$0025
Bus timing register 1
$0026
Bus timing register 2
$0027
Output control register
$0028
Test register
$0029
IdentiÞer
$002A
RTR-bit, data length code
$002B
Data segment byte 1
$002C
Data segment byte 2
$002D
Data segment byte 3
$002E
Data segment byte 4
$002F
Data segment byte 5
$0030
Data segment byte 6
$0031
Data segment byte 7
$0032
Data segment byte 8
$0033
IdentiÞer
$0034
RTR-bit, data length code
$0035
Data segment byte 1
$0036
Data segment byte 2
$0037
Data segment byte 3
$0038
Data segment byte 4
$0039
Data segment byte 5
$003A
Data segment byte 6
$003B
Data segment byte 7
$003C
Data segment byte 8
$003D
Figure A-3 MCAN module memory map
A
TPG
MOTOROLA
A-6
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
113
Freescale Semiconductor, Inc.
A.2.3
Control registers
The interchange of commands, status and control signals between the CPU and the MCAN
Module takes place via the control registers. The layout of these registers is shown in Figure A-3.
Freescale Semiconductor, Inc...
Note:
The acceptance code register, acceptance mask register, bus timing register 0, bus
timing register 1 and the output control register are only accessible when the RESET
REQUEST bit in the MCAN control register is set to present. It is not foreseen that these
registers will be referenced again after the initial reset sequence.
Table A-1 Control registers
Register
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
Control (CCNTRL)
$0020
MODE
SPD
OIE
EIE
TIE
RIE
RR
COMP-SEL SLEEP
Command (CCOM )
$0021
RX0
RX1
COS
RRB
AT
TR
Status (CSTAT)
$0022
BS
ES
TS
RS
TCS
TBA
DO
RBS
Interrupt (CINT)
$0023
WIF
OIF
EIF
TIF
RIF
Acceptance code (CACC)
$0024
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
Acceptance mask (CACM)
$0025
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
Bus timing 0 (CBTO)
$0026
SJW1
SJW0
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0
Bus timing 1 (CBT1)
$0027
SAMP TSEG-22 TSEG-21 TSEG-20 TSEG13 TSEG-12 TSEG-11 TSEG-10
Output control (COCNTRL)
$0028
OCT-P1 OCT-N1 OCPOL1 OCT-P0 OCT-N0 OCPOL0 OCM1
OCM0
A.2.4
MCAN control register (CCNTRL)
This register may be read or written to by the MCU; only the RR bit is affected by the MCAN.
Address
MCAN control (CCNTRL)
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
OIE
EIE
TIE
RIE
RR
Reset
condition
State
on reset
External reset 0u - u uuu1
$0020 MODE SPD
RR bit set
0u - u uuu1
MODE — Undefined mode
This bit must never be set by the CPU as this would result in the transmit and receive buffers being
mapped out of memory. The bit is cleared on reset, and should be left in this state for normal
operation.
A
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-7
114
Freescale Semiconductor, Inc.
SPD — Speed mode
1 (set)
–
0 (clear) –
Slow – Bus line transitions from both recessive to dominant and from
dominant to recessive will be used for resynchronization.
Fast – Only transitions from recessive to dominant will be used for
resynchronization.
Freescale Semiconductor, Inc...
OIE — Overrun interrupt enable
A
1 (set)
–
0 (clear) –
Enabled – The CPU will get an interrupt request whenever the
Overrun Status bit gets set.
Disabled – The CPU will get no overrun interrupt request.
EIE — Error interrupt enable
1 (set)
–
0 (clear) –
Enabled – The CPU will get an interrupt request whenever the error
status or bus status bits in the CSTAT register change.
Disabled – The CPU will get no error interrupt request.
TIE — Transmit interrupt enable
1 (set)
–
0 (clear) –
Enabled – The CPU will get an interrupt request whenever a
message has been successfully transmitted, or when the transmit
buffer is accessible again following an ABORT command.
Disabled – The CPU will get no transmit interrupt request.
RIE — Receive interrupt enable
1 (set)
–
0 (clear) –
Enabled – The CPU will get an interrupt request whenever a
message has been received free of errors.
Disabled – The CPU will get no receive interrupt request.
RR — Reset request
When the MCAN detects that RR has been set it aborts the current transmission or reception of a
message and enters the reset state. A reset request may be generated by either an external reset
or by the CPU or by the MCAN. The RR bit can be cleared only by the CPU. After the RR bit has
been cleared, the MCAN will start normal operation in one of two ways. If RR was generated by
an external reset or by the CPU, then the MCAN starts normal operation after the first occurrence
of 11 recessive bits. If, however, the RR was generated by the MCAN due to the BS bit being set
(see Section A.2.6) the MCAN waits for 128 occurrences of 11 recessive bits before starting
normal operation.
TPG
MOTOROLA
A-8
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
115
Freescale Semiconductor, Inc.
A reset request should not be generated by the CPU during a message transmission. Ensure that
a message is not being transmitted as follows:
if TCS in CSTAT is clear – set AT in CCOM (use STA or STX), read CSTAT.
if TS in CSTAT is set – wait until TS is clear.
Freescale Semiconductor, Inc...
Note that a CPU-generated reset request does not change the values in the transmit and receive
error counters.
1 (set)
–
0 (clear) –
Note:
Present – MCAN will be reset.
Absent – MCAN will operate normally.
The following registers may only be accessed when reset request = present: CACC,
CACM, CBT0, CBT1, and COCNTRL.
A.2.5
MCAN command register (CCOM)
This is a write only register; a read of this location will always return the value $FF.
This register may be written only when the RR bit in CCNTRL is clear.
Do not use read-modify-write instructions on this register (e.g. BSET, BCLR).
Address
MCAN command (CCOM) $0021
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
RX0
RX1 COMPSEL SLEEP COS
RRB
AT
TR
Reset
condition
State
on reset
External reset 00u0 0000
RR bit set
00u0 0000
RX0 — Receive pin 0 (passive) (Refer to Figure A-6)
1 (set)
–
VDD/2 will be connected to the input comparator. The RX0 pin is
disconnected.
0 (clear) –
The RX0 pin will be connected to the input comparator. VDD/2 is
disconnected.
RX1 — Receive pin 1 (passive) (Refer to Figure A-6)
1 (set)
Note:
–
VDD/2 will be connected to the input comparator. The RX1 pin is
disconnected.
0 (clear) –
The RX1 pin will be connected to the input comparator. VDD/2 is
disconnected.
A
If both RX0 and RX1 are set, or both are clear, then neither of the RX pins will be
disconnected.
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-9
116
Freescale Semiconductor, Inc.
COMPSEL — Comparator selector
1 (set)
–
0 (clear) –
RX0 and RX1 will be compared with VDD/2 during sleep mode (see
Figure A-6).
RX0 will be compared with RX1 during sleep mode.
SLEEP — Go to sleep
Freescale Semiconductor, Inc...
1 (set)
Note:
–
Sleep – The MCAN will go into sleep mode, as long as there are no
interrupts pending and there is no activity on the bus. Otherwise the
MCAN will issue a wake-up interrupt.
0 (clear) –
Wake-up – The MCAN will function normally. If SLEEP is cleared by
the CPU then the MCAN will waken up, but will not issue a wake-up
interrupt.
If SLEEP is set during the reception or transmission of a message, the MCAN will
generate an immediate wake-up interrupt. (This allows for a more orthogonal software
implementation on the CPU.) This will have no effect on the transfer layer, i.e. no
message will be lost or corrupted.
The CAF flag in the EEPROM control register (or Port Configuration register for
HC(7)05X4), indicates whether or not sleep mode was entered successfully.
A node that was sleeping and has been awakened by bus activity will not be able to
receive any messages until its oscillator has started and it has found a valid end of
frame sequence (11 recessive bits). The designer must take this into consideration
when planning to use the sleep command.
COS — Clear overrun status
1 (set)
–
0 (clear) –
This clears the read-only data overrun status bit in the CSTAT register
(see Section A.2.6). It may be written at the same time as RRB.
No action.
RRB — Release receive buffer
A
When set this releases the receive buffer currently attached to the CPU, allowing the buffer to be
reused by the MCAN. This may result in another message being received, which could cause
another receive interrupt request (if RIE is set). This bit is cleared automatically when a message
is received, i.e. when the RS bit (see Section A.2.6) becomes set.
1 (set)
–
0 (clear) –
Released – receive buffer is available to the MCAN.
No action.
TPG
MOTOROLA
A-10
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
117
Freescale Semiconductor, Inc.
AT — Abort transmission
When this bit is set a pending transmission will be cancelled if it is not already in progress, allowing
the transmit buffer to be loaded with a new (higher priority) message when the buffer is released.
If the CPU tries to write to the buffer when it is locked, the information will be lost without being
signalled. The status register can be checked to see if transmission was aborted or is still in
progress.
Freescale Semiconductor, Inc...
1 (set)
–
0 (clear) –
Present – Abort transmission of any pending messages.
No action.
TR — Transmission request
1 (set)
–
0 (clear) –
A.2.6
Present – Depending on the transmission buffer’s content, a data
frame or a remote frame will be transmitted.
No action. This will not cancel a previously requested transmission;
the abort transmission command must be used to do this.
MCAN status register (CSTAT)
This is a read only register; only the MCAN can change its contents.
MCAN status
(CSTAT)
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
$0022
BS
ES
TS
RS
TCS
TBA
DO
RBS
Reset condition
State
on reset
External reset 0000 1100
RR bit set
uu00 1100
BS — Bus status
This bit is set (off-bus) by the MCAN when the transmit error counter reaches 256. The MCAN will
then set RR and will remain off-bus until the CPU clears RR again. At this point the MCAN will wait
for 128 successive occurrences of a sequence of 11 recessive bits before clearing BS and
resetting the read and write error counters. While off-bus the MCAN does not take part in bus
activities.
1 (set)
–
0 (clear) –
Off-bus – The MCAN is not participating in bus activities.
On-bus – The MCAN is operating normally.
A
ES — Error status
1 (set)
–
0 (clear) –
Error – Either the read or the write error counter has reached the
CPU warning limit of 96.
Neither of the error counters has reached 96.
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-11
118
Freescale Semiconductor, Inc.
TS — Transmit status
1 (set)
–
0 (clear) –
Transmit – The MCAN has started to transmit a message.
Idle – If the receive status bit is also clear then the MCAN is idle;
otherwise it is in receive mode.
RS — Receive status
Freescale Semiconductor, Inc...
1 (set)
A
–
0 (clear) –
Receive – The MCAN entered receive mode from idle, or by losing
arbitration during transmission.
Idle – If the transmit status bit is also clear then the MCAN is idle;
otherwise it is in transmit mode.
TCS — Transmission complete status
This bit is cleared by the MCAN when TR becomes set. When TCS is set it indicates that the last
requested transmission was successfully completed. If, after TCS is cleared, but before
transmission begins, an abort transmission command is issued then the transmit buffer will be
released and TCS will remain clear. TCS will then only be set after a further transmission is both
requested and successfully completed.
1 (set)
–
0 (clear) –
Complete – Last requested transmission successfully completed.
Incomplete – Last requested transmission not complete.
TBA — Transmit buffer access
When clear, the transmit buffer is locked and cannot be accessed by the CPU. This indicates that
either a message is being transmitted, or is awaiting transmission. If the CPU writes to the transmit
buffer while it is locked, then the bytes will be lost without this being signalled.
1 (set)
–
0 (clear) –
Released – The transmit buffer may be written to by the CPU.
Locked – The CPU cannot access the transmit buffer.
DO — Data overrun
This bit is set when both receive buffers are full and there is a further message to be stored. In this
case the new message is dropped, but the internal logic maintains the correct protocol. The MCAN
does not receive the message, but no warning is sent to the transmitting node. The MCAN clears
DO when the CPU sets the COS bit in the CCOM register.
Note that data overrun can also be caused by a transmission, since the MCAN will temporarily
store an outgoing frame in a receive buffer in case arbitration is lost during transmission.
1 (set)
–
0 (clear) –
Overrun – Both receive buffers were full and there was another
message to be stored.
Normal operation.
TPG
MOTOROLA
A-12
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
119
Freescale Semiconductor, Inc.
RBS — Receive buffer status
This bit is set by the MCAN when a new message is available. When clear this indicates that no
message has become available since the last RRB command. The bit is cleared when RRB is set.
However, if the second receive buffer already contains a message, then control of that buffer is
given to the CPU and RBS is immediately set again. The first receive buffer is then available for
the next incoming message from the MCAN.
Freescale Semiconductor, Inc...
1 (set)
–
0 (clear) –
A.2.7
Full – A new message is available for the CPU to read.
Empty – No new message is available.
MCAN interrupt register (CINT)
All bits of this register are read only; all are cleared by a read of the register.
This register must be read in the interrupt handling routine in order to enable further interrupts.
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
WIF
OIF
EIF
TIF
RIF
Reset condition
State
on reset
External reset - - - 0 0000
MCAN interrupt (CINT) $0023
RR bit set
- - - u 0u00
WIF — Wake-up interrupt flag
If the MCAN detects bus activity whilst it is asleep, it clears the SLEEP bit in the CCOM register;
the WIF bit will then be set. WIF is cleared by reading the MCAN interrupt register (CINT), or by
an external reset.
1 (set)
–
0 (clear) –
MCAN has detected activity on the bus and requested wake-up.
No wake-up interrupt has occurred.
OIF — Overrun interrupt flag
When OIE is set then this bit will be set when a data overrun condition is detected. Like all the bits
in this register, OIF is cleared by reading the register, or when reset request is set.
1 (set)
–
0 (clear) –
A data overrun has been detected.
No data overrun has occurred.
A
EIF — Error interrupt flag
When EIE is set then this bit will be set by a change in the error or bus status bits in the MCAN
status register. Like all the bits in this register, EIF is cleared by reading the register, or by an
external reset.
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-13
120
Freescale Semiconductor, Inc.
1 (set)
–
0 (clear) –
There has been a change in the error or bus status bits in CSTAT.
No error interrupt has occurred.
TIF — Transmit interrupt flag
The TIF bit is set at the end of a transmission whenever both the TBA and TIE bits are set. Like all
the bits in this register, TIF is cleared by reading the register, or when reset request is set.
Freescale Semiconductor, Inc...
1 (set)
–
0 (clear) –
Transmission complete, the transmit buffer is accessible.
No transmit interrupt has occurred.
RIF — Receive interrupt flag
The RIF bit is set by the MCAN when a new message is available in the receive buffer, and the RIE
bit in CCNTRL is set. At the same time RBS is set. Like all the bits in this register, RIF is cleared
by reading the register, or when reset request is set.
1 (set)
–
0 (clear) –
A.2.8
A new message is available in the receive buffer.
No receive interrupt has occurred.
MCAN acceptance code register (CACC)
On reception each message is written into the current receive buffer. The MCU is only signalled to
read the message however, if it passes the criteria in the acceptance code and acceptance mask
registers (accepted); otherwise, the message will be overwritten by the next message (dropped).
Note:
This register can only be accessed when the reset request bit in the CCNTRL register
is set.
MCAN acceptance code (CACC)
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$0024
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
UndeÞned
AC7 – AC0 — Acceptance code bits
A
AC7 – AC0 comprise a user defined sequence of bits with which the 8 most significant bits of the
data identifier (ID10 – ID3) are compared. The result of this comparison is then masked with the
acceptance mask register. Once a message has passed the acceptance criterion the respective
identifier, data length code and data are sequentially stored in a receive buffer, providing there is
one free. If there is no free buffer, the data overrun condition will be signalled.
On acceptance the receive buffer status bit is set to full and the receive interrupt bit is set (provided
RIE = enabled).
TPG
MOTOROLA
A-14
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
121
Freescale Semiconductor, Inc.
A.2.9
MCAN acceptance mask register (CACM)
The acceptance mask register specifies which of the corresponding bits in the acceptance code
register are relevant for acceptance filtering.
Freescale Semiconductor, Inc...
Note:
This register can only be accessed when the reset request bit in the CCNTRL register
is set.
MCAN acceptance mask (CACM)
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$0025
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
UndeÞned
AM0 – AM7 — Acceptance mask bits
When a particular bit in this register is clear this indicates that the corresponding bit in the
acceptance code register must be the same as its identifier bit, before a match will be detected.
The message will be accepted if all such bits match. When a bit is set, it indicates that the state of
the corresponding bit in the acceptance code register will not affect whether or not the message
is accepted.
1 (set)
–
0 (clear) –
A.2.10
Note:
Ignore corresponding acceptance code register bit.
Match corresponding acceptance code register and identifier bits.
MCAN bus timing register 0 (CBT0)
This register can only be accessed when the reset request bit in the CCNTRL register
is set.
MCAN bus timing 0 (CBT0)
State
on reset
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
$0026
SJW1
SJW0
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0 UndeÞned
SJW1, SJW0 — Synchronization jump width bits
The synchronization jump width defines the maximum number of system clock (tSCL) cycles by
which a bit may be shortened, or lengthened, to achieve resynchronization on data transitions on
the bus (see Table A-2).
A
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-15
122
Freescale Semiconductor, Inc.
Table A-2 Synchronization jump width
Freescale Semiconductor, Inc...
SJW1
0
0
1
1
SJW0
0
1
0
1
Synchronization jump width
1 tSCL cycle
2 tSCL cycles
3 tSCL cycles
4 tSCL cycles
BRP5 – BRP0 — Baud rate prescaler bits
These bits determine the MCAN system clock cycle time (tSCL), which is used to build up the
individual bit timing, according to Table A-3 and the formula in Figure A-4.
Table A-3 Baud rate prescaler
BRP5
0
0
0
0
:
:
1
fosc
OSC1
BRP4
0
0
0
0
:
:
1
BRP3
0
0
0
0
:
:
1
Divide by
2
BRP2
0
0
0
0
:
:
1
BRP1
0
0
1
1
:
:
1
BRP0
0
1
0
1
:
:
1
Prescaler value (P)
1
2
3
4
:
:
64
fosc/2
Prescaler (P)
tSCL =
2P
fosc
MCAN module system clock
Divide by
10, 8, 4, or 2
fOP
MCU bus clock
A
Figure A-4 Oscillator block diagram
TPG
MOTOROLA
A-16
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
123
Freescale Semiconductor, Inc.
A.2.11
MCAN bus timing register 1 (CBT1)
This register can only be accessed when the reset request bit in the CCNTRL register is set.
Address
Freescale Semiconductor, Inc...
MCAN bus timing 1 (CBT1)
$0027
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
SAMP TSEG22TSEG21TSEG20TSEG13TSEG12TSEG11TSEG10 UndeÞned
SAMP — Sampling
This bit determines the number of samples of the serial bus to be taken per bit time. When set three
samples per bit are taken. This sample rate gives better rejection of noise on the bus, but
introduces a one bit delay to the bus sampling. For higher bit rates SAMP should be cleared, which
means that only one sample will be taken per bit.
1 (set)
–
0 (clear) –
Three samples per bit.
One sample per bit.
TSEG22 – TSEG10 — Time segment bits
Time segments within the bit time fix the number of clock cycles per bit time, and the location of
the sample point.
BIT_TIME
TSEG 1
SYNC_SEG
1 clock cycle
tSCL
Transmit point
TSEG 2
Sample point
SYNC_SEG
Transmit point
Figure A-5 Segments within the bit time
SYNC_SEG
System expects transitions to occur on the bus during this period.
Transmit point
A node in transmit mode will transfer a new value to the MCAN bus at this point.
Sample point
A node in receive mode will sample the bus at this point. If the three samples per
bit option is selected then this point marks the position of the third sample.
A
Time segment 1 (TSEG1) and time segment 2 (TSEG2) are programmable as shown in Table A-4.
The bit time is determined by the oscillator frequency, the baud rate prescaler, and the number of
bus clock cycles (tSCL) per bit (as shown above).
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-17
124
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Table A-4 Time segment values
TSEG13
0
0
0
.
.
1
TSEG12 TSEG11 TSEG10
0
0
1
0
1
0
0
1
1
.
.
.
.
.
.
1
1
1
Time segment 1
2 tSCL cycles
3 tSCL cycles
4 tSCL cycles
.
.
16 tSCL cycles
TSEG22 TSEG21 TSEG20
0
0
1
.
.
.
.
.
.
1
1
1
Time segment 2
2 tSCL cycles
.
.
8 tSCL cycles
Calculation of the bit time
BIT_TIME = SYNC_SEG + TSEG1 + TSEG2
Note:
TSEG2 must be at least 2 tSCL, i.e. the configuration bits must not be 000. (If three
samples per bit mode is selected then TSEG2 must be at least 3 tSCL.)
TSEG1 must be at least as long as TSEG2.
The synchronization jump width (SJW) may not exceed TSEG2, and must be at least
tSCL shorter than TSEG1 to allow for physical propagation delays.
i.e. in terms of tSCL:
SYNC_SEG = 1
TSEG1 ≥ SJW + 1
TSEG1 ≥ TSEG2
TSEG2 ≥ SJW
and
TSEG2 ≥ 2
(SAMP = 0)
or
TSEG2 ≥ 3
(SAMP = 1)
These boundary conditions result in minimum bit times of 5 tSCL, for one sample, and 7 tSCL, for
three samples per bit.
A
TPG
MOTOROLA
A-18
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
125
Freescale Semiconductor, Inc.
A.2.12
MCAN output control register (COCNTRL)
This register allows the setup of different output driver configurations under software control. The
user may select active pull-up, pull-down, float or push-pull output.
Freescale Semiconductor, Inc...
Note:
This register can only be accessed when the reset request bit in the CCNTRL register
is set.
Address
MCAN output control (COCNTRL)
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$0028 OCTP1 OCTN1 OCPOL1 OCTP0 OCTN0 OCPOL0 OCM1 OCM0 UndeÞned
OCM1 and OCM0 — Output control mode bits
The values of these two bits determine the output mode, as shown in Table A-5.
Table A-5 Output control modes
Note:
OCM1
0
0
OCM0
0
1
1
0
1
1
Function
Biphase mode
Not used
Normal mode 1
Bit stream transmitted on both TX0 and TX1
Normal mode 2
TX0 - bit sequence
TX1 - bus clock (txclk)
The transmit clock (txclk) is used to indicate the end of the bit time and will be high during
the SYNC_SEG.
For all the following modes of operation, a dominant bit is internally coded as a zero, a
recessive as a one. The other output control bits are used to determine the actual
voltage levels transmitted to the MCAN bus for dominant and recessive bits.
A
Biphase mode
If the CAN modules are isolated from the bus lines by a transformer then the bit stream has to be
coded so that there is no resulting dc component. There is a flip-flop within the MCAN that keeps
the last dominant configuration; its direct output goes to TX0 and its complement to TX1. The
flip-flop is toggled for each dominant bit; dominant bits are thus sent alternately on TX0 and TX1;
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-19
126
Freescale Semiconductor, Inc.
i.e. the first dominant bit is sent on TX0, the second on TX1, the third on TX0 and so on. During
recessive bits, all output drivers are deactivated (i.e. high impedance).
Normal mode 1
In contrast to biphase mode the bit representation is time invariant and not toggled.
Freescale Semiconductor, Inc...
Normal mode 2
For the TX0 pin this is the same as normal mode 1, however the data stream to TX1 is replaced
by the transmit clock. The rising edge of the transmit clock marks the beginning of a bit time. The
clock pulse will be tSCL long.
Other output control bits
The other six bits in this register control the output driver configurations, to determine the format
of the output signal for a given data value (see Figure A-6).
OCTP0/1 – These two bits control whether the P-type output control transistors are enabled.
OCTN0/1 – These two bits control whether the N-type output control transistors are enabled.
OCPOL0/1 – These two bits determine the driver output polarity for each of the MCAN bus lines
(TX0, TX1).
TP0/1 and TN0/1 – These are the resulting states of the output transistors.
TD – This is the internal value of the data bit to be transferred across the MCAN bus. (A zero
corresponds to a dominant bit, a one to a recessive.)
The actions of these bits in the output control register are as shown in Table A-6.
A
TPG
MOTOROLA
A-20
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
127
Freescale Semiconductor, Inc.
Table A-6 MCAN driver output levels
Mode
Freescale Semiconductor, Inc...
Float
Pull-down
Pull-up
Push-pull
A.2.13
TD
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
OCPOLi
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
OCTPi
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
OCTNi
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
TPi
Off
Off
Off
Off
Off
Off
Off
Off
Off
On
On
Off
Off
On
On
Off
TNi
Off
Off
Off
Off
On
Off
Off
On
Off
Off
Off
Off
On
Off
Off
On
TXi output level
Float
Float
Float
Float
Low
Float
Float
Low
Float
High
High
Float
Low
High
High
Low
Transmit buffer identifier register (TBI)
Transmit buffer identiÞer (TBI)
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$002A
ID10
ID9
ID8
ID7
ID6
ID5
ID4
ID3
UndeÞned
ID10 – ID3 — Identifier bits
The identifier consists of 11 bits (ID10 – ID0). ID10 is the most significant bit and is transmitted first
on the bus during the arbitration procedure. The priority of an identifier is defined to be highest for
the smallest binary number. The three least significant bits are contained in the TRTDL register.
The seven most significant bits must not all be recessive.
A
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-21
128
Freescale Semiconductor, Inc.
A.2.14
Remote transmission request and data length code
register (TRTDL)
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
$002B
ID2
ID1
ID0
RTR
DLC3
DLC2
DLC1
DLC0 UndeÞned
RTR and data length code (TRTDL)
Freescale Semiconductor, Inc...
State
on reset
Address
ID2 – ID0 — Identifier bits
These bits contain the least significant bits of the transmit buffer identifier.
RTR — Remote transmission request
1 (set)
–
0 (clear) –
A remote frame will be transmitted.
A data frame will be transmitted.
DLC3 – DLC0 — Data length code bits.
The data length code contains the number of bytes (data byte count) of the respective message.
At transmission of a remote frame, the data length code is ignored, forcing the number of bytes to
be 0. The data byte count ranges from 0 to 8 for a data frame. Table A-7 shows the effect of setting
the DLC bits.
Table A-7 Data length codes
DLC3
0
0
0
0
0
0
0
0
1
A
Data length code
DLC2
DLC1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
0
0
DLC0
0
1
0
1
0
1
0
1
0
Data byte
count
0
1
2
3
4
5
6
7
8
TPG
MOTOROLA
A-22
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
129
Freescale Semiconductor, Inc.
A.2.15
Transmit data segment registers (TDS) 1 – 8
Transmit data segment (TDS)
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$002C Ð
$0033
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
UndeÞned
Freescale Semiconductor, Inc...
DB7 – DB0 — data bits
These data bits in the eight data segment registers make up the bytes of data to be transmitted.
The number of bytes to be transmitted is determined by the data length code.
A.2.16
Receive buffer identifier register (RBI)
The layout of this register is identical to the TBI register (see Section A.2.13).
Receive buffer identiÞer (RBI)
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$0034
ID10
ID9
ID8
ID7
ID6
ID5
ID4
ID3
UndeÞned
(Note that there are actually two receive buffer register sets, but switching between them is
handled internally by the MCAN.)
A.2.17
Remote transmission request and data length code
register (RRTDL)
The layout of this register is identical to the TRTDL register (see Section A.2.14).
RTR and data length code (RRTDL)
A.2.18
State
on reset
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
$0035
ID2
ID1
ID0
RTR
DLC3
DLC2
DLC1
DLC0 UndeÞned
Receive data segment registers (RDS) 1 – 8
A
The layout of these registers is identical to the TDSx registers (see Section A.2.15).
Receive data segment (RDS)
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$0036 Ð
$003D
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
UndeÞned
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-23
130
Freescale Semiconductor, Inc.
(Note that there are actually two receive buffer register sets, but switching between them is
handled internally by the MCAN.)
Termination
network
1.75V 3.25V
TXP0
2 kΩ 2 kΩ
TX0
Freescale Semiconductor, Inc...
680Ω
TXN0
TXP1
TX1
680Ω
TXN1
RX0 passive
150kΩ
RX0
RX1 passive
150kΩ
RX1
+
SC
Ð
2 x 30kΩ
+
SC
Ð
CANH
MCAN bus lines
COMPSEL
&
Wake-up
+
SC
Ð
CANL
A
Data
+
AC
Ð
VDDH
VDD/2
Internal to the CAN PROTOCOL MCAN module
Figure A-6 A typical physical interface between the MCAN and the MCAN bus
lines
TPG
MOTOROLA
A-24
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
131
Freescale Semiconductor, Inc.
A.2.19
Organization of buffers
Further details on these registers will be found in the appropriate device data sheet.
Freescale Semiconductor, Inc...
Table 1-8 MCAN data buffers
Register
Transmit Buffer Identity (TBI)
RTRbit, Data length code (TRTDL)
Transmit Data segment 1 (TDS1)
Transmit Data segment 2 (TDS2)
Transmit Data segment 3 (TDS3)
Transmit Data segment 4 (TDS4)
Transmit Data segment 5 (TDS5)
Transmit Data segment 6 (TDS6)
Transmit Data segment 7 (TDS7)
Transmit Data segment 8 (TDS8)
Receive Buffer Identity (RBI)
RTRbit, Data length code (RRTDL)
Receive Data segment 1 (RDS1)
Receive Data segment 2 (RDS2)
Receive Data segment 3 (RDS3)
Receive Data segment 4 (RDS4)
Receive Data segment 5 (RDS5)
Receive Data segment 6 (RDS6)
Receive Data segment 7 (RDS7)
Receive Data segment 8 (RDS8)
Address bit 7
$002A
ID10
$002B
ID2
$002C
DB7
$002D
DB7
$002E
DB7
$002F
DB7
$00030
DB7
$00031
DB7
$00032
DB7
$00033
DB7
$00034
ID10
$00035
ID10
$00036
DB7
$00037
DB7
$00038
DB7
$00039
DB7
$0003A
DB7
$0003B
DB7
$0003C
DB7
$0003D
DB7
bit 6
ID9
ID1
DB6
DB6
DB6
DB6
DB6
DB6
DB6
DB6
ID9
ID9
DB6
DB6
DB6
DB6
DB6
DB6
DB6
DB6
bit 5
ID8
ID0
DB5
DB5
DB5
DB5
DB5
DB5
DB5
DB5
ID8
ID8
DB5
DB5
DB5
DB5
DB5
DB5
DB5
DB5
bit 4
ID7
RTR
DB4
DB4
DB4
DB4
DB4
DB4
DB4
DB4
ID7
ID7
DB4
DB4
DB4
DB4
DB4
DB4
DB4
DB4
bit 3
ID6
DLC3
DB3
DB3
DB3
DB3
DB3
DB3
DB3
DB3
ID6
ID6
DB3
DB3
DB3
DB3
DB3
DB3
DB3
DB3
bit 2
ID5
DLC2
DB2
DB2
DB2
DB2
DB2
DB2
DB2
DB2
ID5
ID5
DB2
DB2
DB2
DB2
DB2
DB2
DB2
DB2
bit 1
ID4
DLC1
DB1
DB1
DB1
DB1
DB1
DB1
DB1
DB1
ID4
ID4
DB1
DB1
DB1
DB1
DB1
DB1
DB1
DB1
bit 0
ID3
DCL0
DB0
DB0
DB0
DB0
DB0
DB0
DB0
DB0
ID3
ID3
DB0
DB0
DB0
DB0
DB0
DB0
DB0
DB0
A
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
A-25
132
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
THIS PAGE LEFT BLANK INTENTIONALLY
A
TPG
MOTOROLA
A-26
THE MOTOROLA CAN (MCAN) MODULE
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
133
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
B
TOUCAN
B.1
Introduction
The TOUCAN Module is designed in a modular structure for use in Motorola’s Modular
Microcontroller Family (MMF) or for the RISC family. The TOUCAN module is a communication
controller implementing the CAN protocol. A general working knowledge of the IMB3 signals and
bus control is assumed in the writing of this document.
The TOUCAN supports 2 methods of Interrupt architechture (MODULAR and RISC), which can be
chosen by a mask programming option (IRQ_PLUG).
The TOUCAN supports 2 methods of berr architechture (MODULAR and RISC), which can be
chosen by a mask programming option (BERR_PLUG).
The CAN protocol was primarily, but not exclusively, designed to be used as a vehicle serial data
bus, meeting the specific requirements of this field, i.e. real-time processing, cost-effectiveness,
required bandwidth and reliable operation in the EMI environment of a vehicle.
B.2
TOUCAN module features
•
Motorola IMB3-Family Modular Architecture
•
Full implementation of the CAN Protocol Specification, Version 2.0
–
Standard data and remote frames (up to 109 bits long)
–
Extended data and remote frames (up to 127 bits long)
–
0-8 bytes data length
–
Programmable bit rate up to 1Mbit/sec
B
•
16 message buffers (MBs) of 0-8 bytes data length; each of these can be configured as Rx or
Tx and can support standard and extended messages
•
Content-related addressing
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-1
134
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
•
No read/write semaphores
•
Three programmable mask registers: Global (for MBs 0-13), Special for MB14 and Special for
MB15
•
Programmable ‘transmit-first’ scheme based on lowest ID or lowest buffer number
•
Time stamp, based on 16-bit free-running timer
•
Global network time, synchronized by a specific message
•
Programmable I/O modes
•
Maskable interrupts
•
Independent of transmission medium (external transceiver is assumed)
•
Open network architecture
•
Multimaster concept
•
High immunity to EMI
•
Short latency time for high-priority messages
•
Low power sleep mode, with programmable wake-up on bus activity
A block diagram describing the various sub-modules of the TOUCAN module is shown in
Figure B-1. Each sub-module is described in detail in subsequent sections.
Tx0
16 Rx/Tx
Message
Buffers
(MBs)
Transmitter
Tx1
Control
Receiver
Rx0
Slave Bus Interface Unit
B
Inter-Module Bus (IMB3)
Figure B-1 TOUCAN block diagram and pinout
MOTOROLA
B-2
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
135
Freescale Semiconductor, Inc.
B.3
External Pins
Freescale Semiconductor, Inc...
The TOUCAN module interface to the CAN bus is composed of 3pins: Tx0 and Tx1, which are the
serial transmitted data, and Rx0, which are the serial received data. Dominant state is defined as
Tx0=0 and Tx1=1. The opposite state is defined as recessive state. The same applies respectively
to the Rx0 pin.
The minimum set of pins that may be bonded out in a chip is the Tx0 and Rx0 pins only. Such a
configuration is based on the use of an external transceiver to interface to the CAN bus.
B.4
The CAN system
A typical CAN system is shown in Figure B-2.
CAN station 1
CAN station 2
.....
CAN station n
CAN system
TOUCAN
Tx0
Rx0
Transceiver
B
CAN
Figure B-2 Typical CAN system
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-3
136
Freescale Semiconductor, Inc.
Each CAN station is physically connected to the CAN bus through a transceiver. The transceiver
is capable of driving the large current needed for the CAN bus and has current protection against
a defective CAN bus or defective stations.
Freescale Semiconductor, Inc...
B.5
Message buffer structure
Figure B-3 describes the message buffer structure.
15
Extended Identifier
8 7
TIME STAMP
$0
4 3
CODE
LENGTH
SRR IDE
ID[28-18]
$2
0
ID[17-15]
RTR
$4
$6
DATA BYTE 0
DATA BYTE 1
$8
DATA BYTE 2
DATA BYTE 3
$A
DATA BYTE 4
DATA BYTE 5
$C
DATA BYTE 6
DATA BYTE 7
RESERVED
$E
15
Standard Identifier
$2
$4
4 3
ID[28-18]
RTR
0
0
0
0
0
TIME STAMP
Figure B-3 Message buffer structure
B
MOTOROLA
B-4
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
137
Freescale Semiconductor, Inc.
B.6
Common fields to extended and standard format frames
B.6.1
CODE
Freescale Semiconductor, Inc...
The CODE bits are described for Rx buffers and Tx buffers in Table B-1 and Table B-2
respectively.
Table B-1 Message buffer code for Rx buffers
Rx code
before Rx
new frame
0000
0100
0010
0110
0XY1(1)
Description
Not active: MB is not active.
Empty: MB is active and empty.
Full: MB is full.
Overrun: Second frame was received
into a full buffer before the CPU read
the Þrst one.
Rx code
after Rx new
frame
Ñ
0010
0110
Busy: MB is now being Þlled with a new
receive frame. This condition will be
cleared within 20 cycles.
0110
0010
0110
Comment
If a CPU read occurs before the new
frame, new Rx code is 0010.
An empty buffer was Þlled (XY was
10).
A full/overrun buffer was Þlled (Y was
1).
(1) Note that for Tx MBs (see Table B-2) upon read, the BUSY bit should be ignored.
Table B-2 Message buffer code for Tx buffers
RTR
Initial Tx code
X
0
1000
1100
1
1100
0
1010(1)
0
1110
Code after
successful
Description
transmission
Ñ
MB not ready for transmission.
1000
Data frame to be transmitted once, unconditionally.
Remote frame to be transmitted once, and MB becomes
0100
a receive MB for data frames.
Data frame to be transmitted only as a response to
1010
remote frame.
Data frame to be transmitted once, unconditionally. It
1010
then becomes an MB of the previous type.
B
(1) Note that when a matching remote request frame is detected, the code for such an MB becomes
Ô1110Õ.
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-5
138
Freescale Semiconductor, Inc.
B.6.2
LENGTH (receive mode)
This is the length (in bytes) of the Rx data stored in offset $6-$D of this buffer. This field is written
by the TOUCAN module, copied from the Data Length Code (DLC) field of the received frame.
Freescale Semiconductor, Inc...
B.6.3
LENGTH (transmit mode)
This is the length (in bytes) of the data to be transmitted, located in offset $6-$D of this buffer. This
field is written by the CPU and is also the DLC field value. Note that if RTR=1, the frame is a remote
frame and will be transmitted without data field, regardless of the length field.
B.6.4
DATA BYTE 0..7
Up to eight data bytes can be stored for a frame. For Rx frames, the data is stored as it is received
from the line; for Tx frames the CPU prepares the data field to be transmitted within the frame.
B.6.5
RESERVED
This word entry (16 bits) should not be accessed by the CPU.
B
MOTOROLA
B-6
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
139
Freescale Semiconductor, Inc.
B.7
Fields for extended format frames
B.7.1
TIME STAMP
Freescale Semiconductor, Inc...
This is a copy of the high byte of the free-running timer, which was captured at the beginning of
the identifier field of this buffer’s frame on the CAN bus.
B.7.2
ID[28-18, 17-15]
These are the 14 MSBs of the extended identifier, located in the ID_HIGH word of the message
buffer.
B.7.3
SRR — Substitute remote request
Fixed recessive bit, used only in extended format. Should be set to ‘1’ by the user for Tx buffers,
and will be stored as received on the CAN bus, for Rx buffers.
B.7.4
IDE — ID Extended
This field should be set to ‘1’ if extended format frame should be used. If this bit is set to ‘0’, refer
to Section B.8.
B.7.5
ID[14-0]
Bits 14-0 of the Extended Identifier, located in the ID_LOW word of the message buffer.
B.7.6
RTR — Remote transmission request
B
This bit is the least significant bit of the ID_LOW word of the message buffer.
1 (set)
–
0 (clear) –
CAN PROTOCOL
Rev. 3
This is a remote frame.
This is a data frame.
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-7
140
Freescale Semiconductor, Inc.
B.8
Fields for standard format frames
B.8.1
TIME STAMP
Freescale Semiconductor, Inc...
The ID_LOW word, which is not required for standard format, is used in standard format buffer to
store the value of the free-running timer captured at the beginning of the Identifier field of this
buffer’s frame on the CAN bus.
B
B.8.2
ID[28-18]
Bits 28-18 of the Identifier, located in the ID_HIGH word of the message buffer. Note that the four
least significant bits in the Standard Identifier (bits 3-0 in ID_HIGH word) must be set to 0000 to
ensure proper operation of TOUCAN.
B.8.3
RTR — Remote transmission request
This bit is located in the ID_HIGH word of the message buffer. Its operation is as follows.
1 (set)
–
0 (clear) –
B.8.4
This is a remote frame
This is a data frame
RTR/SRR bit treatment
If TOUCAN transmits this bit as ‘1’ and receives it as ‘0’, then it interprets it as arbitration loss; if
this bit is transmitted as ‘0’, then received as a ‘1’, TOUCAN treats it as a bit error; if the value
received matches the value transmitted, it is considered to be a successful bit transmission.
B.9
Functional overview
The TOUCAN module is flexible in that each one of its 16 message buffers can be assigned either
as a Tx buffer or an Rx buffer. Each message buffer is also assigned an interrupt flag bit, to indicate
successful completion of transmission or receipt. Note that for both processes, the first CPU action
in preparing a message buffer should be to deactivate it by setting its code field to the proper value
(refer to Table B-1). This requirement is mandatory to ensure proper operation.
MOTOROLA
B-8
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
141
Freescale Semiconductor, Inc.
B.10
Transmit process
The CPU prepares/changes a message buffer for transmission by executing the following steps:
i)
Writing the control/status word to hold inactive Tx message buffer (code =
1000)
ii) Writing the ID_HIGH and ID_LOW words
Freescale Semiconductor, Inc...
iii) Writing the data bytes
iv) Writing the control/status word (active code, length)
Note:
The first and last steps are mandatory.
Starting with step iv), this message buffer will participate in the internal arbitration process, which
takes place every time the CAN bus is sensed as being free by the receiver or at the inter-frame
space, and there is at least one message buffer ready for transmission. This internal arbitration
process is intended to select the message buffer from which the next frame is transmitted.
When this process is over, and there is a winner message buffer for transmission, the frame is
transferred to the serial message buffer (SMB) for transmission (Move Out).
While transmitting, TOUCAN transmits up to eight data bytes, even if the DLC is bigger in value.
At the end of the successful transmission, the value of the free-running timer (which was captured
at the beginning of the identifier field on the CAN bus), is written into the TIME STAMP field in the
message buffer, the code field in the control/status word of the message buffer is updated and a
status flag is set in the IFLAGH/IFLAGL register.
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-9
142
Freescale Semiconductor, Inc.
B.11
Receive process
The CPU prepares/changes a new message buffer for frame receipt by executing the following
steps:
i)
Writing the control/status word to hold inactive Rx message buffer (code =
0000)
Freescale Semiconductor, Inc...
ii) Writing the ID-HIGH and ID_LOW words
B
iii) Writing the control/status word to mark a receive message buffer is active
and empty
Note:
The first and last steps are mandatory.
Starting with step iii), this message buffer is an active Rx buffer and will participate in the internal
matching process, which takes place every time the receiver receives an error-free frame. In this
process, all active Rx buffers compare their ID value to the newly received one. If a match occurs,
the frame is transferred (move in) to the first (i.e. lowest entry) matching message buffer, i.e. the
value of the free-running timer (which was captured at the beginning of the identifier field on the
CAN bus) is written into the TIME STAMP field in the message buffer, the ID, data field (8 bytes
maximum) and the LENGTH field are stored, the code field is updated and a status flag is set in
the IFLAGH/IFLAGL register.
The CPU should read an Rx frame from its message buffer as follows:
–
Control/status word (mandatory-activates internal lock for this buffer)
–
ID (optional-only required if a mask was used)
–
Data field word(s)
–
Free-running timer (releases internal lock)
The read of the free-running timer is not mandatory. If not executed, the message buffer remains
locked unless the CPU starts the read process for another message buffer. Note that only a single
message buffer is locked at any one time. The only mandatory CPU read operation is of the
control/status word, to ensure data coherency; if, however, the BUSY bit is set in the message
buffer code, then the CPU should defer until this bit is negated. Refer to Table B-1.
The CPU should synchronize to frame receipt by the status flag for the specific message buffer
(see Section B.25.3.), and not by the Control/Status word code field for that message buffer; this
is because polling after the Control/Status word may lock the message buffer (see above), and the
code may change before the full frame is received into the message buffer.
Note:
The received Identifier field is always stored in the matching message buffer, thus the
contents of the Identifier Field in an message buffer may change if the match was due
to a mask.
MOTOROLA
B-10
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
143
Freescale Semiconductor, Inc.
B.11.1
Self-received frames
TOUCAN receives self transmitted frames if an Rx matching message buffer exists.
Freescale Semiconductor, Inc...
B.12
Message buffer handling
In order to maintain data coherency and proper TOUCAN operation, the CPU must obey the rules
listed in Section B.10 and Section B.11. Deactivation of a message buffer is a host action that
causes that message buffer to be excluded from TOUCAN transmit or receive processes; any CPU
write access to a Control/Status word of message buffer structure deactivates that message buffer,
thus excluding it from Rx/Tx processes. Also, any form of CPU access to a message buffer
structure (other than those listed in Section B.10 and Section B.11) may cause TOUCAN to
behave in an unpredictable way.
The Match/Arbitration processes are conducted only once by TOUCAN. Once a winner/match is
determined, no re-evaluation is conducted whatsoever, i.e. an Rx frame may be lost. If two or more
message buffers have an ID which matches that of a received frame, then receipt by TOUCAN is
not guaranteed if the matching message buffer has been deactivated after the second one has
been scanned.
B.12.1
Tx message buffer deactivation
There is a point in time before which deactivation of a Tx message buffer causes it not to be
transmitted (End of Move), and after which the message buffer is transmitted, but no interrupt is
issued and the code is not updated. If a message buffer containing the lowest ID is deactivated
after TOUCAN has scanned it while in the arbitration process, TOUCAN may transmit a message
buffer with an ID which may not be the lowest at the time.
B.12.2
Rx message buffer deactivation
If the deactivation occurs during move in, then it is stopped and no interrupt is issued, but the
message buffer contains mixed data from two different frames. In order to prevent the host from
writing data into an Rx message buffer data word(s) while it is being moved in, its Control/Status
word is changed to reflect FULL or OVRN, but no interrupt will be permitted-this is expressly
forbidden.
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
B
MOTOROLA
B-11
144
Freescale Semiconductor, Inc.
B.13
Lock/release/BUSY mechanism and SMB usage
This mechanism is implemented in order to assure data coherency in both the receive and transmit
processes. The mechanism includes lock status for a message buffer, and two SMBs to buffer
frame transfers within TOUCAN.
Freescale Semiconductor, Inc...
The following points should be noted:
B
•
A CPU read of a control/status word of a message buffer triggers a lock for that message buffer,
e.g. a new Rx frame which matches this message buffer, cannot be written into it
•
In order to release a locked message buffer, the CPU should either lock another message
buffer (by reading its control/status word), or globally release any locked message buffer (by
reading the free-running timer)
•
If an Rx frame with a matching ID is received while a message buffer is locked, then it cannot
be stored within that message buffer, and it remains in the SMB. No indication of this situation
is given
•
If two or more Rx frames with matching ID are received while an message buffer is locked, then
the last received frame is kept within the SMB, while all preceding ones are lost. No indication
of this situation is given
•
If a locked message buffer is released, and a matching frame exists within the SMB, this frame
is then transferred to the matching message buffer
•
If the CPU reads a Rx message buffer while it is receiving (from SMB), then the BUSY code
bit is set in the control/status word, and to ensure data coherency the CPU should wait until
this bit is negated before further reading from that message buffer. Note that such a message
buffer is not locked
•
If the CPU deactivates a locked message buffer, then its lock status is negated, but no data is
transferred into that message buffer
B.14
Remote frames
A remote frame is a special kind of frame: The user initializes a remote frame as a Transmit
message buffer with it’s RTR bit set to ‘1’. After the remote frame is transmitted successfully, it’s
message buffer becomes a receive message buffer, with the same ID as before. When the remote
frame is received by TOUCAN, its ID is compared to the IDs of the transmit message buffers with
a code of 1010. If there is a matching ID, then this message buffer’s frame will be transmitted.
Note:
If the matching identifier message buffer holds the RTR bit set, then TOUCAN will
transmit a remote frame as a response.
MOTOROLA
B-12
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
145
Freescale Semiconductor, Inc.
A received remote Request frame is not stored in a Rx buffer, but is only used to trigger a
transmission of a frame in response. The mask registers are not used in remote frame matching,
and all ID bits of the incoming received frame should match.
Freescale Semiconductor, Inc...
In the case that a remote Request frame is received which matches a message buffer, this
message buffer immediately enters the internal arbitration process, but is treated as a normal Tx
message buffer, with no higher priority. The frame’s data length is independent of the DLC field in
the remote frame that initiated its transmission.
For further information, refer to Table B-2.
B.15
Overload frames
TOUCAN does not initiate a transmission of an overload frame. It does however transmit overload
frames due to detection of the following conditions on the CAN bus:
•
Detection of a dominant bit in the first/second bit of INTERMISSION
•
Detection of a dominant bit at the 7th (last) bit of End_of_frame field (Rx frames)
•
Detection of a dominant bit at the 8th (last) bit of error frame’s delimiter or overload frame’s
delimiter
B.16
Time stamp
The value of the free running 16-bit timer, is sampled at the beginning of the identifier field on the
CAN bus, and is stored at the end-of-frame time in the TIME STAMP entry. Knowledge of network
behaviour with respect to time is therefore gained. This feature can help in network development
and diagnostics.
Note:
The free running timer can be reset upon a specific frame receipt, enabling network
time synchronisation. Refer to the TSYNC bit in CTRL1 register.
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-13
146
Freescale Semiconductor, Inc.
B.17
Bit-timing configuration
Freescale Semiconductor, Inc...
TOUCAN supports a variety of means to set up the bit-timing parameters that are required by the
CAN protocol. There are three 8-bit registers that enable the user to determine the value of various
fields of the bit timing parameters: PROPSEG, PSEG1, PSEG2 and the RJW are programmed
through fields in CTRL1 and CTRL2 registers. Also, TOUCAN contains a prescaler that enables
the ratio between the system clock (IMB3 ICLOCK) and the time quanta clock (SCLOCK) to be
determined. Refer to Table B-3.
B
Table B-3 Examples of system clock/CAN bit-rate/SCLOCK
System clock
CAN bit-rate
frequency
(MHz)
(MHz)
24
20
16
24
20
16
Note:
1
1
1
0.125
0.125
0.125
Possible
Sclock
frequency
(MHz)
8, 12, 24
10, 20
8, 16
1, 1.5, 2, 3
1, 2, 2.5
1, 2
Possible
number of
time-quanta/
bit
8, 12, 24
10, 20
8, 16
8, 12, 16, 24
8, 16, 20
8, 16
Prescaler
programmed
value + 1
Comments
3, 2, 1
2, 1
Min. 8 time-quanta
2, 1
24, 16, 12, 8
Max. 25 time-quanta
20, 10, 8
16, 8
Bit Time = 1 + (PROPSEG + 1) + (PSEG1 + 1) + (PSEG2 + 1) x time quanta
B.18
Bit-timing operation notes
•
In cases where the programmed value indicates single system clock per time quantum, then
the PSEG2 field in CTRL2 should not be programmed to be less than 1
•
In cases where the programmed value indicates single system clock per time quantum, the
Information Processing Time IPT = 3, otherwise IPT = 2. Note that if PSEG2 = 2, then TOUCAN
transmits 1 time quantum late relative to the scheduled sync segment
•
In cases where the programmed values in the prescaler and the bit-timing control fields
indicate that the number of system clocks per one bit time is less than 10 clocks, then for 100%
loaded CAN bus and if the start-of-frame always comes in the 3rd bit of transmission, the
TOUCAN may not complete preparing a message buffer for transmission on time, hence the
TOUCAN may not go out for transmission
•
At least nine system clocks per bit must be programmed in TOUCAN, otherwise correct
operation is not guaranteed
MOTOROLA
B-14
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
147
Freescale Semiconductor, Inc.
B.19
TOUCAN initialisation sequence
Freescale Semiconductor, Inc...
TOUCAN may be reset in two ways: a hard reset using one of the IMB3 reset lines, or by asserting
SFTRST in MCR. Following the negation of the reset, TOUCAN is out of synchronization with the
CAN bus, the HALT and FRZ1 bits in MCR are set, the main control is disabled and the FRZAK
and NTRDY bits in MCR are set. The TOUCAN Tx pins are in recessive state and no frames are
transmitted or received. The message buffer’s contents are not changed following reset.
For any configuration change/initialization, TOUCAN should either be frozen (by asserting the
HALT bit in MCR), or reset (refer to Section B.20).
The following is a generic initialisation sequence applicable to TOUCAN:
i) Initialise all operation modes
–
Tx and Rx pin modes (CTRL0 register)
–
Bit timing parameters: PROPSEG, PSEG1, PSEG2, RJW (CTRL1 & CTRL2
registers)
–
Determine the bit rate by programming the PRESDIV register
–
Determine internal arbitration mode (LBUF bit in CTRL1 register)
ii) Initialize message buffers
–
The control/status word of all message buffers must be written either as an
active or inactive message buffer
–
Other entries in each message buffer should be initialized as required
iii) Initialize MASK registers for acceptance mask as required
iv) Initialize TOUCAN’s interrupt handler
–
Initialize ICR register’s field (request level and vector value)
–
Initialise interrupt arbitration identifier to a non-zero value (if interrupts from
TOUCAN are desired) in MCR reegister
–
Set required MASK bits in IMASKH/IMASKL register (for all message buffers
interrupts), in CTRL0 register (for BOFF and error interrupts) and in MCR
register for wake interrupt
v) Negate the HALT bit in the MCR register
–
B
Starting with this event, TOUCAN attempts to synchronise with the CAN bus
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-15
\ 148
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
B
B.20
Special operating modes
B.20.1
DEBUG mode
This is a special debug mode which is entered by asserting the HALT bit in MCR, or by asserting
the IMB3 FREEZE line. Entering the DEBUG mode however, also depends on the state of the
FRZ1 bit in MCR; for further information refer to Section B.22.4. Once in DEBUG mode, TOUCAN
will wait until it is in either: intermission, passive error, BUSOFF, or IDLE state. After one of these
conditions is satisfied, TOUCAN will wait for all activity (other than that in the CAN bus interface)
to finish and then the following steps take place:
–
TOUCAN will stop transmitting/receiving frames
–
The prescaler is stopped, halting all related activities
–
The CPU can read and write into the Error counters register
–
TOUCAN ignores its Rx input pin and drives its Tx pins as recessive
–
TOUCAN loses synchronization with the CAN bus; the NTRDY and FRZAK
bits in MCR are set
After asserting the DEBUG mode configuration bits, the user must wait for the FRZAK bit in MCR
to be set before requesting any further actions from TOUCAN. Failure to adhere to this condition
may cause TOUCAN to operate in an unpredictable way.
Exiting the DEBUG mode is done in one of the following ways:
•
Both IMB3 FREEZE and HALT bits are negated
•
The CPU negates the FRZ1/FRZ0 mode bits
After exiting from DEBUG mode, TOUCAN will try to resynchronise with the CAN bus by waiting
for 11 consecutive recessive bits
B.20.2
STOP mode
The STOP mode in TOUCAN is intended for power saving. Before STOP mode is selected,
TOUCAN checks to see if either the CAN bus is in IDLE mode, or the third bit of intermission is a
recessive bit. If one of these conditions is met, TOUCAN waits for all internal activity (other than
that in the CAN bus interface) to finish and then the following steps take place:
–
TOUCAN shuts down its clocks, stopping most of the internal circuits. Thus
maximum power saving is achieved
–
The BIU logic continues operation, enabling CPU to access MCR
–
TOUCAN ignores its Rx input pin and drives its Tx pins as recessive
–
TOUCAN loses synchronization with the CAN bus; the STPAK and NTRDY
bits in MCR are set
MOTOROLA
B-16
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
149
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Exiting the STOP mode is done in one of the following ways:
•
Resetting TOUCAN (either by IMB3 hard reset, or by asserting the SFTRST bit in MCR
•
Negation of the STOP bit in MCR
•
Self-wake mechanism; if the SWAKE bit in MCR was set at the time TOUCAN entered STOP
mode, then upon detection of recessive-dominant transition on the CAN bus, TOUCAN resets
the STOP bit in MCR and resumes its clocks
When in STOP mode (or in LPSTOP), a recessive-dominant transition on the CAN bus causes the
WKINT bit in STATL to be set. This event can cause a CPU interrupt if the WKMSK bit in MCR is
set.
B.20.2.1 STOP mode operation notes
•
When in STOP/SELF_WAKE mode, TOUCAN tries to receive the frame that woke it up, i.e. it
assumes that the dominant bit detected is a start-of-frame bit. It does not arbitrate for the CAN
bus
•
Before asserting the STOP mode, the CPU should disable all interrupts in TOUCAN, otherwise
it may be interrupted while in STOP mode upon a non wake-up condition. If desired, the
WKMSK bit should be set to enable the WAKE_INT
•
If STOP is asserted while TOUCAN is BUSOFF (refer to Section B.25.1), then TOUCAN enters
STOP mode and stops counting the synchronization sequence. This count is continued when
STOP is negated
•
The correct procedure to enter STOP with self-wake is as follows
•
–
Assert SELF_WAKE at the same time as STOP
–
Wait for the STPAK bit to be set
The correct procedure to exit STOP with self-wake is as follows
–
Negate SELF_WAKE at the same time as STOP
–
Wait for the STPAK bit to be negated
•
SELF_WAKE should be set only when the STOP bit in MCR is negated and TOUCAN is ready
(i.e. when the NTRDY bit in MCR is negated)
•
if a recessive-dominant edge appears on the CAN bus immediately after STOP and
SELF_WAKE are set, then the STOP_ACK bit in MCR may never be set, and the STOP bit in
MCR is reset.
•
If it is undesirable to have old frames sent when TOUCAN is awakened, all Tx sources
(including remote response) should be disabled before STOP mode is entered
•
If DEBUG mode is active at the time of the STOP bit being asserted, then TOUCAN assumes
that the DEBUG mode should be exited; hence it tries to synchronize to the CAN bus (11
consecutive recessive bits), and only then does it search for the correct conditions to STOP.
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
B
MOTOROLA
B-17
150
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
•
Trying to STOP TOUCAN immediately after reset is allowed only after basic initialization has
been performed
•
If STOP with self-wake is activated, and TOUCAN operates with single system clock per
time-quanta, then there are extreme cases in which TOUCAN’s wake-up upon
recessive-dominant edge may not conform to the Bosch CAN protocol in that the TOUCAN
synchronization is shifted by one time quanta from that required. This shift lasts until the next
recessive-dominant edge, when TOUCAN is resynchronised to conform to the Protocol.
The same is also true for Auto Power Save mode (refer to Section B.20.3) upon wake-up by a
recessive-dominant edge.
B.20.3
Auto Power Save mode
This TOUCAN mode is intended to enable normal operation with optimized power saving. Upon
setting the AUTOPOWERSAVE bit in MCR, TOUCAN looks for a set of conditions in which there
is no need for clocks to be running. If all these conditions are met, then TOUCAN stops its clocks.
If, while its clocks are stopped, any of the conditions outlined below becomes untrue, then
TOUCAN resumes its clocks. It then continues to monitor the conditions and stops/resumes its
clocks accordingly.
The conditions for automatic clock shut off are:
–
No Rx/Tx frame in progress
–
No moving of Rx/Tx frames between SMB and message buffer, and no Tx
frame is pending for transmission in any message buffer
–
No host access to TOUCAN
–
TOUCAN is neither in DEBUG mode (MCR bit 8), in STOP mode (MCR bit
15) or in BUSOFF
B
MOTOROLA
B-18
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
151
Freescale Semiconductor, Inc.
B.20.4
Support BERR for RISC architechture (BERR_PLUG)
The TOUCAN supports the BERR behaviour according th o the IMB3 specification.
B.20.4.1 Modular family (BERR_PLUG = 0)
Freescale Semiconductor, Inc...
The TOUCAN never asserts the BERR signal in the IMB3.
B.20.4.2 RISC family (BERR_PLUG = 1)
The TOUCAN will terminate the cycle with BERR in the following cases:
•
access to unimplemented registers
•
user access to supervisor registers
•
write to read only registers
•
access to TCR register during normal mode
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-19
152
Freescale Semiconductor, Inc.
B.21
Interrupts
The TOUCAN supports two methods of Interrupt architecture, which can be chosen by a mask
programming option.
Freescale Semiconductor, Inc...
B.21.1
B
Modular family archtecture (IRQ_PLUG = 0)
The TOUCAN module is capable of generating one interrupt level on the IMB3. This level is
programmed into the Priority Level bits in the Interrupt Configuration Register. This value
determines which interrupt signal (IIRQB7-1) is driven onto the bus during an interrupt request.
When an interrupt is requested, the CPU initiates an IACK cycle. The module decodes the IACK
cycle and compares the CPU recognized level to the level that the module is currently requesting.
If a match occurs, then arbitration begins. During arbitration, the arbitration number is driven in bit
serial form, alternating between the IIARB0 and IIARB1 lines. The most significant bit of the
arbitration number is driven first. Since the bus is a wire-AND type, a ‘low’ level wins any
contentions. Thus the arbitration number is verified on a bit-by-bit basis. If contention is detected,
(driving high and detecting low), then the module has lost the arbitration and immediately stops
driving its arbitration number.
If the module wins the arbitration, it generates a uniquely encoded interrupt vector which indicates
which event is requesting service. This encoding scheme is as follows. The higher 3 bits of the
interrupt vector (called the Interrupt Vector Base Address) come from a 3-bit field of that name in
the Interrupt Configuration Register. The lower 5 bits are an encoded value (called the Interrupt
Source Number) and indicate which of the 19 interrupt sources is requesting service. Figure B-4
shows a block diagram of the interrupt hardware.
Interrupt
Request
Level
3
Interrupt
Level
Decoder
19
7
IIRQB[7:1]
Masks
Buffer
Interrupts
Bus-off
Error
16
Interrupt 19
Enable
Logic
Wake-up
Vector
Base
Address
(ICR[7:5])
Interrupt
Priority
Encoder
5 LSN
3 MSN
Module
Interrupt
Vector
3
Figure B-4 TOUCAN interrupt vector generation
MOTOROLA
B-20
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
153
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
Each one of the 16 message buffers can be an interrupt source, if its corresponding IMASK bit is
set. There is no distinction between Tx and Rx interrupts for a particular buffer, under the
assumption that the buffer is initialized for either transmission or receipt, and thus its interrupt
routine can be fixed at compilation time. Each of the buffers is assigned a bit in the
IFLAGH/IFLAGL register. The bit is set when the corresponding buffer completes a successful
transmission/receipt, and cleared when the CPU reads the interrupt flag register
(IFLAGH/IFLAGL) while the associated bit is set, and then writes it back as zero (and no new event
of the same type occurs between the read and the write actions). This is known as the Standard
Mechanism for IMB3 interrupts.
The other three interrupt sources (Bus-off, Error and Wake-up) act in the same way, and are
located in the Error and Status register. The Bus-off and Error interrupt mask bits are located in
the Control 0 register, and the Wake-up interrupt mask bit is located in the MCR.
Table B-4 Interrupt priorities and vector addresses
Name
IBUF0
IBUF1
IBUF2
IBUF3
IBUF4
IBUF5
IBUF6
IBUF7
IBUF8
IBUF9
IBUF10
IBUF11
IBUF12
IBUF13
IBUF14
IBUF15
IBOFF
IERROR
IWAKE
Note:
Function
Buffer0 interrupt
Buffer1 interrupt
Buffer2 interrupt
Buffer3 interrupt
Buffer4 interrupt
Buffer5 interrupt
Buffer6 interrupt
Buffer7 interrupt
Buffer8 interrupt
Buffer9 interrupt
Buffer10 interrupt
Buffer11 interrupt
Buffer12 interrupt
Buffer13 interrupt
Buffer14 interrupt
Buffer15 interrupt
Bus-off interrupt
Error interrupt
Wake-up interrupt
Vector address
$X0
$X1
$X2
$X3
$X4
$X5
$X6
$X7
$X8
$X9
$XA
$XB
$XC
$XD
$XE
$XF
$Y0
$Y1
$Y2 (Lowest priority)
B
X = bbb0
Y = bbb1
bbb = ICR[7:5]
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-21
154
Freescale Semiconductor, Inc.
B.21.2
RISC family architecture (IRQ_PLUG = 1)
Freescale Semiconductor, Inc...
The interrupt structure of the IMB3 supports a total of 32 interrupt levels that are time multiplexed
on the IRQB[0:7] lines as seen in Table B-5. In this structure, all interrupt sources place their
asserted level on a time multiplexed bus during four different time slots, with eight level
communicated per slot. (However, each group of levels actually occur, one system clock cycle after
the associated IMB3 IILBS signal is asserted). The ILBS[0:1] signals indicate which group of eight
are being driven on the interrupt request lines.
B
Table B-5 Interrupt levels
ILBS[1:0]
00
01
10
11
Levels
0:7
8:15
16:23
24:31
The TOUCAN modules is capable of generating 1 of 32 possible interrupt levels on the IMB3. The
level that the TOUCAN will drive can be programmed into the Interrupt Request Level bits located
in the Interrupt Configuration Register (IRL[2:0] bit field - bits [8:0] in the ICR register). The 2 bits
ILBS[1:0] in the ICR register (ILBS bit field - bits [7:6] in the ICR register) determine on which slot
the TOUCAN should drive its interrupt signal (one of IRQB[0-7]). Figure B-5 shows the timing of
slot multiplexing on the IMB3.
CLOCK
ILBS
IRQ
01
10
11
01
00
10
11
00
irq
irq
irq
irq
irq
irq
irq
7:0
15:8
23:16
31:24
7:0
15:8
23:16
Figure B-5 Int request multiplex timing
MOTOROLA
B-22
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
155
Freescale Semiconductor, Inc.
B.22
Programmer’s model
Freescale Semiconductor, Inc...
This section describes the registers and data structures in the TOUCAN module. The base
address of the module is hardware programmable as defined by the IMB3 Specification. The
address space occupied by TOUCAN is continuous: 128 bytes starting at the base address, and
256 extra bytes starting at the base address + 128. The upper 256 are fully used for the message
buffer structures. Only part of the lower 128 bytes is occupied by various registers.
The register decode map is fixed and begins at the first address of the Module Base Address.
Table B-5 shows the registers associated with the TOUCAN module and their relative offset from
the base address.
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-23
156
Freescale Semiconductor, Inc.
Table B-6 TOUCAN memory map
R/W
Access
Reset
Value
System Registers
Module Configuration Register
Test Configuration Register
Interrupt Configuration Register
R/W
Test
R/W
$5980
$0000
$000F
U
U
U
Control Registers
Control Register
Control & Prescaler Divider
Free Running Timer
R/W
R/W
R/W
$0000
$0000
$0000
$10
$12
$14
$16
$18
$1A
U
U
U
U
U
U
Rx Mask Registers
Rx Global Mask (high)
Rx Global Mask (low)
Rx Buffer 14 Mask (high)
Rx Buffer 14 Mask (low)
Rx Buffer 15 Mask (high)
Rx Buffer 15 Mask (low)
R/W
R/W
R/W
R/W
R/W
R/W
$FFEF
$FFFE
$FFEF
$FFFE
$FFEF
$FFFE
Error & Status
IMASK
IFLAGH/IFLAGL
Rx Err Cntr Tx Err Cntr
$20
$22
$24
$26
U
U
U
U
Global Info Registers
Error & Status
Interrupt Masks
Interrupt Flags
Rx & Tx Error counters
R/W
R/W
R/W
R/W
$0000
$0000
$0000
$0000
Control/status
ID_HIGH
ID_LOW
$80
$82
$84
$86
:
$8C
$8E
$90
U
Message Buffer 0
–
–
–
–
U
Message Buffer 1
U
Message Buffer 2.
–
–
Offset
S/U(1)
$00
$02
$04
S
S
S
$06
$08
$0A
RXGMASK_HIGH
RXGMASK_LOW
RX14MASK_HIGH
RX14MASK_LOW
RX15MASK_HIGH
RX15MASK_LOW
Freescale Semiconductor, Inc...
MCR
TCR
ICR
CTRL0
CTRL1
PRESDIV
CTRL2
TIMER
8 bytes data field
reserved
B
Register Function
$A0
—
—
—
—
—
—
$170
U
Message Buffer 15
(1) Supervisor/Unrestricted
MOTOROLA
B-24
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
157
Freescale Semiconductor, Inc.
B.22.1
Programming validity
Freescale Semiconductor, Inc...
Note that TOUCAN has no hard wired protection against invalid byte/field programming within its
registers; specifically, no protection is given in case the programming does not meet CAN protocol
requirement (for example, invalid bit segment values).
Also, programming TOUCAN control registers should be done at the initialization phase, prior to
TOUCAN becoming synchronized with the CAN bus, or after assertion of the HALT/FREEZE mode
while TOUCAN is in DEBUG state and NTRDY bit in MCR is set.
B.22.2
Reserved bits
In some cases the TOUCAN registers contain bit locations marked as ‘reserved’. These bits should
always be written as logic ‘0’.
B.22.3
System registers
These three registers (MCR, TCR, and ICR) define global configuration of the TOUCAN module,
such as interrupt level and base vector address, in addition to various operation modes (e.g. sleep)
and testing modes (e.g. internal logic visibility and controlability).
B.22.4
MCR — Module configuration register
Address bit 15
Module conÞguration register (MCR)
$00
$01
14
13
STOP
FRZ1
FRZ0
bit 7
6
5
12
11
10
9
bit 8
State
on reset
HALT NTRDY WKMSKSFTRST FRZAK 0101 1001
4
SUPV SWAKE PWRSV STPAK
3
2
1
0
IAI4
IAI3
IAI2
IAI1
1000 0000
STOP — Low power sleep mode
This bit may be set by the CPU, or negated by either the CPU or by TOUCAN if the SELF-WAKE
bit in MCR is set.
1 (set)
–
0 (clear) –
CAN PROTOCOL
Rev. 3
B
Shut down TOUCAN clocks.
Enable TOUCAN clocks.
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-25
158
Freescale Semiconductor, Inc.
FRZ1 — FREEZE enable bit 1
The FRZ1 bit specifies the TOUCAN response either to the FREEZE signal on the IMB3 being
asserted, or to the HALT bit in the MCR being asserted. This bit is initialised to ‘1’ during reset.
1 (set)
–
Freescale Semiconductor, Inc...
0 (clear) –
B
Refer to IMB3 FREEZE/HALT
Ignore FREEZE/HALT
When FRZ1 = 0, TOUCAN ignores both the FREEZE signal on the IMB3 and the HALT bit in the
MCR.
When FRZ1 = 1, it enables TOUCAN to enter the DEBUG HALT/FREEZE mode. In order to enter
this mode, the FRZ1 bit should be set to ‘1’, and either the IMB3 FREEZE line should be asserted,
or the HALT bit in MCR should be set. Negation of this bit field causes TOUCAN to exit from the
FREEZE/HALT mode. For further details refer to Section B.20.1.
FRZ0 — FREEZE enable bit 0
FRZ0 is not used in TOUCAN.
HALT — Halt TOUCAN Sclock
1 (set)
–
0 (clear) –
Enter DEBUG mode if FRZ1 = 1.
No TOUCAN internal request to enter DEBUG mode.
Assertion of this bit has the same effect as the assertion of the FREEZE signal on the IMB3, as
described in the FRZ1/FRZ0 sections above. However, it does not require that the FREEZE signal
be asserted in order to enter DEBUG mode.
The bit is initialized to ‘1’ (DEBUG mode). It is cleared by the CPU after the message buffers and
control registers have been initialized. When the HALT bit is asserted, the CPU also has
write-access to the error counters.
For a detailed description of the DEBUG mode, refer to Section B.20.1.
NTRDY — TOUCAN not ready
1 (set)
–
0 (clear) –
TOUCAN has entered either STOP or DEBUG mode.
TOUCAN has exited either STOP or DEBUG mode.
This bit indicates that TOUCAN is in either STOP or DEBUG mode. This bit is read only. Whenever
one of these two modes is asserted, this bit becomes set when TOUCAN enters that mode; it then
becomes negated only when TOUCAN exits the mode, either by synchronisation to the BUS (11
recessive bits) or by the self-wake mechanism. For further details refer to descriptions of the HALT,
FRZ1/FRZ0, FRZAK, STOP and STPAK bits in this section.
MOTOROLA
B-26
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
159
Freescale Semiconductor, Inc.
WKMSK — Wake-up interrupt mask
This bit enables the wake-up interrupt generation.
1 (set)
–
Wake-up interrupt enabled.
0 (clear) –
Wake-up interrupt disabled.
Freescale Semiconductor, Inc...
SFTRST — Soft reset
1 (set)
–
0 (clear) –
Request for soft reset initiated.
Normal operation.
After this bit is asserted, TOUCAN resets its internal machines (sequencer, error counters, error
flags, timer) and the host-interface registers (MCR, ICR, TCR, IMASK, IFLAGH/IFLAGL).
The configuration bits that control the interface with the CAN bus (CTRL0, CTRL1, CTRL2 and
PRESDIV) remain unchanged, as do the message buffers and the Rx message masks. This
enables the CPU to use the SFTRST as a debug feature during run-time of the system. SFTRST
also affects the MCR register, thus the STOP bit in MCR is reset, causing TOUCAN to resume its
clocks after coming out of STOP low-power mode.
Note that the next CPU access, after setting the SFTRST bit, should not be to TOUCAN, thus
allowing the TOUCAN internal circuitry to be fully reset. This bit is self-negated.
FRZAK — TOUCAN disabled and unsynchronised with CAN bus
1 (set)
–
0 (clear) –
TOUCAN is in DEBUG mode.
TOUCAN is not in DEBUG mode, and the prescaler is running.
FRZAK is a read-only bit which is set to ‘1’ when TOUCAN enters DEBUG mode, and ‘0’ when
DEBUG mode is negated and the prescaler is running.
When TOUCAN enters DEBUG mode, it sets the FRZAK bit. The CPU can poll this bit to find out
if TOUCAN entered DEBUG mode. If DEBUG mode is negated then FRZAK is also negated once
the TOUCAN prescaler is running. Refer also to the NTRDY bit in this section.
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-27
160
Freescale Semiconductor, Inc.
SUPV — Supervisor mode
Some registers on TOUCAN are always Supervisor data space, while others are programmable
as either Supervisor or Unrestricted data space by ignoring the FC2 line. This bit is concerned only
with the latter. The SUPV bit is initialised to logic ‘1’ during reset.
Freescale Semiconductor, Inc...
1 (set)
–
0 (clear) –
Assigned registers are restricted (FC2 line is decoded) and all
TOUCAN registers are placed in supervisor-only space. For any
access with a user data space function code, address acknowledge
(AACK) is not returned, and the bus cycle is transferred externally.
Assigned registers are unrestricted (FC2 line is ignored). AACK is
returned for accesses with either supervisor or user data space
function codes, and the cycle remains internal. If a supervisor-only
register is accessed with a user data space function code, the
module responds as though an access had been made to an
unimplemented register location.
SWAKE — Self wake up
1 (set)
–
Self wake-up enabled.
0 (clear) –
Self wake-up disabled.
This bit enables the self wake-up of TOUCAN after STOP, without CPU intervention. If this bit is
set when entering STOP, TOUCAN will look for a dominant bit on the bus during STOP. If a
recessive-dominant transition is detected, then TOUCAN will negate the STOP bit immediately and
resume the clocks.
This bit should be treated as a command, i.e. it is not always updated as written; the user should
verify if the value that has been written was captured in the register by reading MCR.
Note:
This bit should not be set if the LPSTOP command is executed. Fur further information
refer to Section B.20.2.
PWRSV — Auto power save
1 (set)
B
–
0 (clear) –
Auto power save mode active; clocks stop and resume when
required.
Auto power save mode not active; clocks run normally.
This bit enables TOUCAN to automatically shut off its clocks when it has no process to execute,
and then to resume them when it has a task to execute. There is no CPU intervention.
Note:
The BIU clocks are not stopped, thus enabling host access. Also, the auto power save
action does not depend on the values of SWAKE or WKMSK.
MOTOROLA
B-28
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
161
Freescale Semiconductor, Inc.
STPAK — TOUCAN stopped
1 (set)
–
0 (clear) –
TOUCAN is in STOP mode.
Normal TOUCAN operation exists.
Freescale Semiconductor, Inc...
This bit is read-only.
When TOUCAN enters STOP mode and shuts its clocks, STPAK becomes set. The CPU can poll
this bit to find out if TOUCAN entered STOP mode. If the STOP bit is negated then this bit is
negated once the TOUCAN clocks are running.
IAI[4:1] — Interrupt arbitration identifier
This four bit encoded field contains the interrupt arbitration number of this particular TOUCAN
module with respect to all other subsystems and peripherals that may generate interrupts. The
interrupt arbitration ID is used to arbitrate the IMB3 (relevant only when IRQ_PLUG = 0) when two
or more modules have an interrupt on the same priority level pending simultaneously. This field is
initialized to the non-arbitrating state, $0, during reset. If no arbitration takes place during the IACK
cycle, the spurious interrupt vector is generated after a time-out by the SIM module, alerting the
system to the fact that an interrupt arbitration ID has not been initialized.
B.22.5
TCR — Test configuration register
This register is for factory test purposes only.
B.22.6
ICR — Interrupt configuration register (Modular family
IRQ_PLUG = 0)
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Interrupt conÞguration (ICR) (high)
$04
0
0
0
0
0
IRQ3
IRQ2
IRQ1
0000 0000
Interrupt conÞguration (ICR) (low)
$05
IVB3
IVB2
IVB1
0
1
1
1
1
0000 1111
IRQ[3:1] — Interrupt request level
The interrupt request level field contains the priority level of the TOUCAN interrupts for the CPU,
where 111 indicates a nonmaskable interrupt, while 000 indicates that interrupts have been
disabled. If an interrupt flag is asserted and the corresponding mask bit is set to ‘1’, no interrupt is
generated unless the interrupt request level is a non-zero value. The interrupt request level field,
therefore, acts as master enable for the interrupts. The interrupt request level field is initialized to
zero during reset; this prevents the module from generating an interrupt until this register has been
initialized.
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
B
MOTOROLA
B-29
162
Freescale Semiconductor, Inc.
IVB[3:1] — Interrupt vector base address
The interrupt vector base address is specified by bits IVB[3:1]. This field specifies the most
significant nibble of all the vector numbers generated by the different TOUCAN interrupt sources.
This field is initialized to zero during reset.
Freescale Semiconductor, Inc...
ICR[4:0]
ICR[4:0] always read as ‘01111’. If TOUCAN issues an interrupt request after RESET and before
initializing the low byte of ICR, it will drive $0F as the interrupt vector, in response to a CPU
interrupt acknowledge cycle, regardless of the specific interrupt event. This is the ‘uninitialised
interrupt’ vector, as defined in the IMB3 specification and in the CPU16 reference manual.
B.22.7
ICR — Interrupt configuration register (RISC family
IRQ_PLUG = 1)
Address
Interrupt conÞguration (ICR) (high)
$04
Interrupt conÞguration (ICR) (low)
$05
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
0
0
0
0
0
IRL3
IRL2
IRL1
0000 0000
0
0
1
1
1
1
0000 1111
ILBS2 ILBS1
IRL[2:0] — Interrupt request level
The interrupt request level field contains the priority level of the TOUCAN interrupts for the CPU.
ILBS[1:0]
These bits indicate on which slot the TOUCAN should drive its interrupt..
Table B-7 Interrupt levels
ILBS[1:0]
00
01
10
11
B
MOTOROLA
B-30
Levels
0:7
8:15
16:23
24:31
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
163
Freescale Semiconductor, Inc.
B.23
Control registers
These registers provide control related to the CAN bus, such as bit-rate, programmable sampling
point within an Rx bit, and a global free-running timer.
Freescale Semiconductor, Inc...
B.23.1
CTRL0 — Control register 0
Control 0 (CTRL0)
Address
bit 7
bit 6
$06
BOFF
ERR
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
reserved reserved RXMD1 RXMD0 TXMD1 TXMD0 0000 0000
BOFF — Bus-off mask
This bit provides a mask for the bus-off interrupt.
1 (set)
–
Interrupt enabled.
0 (clear) –
Interrupt disabled.
ERR — Error mask
This bit provides a mask for the error interrupt.
1 (set)
–
Interrupt enabled.
0 (clear) –
Interrupt disabled.
RXMD[1,0] — Rx modes
Configuration control of the Rx0 pin.
RXMD1 is reserved; RXMD0 represents the polarity interpretation of Rx0. Operation of this bit is
as follows.
1 (set)
–
A dominant level is interpreted as a logical ‘1’; a recessive level is
interpreted as a logical 0.
0 (clear) –
A dominant level is interpreted as a logical ‘0’; a recessive level is
interpreted as a logical 1.
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-31
164
Freescale Semiconductor, Inc.
TXMD[1,0] — Tx modes
Configuration control of Tx0 and Tx1 pins. The operation of these bits is as shown in Table B-8.
Freescale Semiconductor, Inc...
Table B-8 Configuration control of Tx0, Tx1 pins
TXMD1 TXMD0
0
0
Full CMOS; positive polarity (i.e. Tx0=0, Tx1=1 is a dominant level)
0
1
Full CMOS; negative polarity (i.e. Tx0=1, Tx1=0 is a dominant level)
1
x
Open drain; positive polarity
Note:
“Full CMOS” drive means both dominant and recessive levels are driven by the chip.
“Open drain” drive means that only a dominant level is driven by the chip. During a
recessive level the Tx0, Tx1 pins are disabled (tri-state), and the electrical level is
achieved by external pull-up/pull-down devices.
The assertion of both Tx modes bits causes the polarity inversion to be cancelled, i.e.
open drain mode forces the polarity to be positive.
B.23.2
CTRL1 — Control register 1
Control 1 (CTRL1)
Address
bit 7
bit 6
bit 5
bit 4
$07
SAMP
LOOP
TSYNC
LBUF
bit 3
bit 2
bit 1
bit 0
State
on reset
reserved PROP2 PROP1 PROP0 0000 0000
SAMP — Sampling mode
1 (set)
–
0 (clear) –
Three samples are used to determine the value of the received bit;
the regular one (sample point) and two preceding samples, using a
majority rule.
One sample is used to determine the value of a received bit.
TSYNC — Timer synchronise mode
1 (set)
B
–
Timer synchronise enabled.
0 (clear) –
Timer synchronise disabled.
This bit enables a mechanism that resets (clears) the free-running timer each time a message is
received in MB0. This feature provides means to synchronize multiple TOUCAN stations with a
special “SYNC” message (i.e., global network time). A buffer0 interrupt is also available.
Note:
There is a possibility of a 4-5 tick count skew between the different TOUCAN stations
that would operate this mode.
MOTOROLA
B-32
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
165
Freescale Semiconductor, Inc.
LBUF — Lowest buffer transmitted first
This bit defines the transmit-first scheme.
1 (set)
–
0 (clear) –
Lowest buffer is transmitted first.
Lowest ID is transmitted first.
Freescale Semiconductor, Inc...
Bit 3 — Reserved
Caution: This bit must not be written as ‘1’.
PROPSEG[2:0] — Propagation segment
This field defines the length of the propagation segment in the bit time. The valid programmed
values are 0-7.
Propagation segment time = (PROPSEG + 1) * Time-Quanta
(time-quanta = 1 Sclock. Refer to Section B.23.3.)
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-33
166
Freescale Semiconductor, Inc.
B.23.3
PRESDIV — Prescaler divide register
Prescale divide (PRESDIV)
Address
bit 15
bit 14
bit 13
bit 12
bit 11
bit 10
bit 9
bit 8
State
on reset
$08
(bit 15)
(14)
(13)
(12)
(11)
(10)
(9)
(bit 8)
0000 0000
Freescale Semiconductor, Inc...
PRESDIV[15:8]
B
This field determines the ratio between the system clock frequency and the Sclock (Serial clock).
(1 Sclock = 1 time quantum).
The Sclock is equal to the system clock divided by (value of this register + 1).
The reset value of this register is $0000, which means that the Sclock is the same as the system
clock frequency.
The maximum value of this 8-bit register is $FF, which gives the minimum Sclock frequency of
(system clock/256). For a 16MHz system clock, this gives a 64kHz Sclock, which can operate a
CAN bit rate of 8K bit/s. For further information refer to Section B.17.
B.23.4
CTRL2 — Control register 2
Control 2 (CTRL2)
Address
bit 7
$09
RJW1
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
RJW0 PSEG12 PSEG11 PSEG10 PSEG22 PSEG21 PSEG20 0000 0000
RJW[1:0] — Resynchronise jump width
This field defines the maximum number of time quanta a bit time may be changed by one
resynchronisation. The valid programmed values are 00-11.
Resynchronise jump width = RJW value + 1
PSEG1[2:0] — Phase segment 1
This field defines the length of phase buffer segment 1 in the bit time.
The valid programmed values are 000-111.
Phase buffer segment 1 = (PSEG1 + 1) x Time quanta
PSEG2[2:0] — Phase segment 2
This field defines the length of phase buffer segment 2 in the bit time.
The valid programmed values are 000-111.
Phase buffer segment 2 = (PSEG2 + 1) x Time quanta
MOTOROLA
B-34
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
167
Freescale Semiconductor, Inc.
B.23.5
TIMER — Free running timer
Address
Freescale Semiconductor, Inc...
Free running timer (TIMER)
$0A
bit 1
bit 0
State
on reset
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
(bit 15)
(14)
(13)
(12)
(11)
(10)
(9)
(bit 8) 0000 0000
(bit 7)
(6)
(5)
(4)
(3)
(2)
(1)
(bit 0) 0000 0000
This is a 16-bit free running counter which can be read and written by the CPU. The timer starts
from $0000 after reset, counts linearly to $FFFF, and wraps around.
This timer is clocked by the TOUCAN bit-clock. During a message it increments by one for each
bit that is received or transmitted. When there is no message on the bus it counts the nominal bit
rate.
The timer value is captured at the beginning of the ID field of any frame on the CAN bus; this value
is then written into the TIME STAMP entry in a message buffer after a successful
receipt/transmission of a message.
B.24
Rx mask registers
These registers are used as acceptance masks for received frame ID’s. Three masks are defined:
a global mask, used for all Rx buffers 0-13, and two separate masks for buffers 14 and 15. The
following applies for all the mask bits within these registers.
1 (set)
–
0 (clear) –
Note:
The corresponding ID bit is checked against the incoming ID bit, to
see if a match exists.
The corresponding incoming ID bit is ‘don’t care’.
These masks are used for both standard and extended ID formats. The value of mask
registers should not be changed while in normal operation, as locked frames which
matched a message buffer through a mask may be transferred into the message buffer
(upon release) but may no longer match. Refer to Table B-9.
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-35
168
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Table B-9 Mask examples for normal/extended messages
Base ID
ID28...ID18
11111111000
11111111000
00000011111
00000011101
11111111000
11111111110
11111111001
11111111001
11111111001
01111111000
01111111000
01111111111
10111111000
01111111000
MB2 - ID
MB3 - ID
MB4 - ID
MB5 - ID
MB14 - ID
Rx global mask
Rx_msg in
Rx_msg in
Rx_msg in
Rx_msg in
Rx_msg in
Rx_14_mask
Rx_msg in
Rx_msg in
Extended ID
ID17...ID0
IDE
0
1
0
1
1
1
0
1
0
1
1
1
Match
010101010101010101
010101010101010101
010101010101010101
111111100000000001
010101010101010101
3
2
(1)
(2)
(3)
010101010101010101
(4)
010101010101010101
111111100000000000
010101010101010101
010101010101010101
(5)
(6)
14
(7)
(1) Match for extended format (MB3).
(2) Match for standard format (MB2).
(3) Un-match for MB3 because of ID0.
(4) Un-match for MB2 because of ID28.
(5) Un-match for MB3 because of ID28; match for MB14.
(6) Un-match for MB14 because of ID27.
(7) Match for MB14.
B.24.1
RXMASK — Rx global mask register
B
Rx global mask (RXMASK)
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$10
MID28
MID27
MID26
MID25
MID24
MID23
MID22
MID21
1111 1111
$11
MID20
MID19
MID18
0
1
MID17
MID16
MID15
1110 1111
$12
MID14
MID13
MID12
MID11
MID10
MID9
MID8
MID7
1111 1111
$13
MID6
MID5
MID4
MID3
MID2
MID1
MID0
0
1111 1110
The Rx global mask registers are composed of 4 bytes. The mask bits are applied to all Rx
identifiers excluding Rx buffers 14-15 which have their specific Rx mask registers.
MOTOROLA
B-36
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
169
Freescale Semiconductor, Inc.
Base ID: ID28-ID18
These bits are the same mask bits for standard or extended format.
Extended ID: ID17-ID0
These bits are used to mask comparison only in extended format.
Freescale Semiconductor, Inc...
RTR/SRR (bits 20 and 0)
The RTR bit of a received frame is never compared to the corresponding bit in the message buffer
ID field. Also, remote request frames are never received into message buffers. These bits are
always ‘0’, regardless of any CPU write to these bits.
IDE
The IDE bit of a received frame is always compared. This bit is always ‘1’, regardless of any CPU
write to this bit.
B.24.2
RX14MASK — Rx buffer 14 mask
The Rx buffer 14 mask register has the same structure as the Rx global mask register and is used
to mask buffer 14. The register is located at address $14-$17.
B.24.3
RX15MASK — Rx buffer 15 mask
The Rx buffer 15 mask register has the same structure as the Rx global mask register and is used
to mask buffer 15. The register is located at address $18-$1B.
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-37
170
Freescale Semiconductor, Inc.
B.25
Global information registers
To negate an interrupt flag, the flag must first be read as ‘1’ and then written as ‘0’. For future
reference, this method of negating the interrupt flag is referred to as the Motorola Standard
Mechanism.
Freescale Semiconductor, Inc...
B.25.1
B
STATH, STATL — Error and status report registers
Address bit 15
14
13
12
11
10
9
bit 8
State
on reset
Error and status report high (STATH)
$0070 B1ERR B0ERR ACKER CRCER FMERR STERR TXWRN RXWRN 0000 0000
Error and status report low (STATL)
$0071
bit 7
6
IDLE
TX/RX
5
4
BUS_STATE
3
0
2
1
0
BOFINT ERRINT WKINT 0000 0000
These registers include error condition information, general status information and three interrupt
sources. The reported error conditions are those which have occurred since the last time the
register was read. These bits are cleared after a read.
All bits in STATH and STATL are read-only, except for the interrupt sources (BOFINT, ERRINT,
WKINT). For further information refer to Section B.21 (Interrupts).
Table B-10 Bit error status
B1ERR/B0ERR
00
01
10
11
Bit error status
No transmit error
At least one bit sent as dominant is received as recessive
At least one bit sent as recessive is received as dominant
Not used
B1ERR — Bit 1 error bit See Table B-10 for details
Note:
This bit is not set by a transmitter in the case of an arbitration field or ACK slot, or in the
case of a node sending a passive error flag that detects dominant bits.
MOTOROLA
B-38
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
171
Freescale Semiconductor, Inc.
B0ERR — Bit 0 error bit See Table B-10 for details
ACKER — ACK error
1 (set)
–
An ACK error has occurred since the last read of this register.
0 (clear) –
No ACK error has occurred since the last read of this register.
Freescale Semiconductor, Inc...
CRCER — CRC error
1 (set)
–
0 (clear) –
A CRC error has occurred since the last read of this register.
No CRC error has occurred since the last read of this register.
FMERR — FORM error
1 (set)
–
0 (clear) –
A FORM error has occurred since the last read of this register.
No FORM error has occurred since the last read of this register.
STERR — STUFF error
1 (set)
–
0 (clear) –
A STUFF error has occurred since the last read of this register.
No STUFF error has occurred since the last read of this register.
TXWRN — Tx warn
–
Tx_Error_Counter ≥ 96.
0 (clear) –
Tx_Error_Counter < 96.
1 (set)
This status flag does not cause an interrupt.
RXWRN — Rx warn
–
Rx_Error_Counter ≥ 96.
0 (clear) –
Rx_Error_Counter < 96.
1 (set)
This status flag does not cause an interrupt.
IDLE
1 (set)
–
0 (clear) –
B
The CAN bus is now idle.
The CAN bus is not idle.
TX/RX — Transmit/receive
1 (set)
–
0 (clear) –
CAN PROTOCOL
Rev. 3
TOUCAN is transmitting a message if IDLE = ‘0’.
TOUCAN is receiving a message if IDLE = ‘0’.
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-39
172
Freescale Semiconductor, Inc.
This bit has no meaning in the case where IDLE = ‘1’.
BUS_STATE — Fault confinement state
This two-bit field describes the state of TOUCAN:
Freescale Semiconductor, Inc...
Table B-11 Fault confinement sate of TOUCAN
B
Bit 5
0
0
1
Bit 4
0
1
x
State
Error active
Error passive
BUSOFF
If SFTRST in MCR is asserted while TOUCAN is in BUSOFF state, then STATH and STATL are
reset (including the BUS_STATE bits), but when exiting the DEBUG mode state, the BUS_STATE
bits return to reflect the BUSOFF state.
BOFINT — Bus off interrupt
1 (set)
–
0 (clear) –
TOUCAN’s bus state has changed to BUSOFF.
No such occurrence.
Each time the TOUCAN state changes to BUSOFF, this bit is set, and if the corresponding mask
bit (BOFF) is set, an interrupt is generated. This interrupt is not generated after reset. Use of the
Motorola Standard Mechanism is required to reset this flag to ‘0’ and negate its corresponding
interrupt. Writing a ‘1’ to this bit has no effect.
ERRINT — Error interrupt
1 (set)
–
0 (clear) –
TOUCAN has detected a CAN bus error or one of the error conditions
has been set.
No such occurrence.
Each time one of the error bits (bits 15:10) is set (even if already set), this bit is set, and if the ERR
bit in CTRL0 is set, an interrupt is generated to the host. Using the Motorola Standard Mechanism
is required to reset this flag to ‘0’ and negate its corresponding interrupt. Writing a ‘1’ to this bit has
no effect.
WKINT — Wake interrupt
1 (set)
–
0 (clear) –
MOTOROLA
B-40
Recessive to dominant transition event has occurred on the CAN bus
when in STOP mode.
No such occurrence.
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
173
Freescale Semiconductor, Inc.
If a recessive to dominant transition is detected on the CAN bus while TOUCAN is in low-power
SLEEP mode (STOP=1 in MCR), and if WKMSK bit in MCR is set, then this bit becomes set and
an interrupt is generated to the CPU. Refer to Section B.22.4 (Module Configuration Register
(MCR)) for further details. Using the Motorola Standard Mechanism is required to reset this flag to
‘0’ and negate its corresponding interrupt. Writing a ‘1’ to this bit has no effect.
Freescale Semiconductor, Inc...
B.25.2
IMASKH, IMASKL— Interrupt mask registers
Address
bit 15
14
13
12
11
10
9
bit 8
State
on reset
Interrupt mask high (IMASKH)
$0022 BUF15M BUF14M BUF13M BUF12M BUF11M BUF10M BUF9M BUF8M 0000 0000
Interrupt mask low (IMASKL)
$0023
bit 7
6
5
4
3
2
1
0
BUF7M BUF6M BUF5M BUF4M BUF3M BUF2, BUF1M BUF0M 0000 0000
Caution: Setting or clearing a bit in the IMASKH/IMASKL register can assert or negate an
interrupt request, respectively.
This register contains one interrupt mask bit per buffer. It enables the CPU to determine which
buffer will generate an interrupt after a successful transmission/receipt (i.e. when the
corresponding IFLAGH/IFLAGL bit is set).
IMASKH and IMASKL contain two 8-bit fields: bits 15-8 (IMASKH) and bits 7-0 (IMASKL). The
register can be accessed by the master as a 16-bit register, or each byte can be accessed
individually using an 8-bit (1 byte) access cycle.
BUFM[15:0]
1 (set)
–
The corresponding buffer interrupt is enabled.
0 (clear) –
The corresponding buffer interrupt is disabled.
B.25.3
IFLAGH, IFLAGL — Interrupt flag registers
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Interrupt ßag high (IFLAGH)
$0024 BUF15l BUF14l BUF13l BUF12l BUF11l BUF10l BUF9l BUF8l 0000 0000
Interrupt ßag low (IFLAGL)
$0025
B
BUF7l BUF6l BUF5l BUF4l BUF3l BUF2l BUF1l BUF0l 0000 0000
The interrupt flag registers contain one interrupt flag bit per buffer. Each successful
transmission/receipt sets the corresponding IFLAG bit and, if the corresponding IMASK bit is set,
will generate an interrupt.
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-41
174
Freescale Semiconductor, Inc.
The register contains two 8-bit fields: bits 15-8 (IFLAG_H) and bits 7-0 (IFLAG_L). The register can
be accessed by the master as a 16-bit register, or each byte can be accessed individually using
an 8-bit (1 byte) access cycle.
IBUFl[15:0]
Freescale Semiconductor, Inc...
1 (set)
B
–
0 (clear) –
The corresponding buffer has successfully completed transmission
or receipt.
The corresponding buffer has not completed transmission or receipt.
Should a new interrupt occur between the time that the CPU reads the flag as ‘1’ and writes the
flag as ‘0’ to clear it, the flag will not be cleared in order to indicate the new interrupt request. The
register is initialized to zero during reset. This register is writeable to ‘0’s only, as defined in the
standard mechanism.
B.25.4
Error counters
State
on reset
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
Rx Error Counter
$26
(bit 15)
(14)
(13)
(12)
(11)
(10)
(9)
(bit 8) 0000 0000
Tx Error Counter
$27
(bit 7)
(6)
(5)
(4)
(3)
(2)
(1)
(bit 0) 0000 0000
There are two error counters in TOUCAN; transmit error counter and receive error counter. The
rules for increasing and decreasing these counters are described in the CAN Protocol
Specification, Version 2.0 and are fully implemented in TOUCAN. Each counter comprises the
following.
•
8-bit up/down counter
•
Increment by 8 (Rx_Err_Counter also by 1)
•
Decrement by 1
•
Avoid decrement when equal to zero
•
Rx_Err_Counter preset to a value 119 ≤ x ≤ 127
•
Value after reset = zero
•
Detect values for error_passive, error_active and BUSOFF transitions and for alerting the host
•
Cascade usage of Tx_Err_Counter with an internal other counter to detect the 128
occurrences of 11 consecutive recessive bits to determine move from Bus-Off into
error_active.
Both counters are read only (except for Test/Freeze/halt modes).
MOTOROLA
B-42
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
175
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
TOUCAN responds to any bus state as described in the protocol, e.g. transmit error active or error
passive flag, delay its transmission start time (Error Passive) and avoid any influence on the bus
when in Bus Off state. The following are the basic rules for TOUCAN bus state transitions:
•
If the value of Tx_Err_Counter or Rx_Err_Counter becomes ≥ 128, the BUS_STATE field in the
Error Status Register is updated to reflect this (Error Passive state is set).
•
If the TOUCAN state is Error Passive, and either the Tx_Err_Counter counter or the
Rx_Err_Counter becomes ≤ 127 while the other already satisfies this condition, the
BUS_STATE field in the Error Status Register is updated to reflect this (Error Active state is
set).
•
If the value of the Tx_Err_Counter increases to be greater than or equal to 256, the
BUS_STATE field in the Error Status Register is updated to reflect it (set BUSOFF state) and
an interrupt may be issued. The value of Tx_Error_Counter is then reset to zero.
•
If the TOUCAN state is BUSOFF, then Tx_Error_Counter, together with an internal counter are
cascaded to count the 128 occurrences of 11 consecutive recessive bits on the bus. Hence,
Tx_Error_Counter is reset to zero, and counts in a manner where the internal counter counts
11 such bits and then wraps around while incrementing the Tx_Err_Counter. When
Tx_Err_Counter reaches the value of 128, BUS_STATE field in the Error Status Register is
updated to be Error Active, and both error counters are reset to zero. At any instance of
dominant bit following a stream of less than 11 consecutive recessive bits, the internal counter
resets itself to zero, but does NOT affect the Tx_Err_Counter value.
•
If during system start-up, only one node is operating, then its Tx_Err_Counter increases each
message it’s trying to transmit, as a result of ACK_ERROR. A transition to bus state Error
Passive should be executed as described, while this device never enters the BUSOFF state.
•
If the Rx_Err_Counter increases to a value greater than 127, it is prevented from being
increased any further, even if more errors are detected while being a receiver. At the next
successful message receipt, the counter is set to a value between 119 and 127, to enable Error
Active state to be resumed.
B
CAN PROTOCOL
Rev. 3
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
B-43
176
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
THIS PAGE LEFT BLANK INTENTIONALLY
B
MOTOROLA
B-44
TOUCAN
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
177
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
C
THE MOTOROLA SCALEABLE CAN
(MSCAN08) MODULE
The MSCAN08 is the specific implementation of the Motorola Scalable CAN (MSCAN) concept
targeted for the Motorola M68HC08 Microcontroller Family.
The module is a communication controller implementing the CAN 2.0 A/B protocol as defined in
the BOSCH specification dated September 1991.
The CAN protocol was primarily, but not only, designed to be used as a vehicle serial data bus,
meeting the specific requirements of this field: real-time processing, reliable operation in the EMI
environment of a vehicle, cost-effectiveness and required bandwidth.
MSCAN08 utilises an advanced buffer arrangement resulting in a predictable real-time behaviour
and simplifies the application software.
C.1
Features
The basic features of the MSCAN08 are as follows:
•
Modular Architecture
•
Implementation of the CAN protocol - Version 2.0A/B
–
Standard and extended data frames.
–
0 - 8 bytes data length.
–
Programmable bit rate up to 1 Mbps†.
•
Support for Remote Frames.
•
Double buffered receive storage scheme.
•
Triple buffered transmit storage scheme with internal priorisation using a local priority concept.
†
C
Depending on the actual bit timing and the clock jitter of the PLL.
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-1
178
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
•
Flexible maskable identifier filter supports alternatively one full size extended identifier filter or
two 16 bit filters or four 8 bit filters.
•
Programmable wake-up functionality with integrated low-pass filter.
•
Programmable Loop-Back mode supports self-test operation.
•
Separate signalling and interrupt capabilities for all CAN receiver and transmitter error states
(Warning, Error Passive, Bus-Off).
•
Programmable MSCAN08 clock source either CPU bus clock or crystal oscillator output.
•
Programmable link to on-chip Timer Interface Module (TIM) for time-stamping and network
synchronisation.
•
Low power sleep mode.
C
TPG
MOTOROLA
C-2
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
179
Freescale Semiconductor, Inc.
C.2
External Pins
The MSCAN08 uses 2 external pins, 1 input (RxCAN) and 1 output (TxCAN). The TxCAN output
pin represents the logic level on the CAN: ‘0’ is for a dominant state, and ‘1’ is for a recessive state.
A typical CAN system with MSCAN08 is shown in Figure C-1.
Freescale Semiconductor, Inc...
CAN station 1
CAN node 1
CAN node 2
CAN node n
MCU
CAN Controller
(MSCAN08)
TxCAN
RxCAN
Transceiver
CAN_H
CAN_L
C A N - Bus
Figure C-1 The CAN System
Each CAN station is connected physically to the CAN bus lines through a transceiver chip. The
transceiver is capable of driving the large current needed for the CAN and has current protection,
against defected CAN or defected stations.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-3
180
Freescale Semiconductor, Inc.
C.3
Message Storage
MSCAN08 facilitates a sophisticated message storage system which addresses the requirements
of a broad range of network applications.
Freescale Semiconductor, Inc...
C.3.1
Background
Modern application layer software is built under two fundamental assumptions:
1) Any CAN node is able to send out a stream of scheduled messages without
releasing the bus between two messages. Such nodes will arbitrate for the
bus right after sending the previous message and will only release the bus
in case of lost arbitration.
2) The internal message queue within any CAN node is organized as such that
the highest priority message will be sent out first if more than one message
is ready to be sent.
The above behaviour can not be achieved with a single transmit buffer. That buffer must be
reloaded right after the previous message has been sent. This loading process lasts a definite
amount of time and has to be completed within the Inter-Frame Sequence (IFS) in order to be able
to send an uninterrupted stream of messages. Even if this is feasible for limited CAN bus speeds
it requires that the CPU reacts with short latencies to the transmit interrupt.
A double buffer scheme would de-couple the re-loading of the transmit buffers from the actual
message sending and as such reduces the reactiveness requirements on the CPU. Problems may
arise if the sending of a message would be finished just while the CPU re-loads the second buffer,
no buffer would then be ready for transmission and the bus would be released.
At least three transmit buffers are required to meet the first of above requirements under all
circumstances. The MSCAN08 has three transmit buffers.
The second requirement calls for some sort of internal priorisation which the MSCAN08
implements with the “local priority” concept described below.
C
TPG
MOTOROLA
C-4
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
181
Freescale Semiconductor, Inc.
C.3.2
Receive Structures
Freescale Semiconductor, Inc...
The received messages are stored in a two stage input FIFO. The two message buffers are
mapped using a ‘ping pong’ arrangement into a single memory area (see Figure C-2). While the
background receive buffer (RxBG) is exclusively associated to the MSCAN08, the foreground
receive buffer (RxFG) is addressable by the CPU08. This scheme simplifies the handler software
as only one address area is applicable for the receive process.
Both buffers have a size of 13 byte to store the CAN control bits, the identifier (standard or
extended) and the data content (for details see Section C.11).
The Receiver Full flag (RXF) in the MSCAN08 Receiver Flag Register (CRFLG) (see
Section C.12.6) signals the status of the foreground receive buffer. When the buffer contains a
correctly received message with matching identifier this flag is set.
After the MSCAN08 successfully received a message into the background buffer it copies the
content of RxBG into RxFG†, sets the RXF flag, and emits a receive interrupt to the CPU‡. A new
message - which may follow immediately after the IFS field of the CAN frame - will be received into
RxBG.
The user’s receive handler has to read the received message from RxFG and to reset the RXF flag
in order to acknowledge the interrupt and to release the foreground buffer.
An overrun conditions occurs when both the foreground and the background receive message
buffers are filled with correctly received messages, and a further message is being received from
the bus. The latter message will be discarded and an error interrupt with overrun indication will
occur if enabled. The over-writing of the background buffer is independent of the identifier filter
function. While in the overrun situation, the MSCAN08 will stay synchronized to the CAN bus and
is able to transmit messages but will discard all incoming messages.
Note:
MSCAN08 will receive its own messages into the background receive buffer RxBG but
will NOT overwrite RxFG and will NOT emit a receive interrupt nor will it acknowledge
(ACK) its own messages on the CAN bus. The exception to this rule is that when in
loop-back mode MSCAN08 will treat its own messages exactly like all other incoming
messages.
†
Only if the RXF flag is not set.
‡
The receive interrupt will occur only if not masked. A polling scheme can be applied on RXF
also.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-5
182
Freescale Semiconductor, Inc.
MSCAN08
CPU08 bus
RxBG
Freescale Semiconductor, Inc...
RxFG RXF
Tx0
TXE
PRIO
Tx1
TXE
PRIO
Tx2
TXE
PRIO
Figure C-2 User Model for Message Buffer Organization
C
TPG
MOTOROLA
C-6
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
183
Freescale Semiconductor, Inc.
C.3.3
Transmit Structures
Freescale Semiconductor, Inc...
The MSCAN08 has a triple transmit buffer scheme in order to allow multiple messages to be set
up in advance and to achieve an optimized real-time performance. The three buffers are arranged
as shown in Figure C-2.
All three buffers have a 13 byte data structure similar to the outline of the receive buffers (see
Section C.11). An additional Transmit Buffer Priority Register (TBPR) contains an 8-bit so called
Local Priority field (PRIO) (see Section C.11.5).
In order to transmit a message, the CPU08 has to identify an available transmit buffer which is
indicated by a set Transmit Buffer Empty (TXE) Flag in the MSCAN08 Transmitter Flag Register
(CTFLG) (see Section C.12.8).
The CPU08 then stores the Identifier, the control bits and the data content into one of the transmit
buffers. Finally, the buffer has to be flagged as being ready for transmission by clearing the TXE
flag.
The MSCAN08 will then schedule the message for transmission and will signal the successful
transmission of the buffer by setting the TXE flag. A transmit interrupt will be emitted† when TXE
is set and can be used to drive the application software to re-load the buffer.
In case more than one buffer is scheduled for transmission when the CAN bus becomes available
for arbitration, the MSCAN08 uses the local priority setting of the three buffers for priorisation. For
this purpose every transmit buffer has an 8-bit local priority field (PRIO). The application software
sets this field when the message is set up. The local priority reflects the priority of this particular
message relative to the set of messages being emitted from this node. The lowest binary value of
the PRIO field is defined to be the highest priority.
The internal scheduling process takes places whenever the MSCAN08 arbitrates for the bus. This
is also the case after the occurrence of a transmission error.
When a high priority message is scheduled by the application software it may become necessary
to abort a lower priority message being set up in one of the three transmit buffers. As messages
that are already under transmission can not be aborted, the user has to request the abort by
setting the corresponding Abort Request Flag (ABTRQ) in the Transmission Control Register
(CTCR). The MSCAN08 will then grant the request if possible by setting the corresponding Abort
Request Acknowledge (ABTAK) and the TXE flag in order to release the buffer and by emitting a
transmit interrupt. The transmit interrupt handler software can tell from the setting of the ABTAK
flag whether the message was actually aborted (ABTAK=1) or has been sent in the meantime
(ABTAK=0).
†
The transmit interrupt will occur only if not masked. A polling scheme can be applied on TXE
also.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-7
184
Freescale Semiconductor, Inc.
C.4
Identifier acceptance Filter
Freescale Semiconductor, Inc...
A very flexible programmable generic identifier acceptance filter has been introduced in order to
reduce the CPU interrupt loading. The filter is programmable to operate in three different modes:
•
Single identifier acceptance filter to be applied to the full 29 bits of the identifier and to the
following bits of the CAN frame: RTR, IDE, SRR. This mode implements a single filter for a full
length CAN 2.0B compliant extended identifier.
•
Double identifier acceptance filter to be applied to
•
–
the 11 bits of the identifier and the RTR bit of CAN 2.0A mesages or
–
the 14 most significant bits of the identifier of CAN 2.0B messages.
Quadruple identifier acceptance filter to be applied to the first 8 bits of the identifier. This mode
implements four independent filters for the first 8 bit of a CAN 2.0A compliant standard
identifier.
The Identifier Acceptance Registers (CIAR) defines the acceptable pattern of the standard or
extended identifier (ID10 - ID0 or ID28 - ID0). Any of these bits can be marked don’t care in the
Identifier Mask Register (CIMR).
ID28
IDR0
ID21 ID20
ID10
IDR0
ID3 ID2
IDR1
ID15 ID14
IDR1 IDE
IDR2
ID7 ID6
IDR3
RTR
ID10 IDR2 ID3 ID10 IDR3 ID3
AM7 CIDMR0 AM0 AM7 CIDMR1 AM0 AM7 CIDMR2 AM0 AM7 CIDMR3 AM0
AC7 CIDAR0 AC0 AC7 CIDAR1 AC0 AC7 CIDAR2 AC0 AC7 CIDAR3 AC0
ID Accepted (Filter 0 Hit)
Figure C-3 Single 32 bit Maskable Identifier Acceptance Filter
The background buffer RxBG will be copied into the foreground buffer RxFG and the RXF flag will
be set only in case of an accepted identifier (an identifier acceptance filter hit). A hit will also cause
a receiver interrupt if enabled.
C
TPG
MOTOROLA
C-8
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
185
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
ID28
IDR0 ID21 ID20
IDR1 ID15 ID14
ID10
IDR0
IDR1 IDE
ID3 ID2
IDR2
ID7 ID6
IDR3
RTR
ID10 IDR2 ID3 ID10 IDR3 ID3
AM7 CIDMR0 AM0 AM7 CIDMR1 AM0
AC7 CIDAR0 AC0 AC7 CIDAR1 AC0
ID Accepted (Filter 0 Hit)
AM7 CIDMR2 AM0 AM7 CIDMR3 AM0
AC7 CIDAR2 AC0 AC7 CIDAR3 AC0
ID Accepted (Filter 1 Hit)
Figure C-4 Dual 16 bit Maskable Acceptance Filters
A filter hit is indicated to the application software by a set RXF (Receive Buffer Full Flag, see
Section C.12.6) and two bits in the Identifier Acceptance Control Register (see Section C.12.10).
These Identifier Hit Flags (IDHIT1-0) clearly identify the filter section that caused the acceptance.
They simplify the application software’s task to identify the cause of the receiver interrupt. In case
that more than one hit occurs (two or more filters match) the lower hit has priority.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-9
186
Freescale Semiconductor, Inc.
ID28 IDR0 ID21 ID20 IDR1 ID15 ID14 IDR2 ID7 ID6 IDR3 RTR
ID10 IDR0 ID3 ID2 IDR1 IDE
ID10 IDR2 ID3 ID10 IDR3 ID3
Freescale Semiconductor, Inc...
AM7 CIDMR0AM0
AC7 CIDAR0 AC0
ID Accepted (Filter 0 Hit)
AM7 CIDMR1AM0
AC7 CIDAR1 AC0
ID Accepted (Filter 1 Hit)
AM7 CIDMR2AM0
AC7 CIDAR2 AC0
ID Accepted (Filter 2 Hit)
AM7 CIDMR3AM0
AC7 CIDAR3 AC0
ID Accepted (Filter 3 Hit)
Figure C-5 Quadruple 8 bit Maskable Acceptance Filters
C
TPG
MOTOROLA
C-10
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
187
Freescale Semiconductor, Inc.
C.5
Interrupts
Freescale Semiconductor, Inc...
The MSCAN08 supports four interrupt vectors mapped onto eleven different interrupt sources, any
of which can be individually masked (for details see Section C.12.6 to Section C.12.9):
•
Transmit Interrupt: At least one of the three transmit buffers is empty (not scheduled) and can
be loaded to schedule a message for transmission. The TXE flags of the empty message
buffers are set.
•
Receive Interrupt: A message has been successfully received and loaded into the foreground
receive buffer. This interrupt will be emitted immediately after receiving the EOF symbol. The
RXF flag is set.
•
Wake-Up Interrupt: An activity on the CAN bus occurred during MSCAN08 internal sleep
mode.
•
Error Interrupt: An overrun, error or warning condition occurred. The Receiver Flag Register
(CRFLG) will indicate one of the following conditions:
–
Overrun: An overrun condition as described in Section C.3.2 has occurred.
–
Receiver Warning: The Receive Error Counter has reached the CPU
Warning limit of 96.
–
Transmitter Warning: The Transmit Error Counter has reached the CPU
Warning limit of 96.
–
Receiver Error Passive: The Receive Error Counter has exceeded the Error
Passive limit of 127 and MSCAN08 has gone to Error Passive state.
–
Transmitter Error Passive: The Transmit Error Counter has exceeded the
Error Passive limit of 127 and MSCAN08 has gone to Error Passive state.
–
Bus Off: The Transmit Error Counter has exceeded 255 and MSCAN08 has
gone to Bus Off state.
C.5.1
Interrupt Acknowledge
Interrupts are directly associated with one or more status flags in either the MSCAN08 Receiver
Flag Register (CRFLG) or the MSCAN08 Transmitter Control Register (CTCR). Interrupts are
pending as long as one of the corresponding flags is set. The flags in above registers must be reset
within the interrupt handler in order to handshake the interrupt. The flags are reset through writing
a ‘1’ to the corresponding bit position. A flag can not be cleared if the respective condition still
prevails.
Caution: Bit manipulation instructions (BSET) shall not be used to clear interrupt flags.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-11
188
Freescale Semiconductor, Inc.
C.5.2
Interrupt Vectors
The MSCAN08 supports four interrupt vectors as shown in Table C-1. The vector addresses are
dependent on the chip integration and to be defined. The relative interrupt priority is also
integration dependent and to be defined.
Freescale Semiconductor, Inc...
Table C-1 MSCAN08 Interrupt Vectors
Function
Source
Wake-Up
WUPIF
RWRNIF
TWRNIF
RERRIF
TERRIF
BOFFIF
OVRIF
RXF
TXE0
TXE1
TXE2
Error
Interrupts
Receive
Transmit
C.6
Local
Mask
WUPIE
RWRNIE
TWRNIE
RERRIE
TERRIE
BOFFIE
OVRIE
RXFIE
TXEIE0
TXEIE1
TXEIE2
Global
Mask
I Bit
Protocol Violation Protection
The MSCAN08 will protect the user from accidentally violating the CAN protocol through
programming errors. The protection logic implements the following features:
•
The receive and transmit error counters can not be written or otherwise manipulated.
•
All registers which control the configuration of the MSCAN08 can not be modified while the
MSCAN08 is on-line. The SFTRES bit in the MSCAN08 Module Control Register (see
Section C.12.2) serves as a lock to protect the following registers:
•
–
MSCAN08 Module Control Register 1 (CMCR1)
–
MSCAN08 Bus Timing Register 0 and 1 (CBTR0, CBTR1)
–
MSCAN08 Identifier Acceptance Control Register (CIDAC)
–
MSCAN08 Identifier Acceptance Registers (CIDAR0-3)
–
MSCAN08 Identifier Mask Registers (CIDMR0-3)
The TxCAN pin is forced to Recessive if the CPU goes into STOP mode.
C
TPG
MOTOROLA
C-12
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
189
Freescale Semiconductor, Inc.
C.7
Low Power Modes
Freescale Semiconductor, Inc...
The MSCAN08 has three modes with reduced power consumption compared to Normal Mode. In
Sleep and Soft Reset Mode, power consumption is reduced by stopping all clocks except those to
access the registers. In Power Down Mode, all clocks are stopped and no power is consumed.
The WAIT and STOP instruction put the MCU in low power consumption stand-by mode.Table C-2
summarizes the combinations of MSCAN08 and CPU modes. A particular combination of modes
is entered for the given settings of the bits SLPAK and SFTRES. For all modes, an MSCAN08
wake-up interrupt can occur only if SLPAK=WUPIE=1. While the CPU is in Wait Mode, the
MSCAN08 is operated as in Normal Mode.
Table C-2 MSCAN08 vs. CPU operating modes
MSCAN Mode
Power Down
Sleep
Soft Reset
Normal
CPU Mode
STOP
WAIT or RUN
(1)
SLPAK = X
SFTRES = X
SLPAK = 1
SFTRES = 0
SLPAK = 0
SFTRES = 1
SLPAK = 0
SFTRES = 0
(1) ÔXÕ means donÕt care.
C.7.1
MSCAN08 Internal Sleep Mode
The CPU can request the MSCAN08 to enter this low-power mode by asserting the SLPRQ bit in
the Module Configuration Register (see Figure C-6). The time when the MSCAN08 will then enter
Sleep Mode depends on its current activity:
•
if it is transmitting, it will continue to transmit until there is no more message to be transmitted,
and then go into Sleep Mode
•
if it is receiving, it will wait for the end of this message and then go into Sleep Mode
•
if it is neither transmitting nor receiving, it will immediately go into Sleep Mode
The application software must avoid to set up a transmission (by clearing one or more TXE flag(s))
and immediately request Sleep Mode (by setting SLPRQ). It will then depend on the exact
sequence of operations whether the MSCAN08 will start transmitting or go into Sleep Mode
directly.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-13
190
Freescale Semiconductor, Inc.
During Sleep Mode, the SLPAK flag is set. The application software should use this flag as a
handshake indication for the request to go into Sleep Mode. When in Sleep Mode, the MSCAN08
stops its own clocks and the TxCAN pin will stay in recessive state.
Freescale Semiconductor, Inc...
The MSCAN08 will leave Sleep Mode (wake-up) when
•
bus activity occurs or
•
the MCU clears the SLPRQ bit.
Note:
The MCU can not clear the SLPRQ bit before the MSCAN08 is in Sleep Mode
(SLPAK=1).
MSCAN08 Running
SLPRQ = 0
SLPAK = 0
MCU
MCU
or MSCAN08
MSCAN08 Sleeping
Sleep Request
SLPRQ = 1
SLPAK = 1
SLPRQ = 1
SLPAK = 0
MSCAN08
Figure C-6 Sleep Request / Acknowledge Cycle
C
TPG
MOTOROLA
C-14
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
191
Freescale Semiconductor, Inc.
C.7.2
MSCAN08 Soft Reset Mode
In Soft Reset Mode, the MSCAN08 is stopped. Registers can still be accessed. This mode is used
to initialize the module configuration, bit timing, and the CAN message filter. See Section C.12.2
for a complete description of the Soft Reset Mode.
Freescale Semiconductor, Inc...
C.7.3
MSCAN08 Power Down Mode
The MSCAN08 is in Power Down Mode when the CPU is in Stop Mode.
When entering the Power Down Mode, the MSCAN08 immediately stops all ongoing transmissions
and receptions, potentially causing CAN protocol violations. The user is responsible to take care
that the MSCAN08 is not active when Power Down Mode is entered. The recommended procedure
is to bring the MSCAN08 into Sleep Mode before the STOP instruction is executed.
To protect the CAN bus system from fatal consequences of violations to above rule, the MSCAN08
will drive the TxCAN pin into recessive state.
C.7.4
CPU Wait Mode
The MSCAN08 module remains active during CPU wait mode. The MSCAN08 will stay
synchronized to the CAN bus and will generate enabled transmit, receive and error interrupts to
the CPU. Any such interrupt will bring the MCU out of wait mode.
C.7.5
Programmable Wake-Up Function
The MSCAN08 can be programmed to apply a low-pass filter function to the RxCAN input line
while in internal Sleep Mode (see control bit WUPM in the Module Control Register,
Section C.12.2). This feature can be used to protect the MSCAN08 from wake-up due to short
glitches on the CAN bus lines. Such glitches can result from electromagnetic inference within noisy
environments.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-15
192
Freescale Semiconductor, Inc.
C.8
Timer Link
Freescale Semiconductor, Inc...
The MSCAN08 will generate a timer signal whenever a valid frame has been received. Because
the CAN specification defines a frame to be valid if no errors occurred before the EOF field has
been transmitted successfully, the timer signal will be generated right after the EOF. A pulse of one
bit time is generated. As the MSCAN08 receiver engine receives also the frames being sent by
itself, a timer signal will also be generated after a successful transmission.
C
The previously described timer signal can be routed into the on-chip Timer Interface Module (TIM).
Under the control of the Timer Link Enable (TLNKEN) bit in the CMCR0 will this signal be
connected to the Timer n Channel m input†.
After Timer n has been programmed to capture rising edge events it can be used to generate 16-bit
time stamps which can be stored under software control with the received message.
C.9
Clock System
Figure C-7 shows the structure of the MSCAN08 clock generation circuitry and its interaction with
the Clock Generation Module (CGM). With this flexible clocking scheme the MSCAN08 is able to
handle CAN bus rates ranging from 10 kbps up to 1 Mbps.
†
The timer channel being used for the timer link is integration dependent.
TPG
MOTOROLA
C-16
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
193
Freescale Semiconductor, Inc.
OSC
CGMXCLK
/2
CGMOUT
(to SIM)
Freescale Semiconductor, Inc...
BCS
PLL
/2
CGM
MSCAN08
(2 * Bus Freq.)
/2
MSCANCLK
CLKSRC
Prescaler
(1 .. 64)
time quanta clock
Figure C-7 Clocking Scheme
The Clock Source Flag (CLKSRC) in the MSCAN08 Module Control Register (CMCR1) (see
Section C.12.3) defines whether the MSCAN08 is connected to the output of the crystal oscillator
or to the Clock Generator Module output.
A programmable prescaler is used to generate from the MSCAN08 clock the time quanta (Tq)
clock. A time quantum is the atomic unit of time handled by the MSCAN08. A bit time is subdivided
into three segments†:
•
SYNC_SEG: This segment has a fixed length of one time quantum. Signal edges are expected
to happen within this section.
•
Time segment 1: This segment includes the PROP_SEG and the PHASE_SEG1 of the CAN
standard. It can be programmed by setting the parameter TSEG1 to consist of 4 to 16 time
quanta.
•
Time segment 2: This segment represents the PHASE_SEG2 of the CAN standard. It can be
programmed by setting the TSEG2 parameter to be 2 to 8 time quanta long.
The Synchronization Jump Width can be programmed in a range of 1 to 4 time quanta by setting
the SJW parameter.
Above parameters can be set by programming the Bus Timing Registers (CBTR0-1, see
Section C.12.4 and Section C.12.5).
†
For further explanation of the under-lying concepts please refer to ISO/DIS 11519-1, Section
10.3.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-17
194
Freescale Semiconductor, Inc.
It is the user’s responsibility to make sure that his bit time settings are in compliance with the CAN
standard. Figure C-8 and Table C-3 give an overview on the CAN conforming segment settings
and the related parameter values.
Freescale Semiconductor, Inc...
NRZ Signal
SYNC
_SEG
Time segment 1
(PROP_SEG + PHASE_SEG1)
Time Segment 2
(PHASE_SEG2)
1
4 ... 16
2 ... 8
8... 25 Time Quanta
= 1 Bit Time
Transmit point
Sample point
(single or triple sampling)
Figure C-8 Segments within the Bit Time
Table C-3 CAN Standard Compliant Bit Time Segment Settings
Time Segment 1
TSEG1
Time Segment 2
TSEG2
5 .. 10
4 .. 11
5 .. 12
6 .. 13
7 .. 14
8 .. 15
9 .. 16
4 .. 9
3 .. 10
4 .. 11
5 .. 12
6 .. 13
7 .. 14
8 .. 15
2
3
4
5
6
7
8
1
2
3
4
5
6
7
Synchronisation Jump
Width
1 .. 2
1 .. 3
1 .. 4
1 .. 4
1 .. 4
1 .. 4
1 .. 4
SJW
0 .. 1
0 .. 2
0 .. 3
0 .. 3
0 .. 3
0 .. 3
0 .. 3
C
TPG
MOTOROLA
C-18
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
195
Freescale Semiconductor, Inc.
C.10
Memory Map
The MSCAN08 occupies 128 Bytes in the CPU08 memory space. The absolute mapping is
implementation dependent with the base address being a multiple of 128. The background receive
buffer can only be read in test mode.
Freescale Semiconductor, Inc...
Table C-4 MSCAN08 Memory Map
$xx00
$xx08
$xx09
$xx0D
$xx0E
$xx0F
$xx10
$xx17
$xx18
$xx3F
$xx40
$xx4F
$xx50
$xx5F
$xx60
$xx6F
$xx70
$xx7F
CONTROL REGISTERS
9 BYTES
RESERVED
5 BYTES
ERROR COUNTERS
2 BYTES
IDENTIFIER FILTER
8 BYTES
RESERVED
40 BYTES
RECEIVE BUFFER
TRANSMIT BUFFER 0
TRANSMIT BUFFER 1
TRANSMIT BUFFER 2
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-19
196
Freescale Semiconductor, Inc.
C.11
Programmer’s Model of message storage
Freescale Semiconductor, Inc...
The following section details the organisation of the receive and transmit message buffers and the
associated control registers. For reasons of programmer interface simplification the receive and
transmit message buffers have the same outline. Each message buffer allocates 16 byte in the
memory map containing a 13 byte data structure. An additional Transmit Buffer Priority Register
(TBPR) is defined for the transmit buffers.
Table C-5 Message Buffer Organisation
Address
xxb0
xxb1
xxb2
xxb3
xxb4
xxb5
xxb6
xxb7
xxb8
xxb9
xxbA
xxbB
xxbC
xxbD
xxbE
xxbF
(1)
C.11.1
Register Name
Identifier Register 0
Identifier Register 1
Identifier Register 2
Identifier Register 3
Data Segment Register 0
Data Segment Register 1
Data Segment Register 2
Data Segment Register 3
Data Segment Register 4
Data Segment Register 5
Data Segment Register 6
Data Segment Register 7
Data Length Register
Transmit Buffer Priority Register(1)
unused
unused
Not Applicable for Receive Buffers
Message Buffer Outline
Figure C-9 shows the common 13 byte data structure of receive and transmit buffers for extended
identifiers. The mapping of standard identifiers into the IDR registers is shown in Figure C-10. All
bits of the 13 byte data structure are undefined out of reset.
C
TPG
MOTOROLA
C-20
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
197
Freescale Semiconductor, Inc.
C.11.2
Identifier Registers (IDRn)
The identifiers consist of either 11 bits (ID10 – ID0) for the standard, or 29 bits (ID28 - ID0) for the
extended format. ID10/28 is the most significant bit and is transmitted first on the bus during the
arbitration procedure. The priority of an identifier is defined to be highest for the smallest binary
number.
Register
Freescale Semiconductor, Inc...
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
IdentiÞer register 0 (IDR0)
Address bit 7
$xxb0
ID28
ID27
ID26
ID25
ID24
ID23
ID22
ID21
IdentiÞer register 1 (IDR1)
$xxb1
ID20
ID19
ID18
ID17
ID16
ID15
IdentiÞer register 2 (IDR2)
$xxb2
ID14
ID13
ID12
ID9
ID8
ID7
SRR(1) IDE(1)
ID11
ID10
IdentiÞer register 3 (IDR3)
$xxb3
ID6
ID5
ID4
ID3
ID2
ID1
ID0
RTR
Data segment register 0 (DSR0)
$xxb4
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Data segment register 1 (DSR1)
$xxb5
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Data segment register 2 (DSR2)
$xxb6
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Data segment register 3 (DSR3)
$xxb7
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Data segment register 4 (DSR4)
$xxb8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Data segment register 5 (DSR5)
$xxb9
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Data segment register 6 (DSR6)
$xxbA
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Data segment register 7 (DSR7)
$xxbB
DB7
DB6
DB5
DB4
Data length register (DLR)
$xxbC
DB3
DB2
DB1
DB0
DLC3
DLC2
DLC1
DLC0
Figure C-9 Receive/transmit message buffer extended identifier registers
SRR - Substitute Remote Request
This fixed recessive bit is used only in extended format. It must be set to 1 by the user for
transmission buffers and will be stored as received on the CAN bus for receive buffers
IDE — ID Extended
This flag indicates whether the extended or standard identifier format is applied in this buffer. In
case of a receive buffer the flag is set as being received and indicates to the CPU how to process
the buffer identifier registers. In case of a transmit buffer the flag indicates to the MSCAN08 what
type of identifier to send.
1 (set)
–
Extended format (29 bit)
0 (clear) –
Standard format (11 bit)
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-21
198
Freescale Semiconductor, Inc.
RTR — Remote transmission request
This flag reflects the status of the Remote Transmission Request bit in the CAN frame. In case of
a receive buffer it indicates the status of the received frame and allows to support the transmission
of an answering frame in software. In case of a transmit buffer this flag defines the setting of the
RTR bit to be sent.
1 (set)
–
Freescale Semiconductor, Inc...
0 (clear) –
Remote frame
Data frame
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
IdentiÞer register 0 (IDR0)
Register
Address bit 7
$xxb0
ID10
ID9
ID8
ID7
ID6
ID5
ID4
ID3
IdentiÞer register 1 (IDR1)
$xxb1
ID2
ID1
ID0
RTR
IDE(0)
IdentiÞer register 2 (IDR2)
$xxb2
IdentiÞer register 3 (IDR3)
$xxb3
Figure C-10 Standard identifier mapping registers
C.11.3
Data Length Register (DLR)
This register keeps the data length field of the CAN frame.
DLC3 – DLC0 — Data length code bits
The data length code contains the number of bytes (data byte count) of the respective message.
At transmission of a remote frame, the data length code is transmitted as programmed while the
number of transmitted bytes is always 0. The data byte count ranges from 0 to 8 for a data frame.
Table C-6 shows the effect of setting the DLC bits.
Table C-6 Data length codes
DLC3
0
0
0
0
0
0
0
0
1
C
Data length code
DLC2
DLC1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
0
0
DLC0
0
1
0
1
0
1
0
1
0
Data byte
count
0
1
2
3
4
5
6
7
8
TPG
MOTOROLA
C-22
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
199
Freescale Semiconductor, Inc.
C.11.4
Data Segment Registers (DSRn)
The eight data segment registers contain the data to be transmitted or being received. The number
of bytes to be transmitted or being received is determined by the data length code in the
corresponding DLR.
Freescale Semiconductor, Inc...
C.11.5
Transmit Buffer Priority Registers (TBPR)
Address bit 7
Transmit buffer priority reg. (TBPR)
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$xxbD PRIO7 PRIO6 PRIO5 PRIO4 PRIO3 PRIO2 PRIO1 PRIO0 UndeÞned
PRIO7 - PRIO0— Local Priority
This field defines the local priority of the associated message buffer. The local priority is used for
the internal priorisation process of the MSCAN08 and is defined to be highest for the smallest
binary number. The MSCAN08 implements the following internal priorisation mechanism:
•
All transmission buffers with a cleared TXE flag participate in the priorisation right before the
SOF (Start of Frame) is sent.
•
The transmission buffer with the lowest local priority field wins the priorisation.
•
In case of more than one buffer having the same lowest priority the message buffer with the
lower index number wins.
Caution: To ensure data integrity, no registers of the transmit buffers shall be written while the
associated TXE flag is cleared.
Caution: To ensure data integrity, no registers of the receive buffer shall be read while the RXF
flag is cleared.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-23
200
Freescale Semiconductor, Inc.
C.12
Programmer’s Model of Control Registers
C.12.1
Overview
Freescale Semiconductor, Inc...
The programmer’s model has been laid out for maximum simplicity and efficiency. Table C-7 gives
an overview on the control register block of the MSCAN08:
Table C-7 MSCAN08 Control register structure
Register
Address
bit 7
bit 6
bit 5
CMCR0
$xx00
0
0
0
bit 4
bit 3
bit 2
CMCR1*
$xx01
0
0
0
0
0
LOOPB
CBTR0*
$0002
SJW1
SJW0
BRP5
BRP4
BRP3
BRP2
CBTR1*
$xx03
SAMP
CRFLG
$xx04
WUPIF RWRNIF TWRNIF RERRIF TERRIF BOFFIF
OVRIF
RXF
CRIER
$xx05
WUPIE RWRNIE TWRNIE RERRIE TERRIE BOFFIE
CTFLG
$xx06
SYNCH TLNKEN SLPAK
bit 1
bit 0
SLPRQ SFTRES
WUPM CLKSRC
BRP1
BRP0
TSEG22 TSEG21 TSEG20 TSEG13 TSEG12 TSEG11 TSEG10
0
ABTAK2 ABTAK1 ABTAK0
ABTRQ2 ABTRQ1 ABTRQ0
OVRIE
RXFIE
0
TXE2
TXE1
TXE0
0
TXEIE2
TXEIE1
TXEIE0
0
0
IDHIT1
IDHIT0
CTCR
$xx07
0
CIDAC*
$xx08
0
Reserved
$xx09$xx0D
CRXERR
$xx0E
RXERR7 RXERR6 RXERR5 RXERR4 RXERR3 RXERR2 RXERR1 RXERR0
CTXERR
$xx0F
TXERR7 TXERR6 TXERR5 TXERR4 TXERR3 TXERR2 TXERR1 TXERR0
CIDAR0*
$xx10
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDAR1*
$xx11
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDAR2*
$xx12
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDAR3*
$xx13
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDMRO*
$xx14
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDMR1*
$xx15
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDMR2*
$xx16
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDMR3*
$xx17
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
0
IDAM1
IDAM0
*. Writeable only when SFTRES is set.
C
TPG
MOTOROLA
C-24
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
201
Freescale Semiconductor, Inc.
C.12.2
MSCAN08 Module Control Register (CMCR0).
Address bit 7
Module control reg. 0 (CMCR0)
$xx00
0
bit 6
bit 5
0
0
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
SYNCH TLNKEN SLPAK SLPRQ SFTRES 0000 0001
Freescale Semiconductor, Inc...
SYNCH — Synchronized Status
This bit indicates whether the MSCAN08 is synchronized to the CAN bus and as such can
participate in the communication process.
1 (set)
–
0 (clear) –
MSCAN08 is synchronized to the CAN bus
MSCAN08 is not synchronized to the CAN bus
TLNKEN - Timer Enable
This flag is used to establish a link between the MSCAN08 and the on-chip timer (see Section C.8).
1 (set)
–
0 (clear) –
The MSCAN08 timer signal output is connected to the timer.
No connection.
SLPAK — Sleep Mode Acknowledge
This flag indicates whether the MSCAN08 is in module internal sleep mode. It shall be used as a
handshake for the sleep mode request (see Section C.7.1).
1 (set)
–
Sleep – The MSCAN08 is in internal sleep mode.
0 (clear) –
Wake-up – The MSCAN08 will function normally.
SLPRQ — Sleep request, Go to internal sleep mode
This flag allows to request the MSCAN08 to go into an internal power-saving mode (see
Section C.7.1).
1 (set)
–
0 (clear) –
Sleep – The MSCAN08 will go into internal sleep mode.
Wake-up – The MSCAN08 will function normally.
SFTRES— Soft Reset
When this bit is set by the CPU, the MSCAN08 immediately enters the soft reset state. Any
ongoing transmission or reception is aborted and synchronisation to the bus is lost.
The following registers will go into and stay in the same state as out of hard reset: CMCR0,
CRFLG, CRIER, CTFLG, CTCR.
The registers CMCR1, CBTR0, CBTR1, CIDAC, CIDAR0-3, CIDMR0-3 can only be written by the
CPU when the MSCAN08 is in soft reset state. The values of the error counters are not affected
by soft reset.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-25
202
Freescale Semiconductor, Inc.
When this bit is cleared by the CPU, the MSCAN08 will try to synchronize to the CAN bus: If the
MSCAN08 is not in bus-off state it will be synchronized after 11 recessive bits on the bus; if the
MSCAN08 is in bus-off state it continues to wait for 128 occurrences of 11 recessive bits.
Clearing SFTRES and writing to other bits in CMCR0 must be in separate instructions.
1 (set)
–
Freescale Semiconductor, Inc...
0 (clear) –
C.12.3
MSCAN08 in soft reset state.
Normal operation
MSCAN08 Module Control Register (CMCR1)
Address bit 7
Module control reg. 1 (CMCR1)
$xx01
0
bit 6
bit 5
bit 4
bit 3
0
0
0
0
bit 2
bit 1
bit 0
State
on reset
LOOPB WUPM CLKSRC 0000 0000
LOOPB - Loop Back Self Test Mode
When this bit is set the MSCAN08 performs an internal loop back which can be used for self test
operation: the bit stream output of the transmitter is fed back to the receiver. The RxCAN input pin
is ignored and the TxCAN output goes to the recessive state (1). Note that in this state the
MSCAN08 ignores the ACK bit to insure proper reception of its own message and will treat
messages being received while in transmission as received messages from remote nodes.
1 (set)
–
0 (clear) –
Activate loop back self test mode
Normal operation
WUPM - Wake-Up Mode
This flag defines whether the integrated low-pass filter is applied to protect the MSCAN08 from
spurious wake-ups (see Section C.7.5).
1 (set)
–
0 (clear) –
MSCAN08 will wake up the CPU only in case of dominant pulse on
the bus which has a length of at least approximately Twup.
MSCAN08 will wake up the CPU after any recessive to dominant
edge on the CAN bus.
CLKSRC - Clock Source
This flag defines which clock source the MSCAN08 module is driven from (see Section C.9).
1 (set)
–
0 (clear) –
Note:
C
THE MSCAN08 clock source is CGMOUT (see Figure C-7).
The MSCAN08 clock source is CGMXCLK/2 (see Figure C-7).
The CMCR1 register can only be written if the SFTRES bit in the MSCAN08 Module
Control Register is set
TPG
MOTOROLA
C-26
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
203
Freescale Semiconductor, Inc.
C.12.4
MSCAN08 Bus Timing Register 0 (CBTR0)
Address bit 7
Bus timing reg. 0 (CBTR0)
Sxx02
bit 6
State
on reset
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
SJW1 SJW0 BRP5
BRP4
BRP3
BRP2
BRP1
BRP0 0000 0000
Freescale Semiconductor, Inc...
SJW1, SJW0 — Synchronization Jump Width
The synchronization jump width defines the maximum number of time quanta (Tq) clock cycles by
which a bit may be shortened, or lengthened, to achieve resynchronization on data transitions on
the bus (see Table C-8).
Table C-8 Synchronization jump width
SJW1
SJW0
Synchronization jump width
0
0
1
1
0
1
0
1
1 Tq clock cycle
2 Tq clock cycles
3 Tq clock cycles
4 Tq clock cycles
BRP5 – BRP0 — Baud Rate Prescaler
These bits determine the time quanta (Tq) clock, which is used to build up the individual bit timing,
according to Table C-9.
Table C-9 Baud rate prescaler
Note:
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0
0
0
0
0
:
:
1
0
0
0
0
:
:
1
0
0
0
0
:
:
1
0
0
0
0
:
:
1
0
0
1
1
:
:
1
0
1
0
1
:
:
1
Prescaler
value (P)
1
2
3
4
:
:
64
The CBTR0 register can only be written if the SFTRES bit in the MSCAN08 Module
Control Register is set.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-27
204
Freescale Semiconductor, Inc.
C.12.5
MSCAN08 Bus Timing Register 1 (CBTR1)
Address bit 7
Bus timing reg. 1 (CBTR1)
$xx03
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
SAMP TSEG22TSEG21TSEG20TSEG13TSEG12TSEG11TSEG10 0000 0000
Freescale Semiconductor, Inc...
SAMP — Sampling
This bit determines the number of samples of the serial bus to be taken per bit time. If set three
samples per bit are taken, the regular one (sample point) and two preceding samples, using a
majority rule. For higher bit rates SAMP should be cleared, which means that only one sample will
be taken per bit.
1 (set)
–
0 (clear) –
Three samples per bit.
One sample per bit.
TSEG22 – TSEG10 — Time Segment
Time segments within the bit time fix the number of clock cycles per bit time, and the location of
the sample point.
Table C-10 Time segment syntax
SYNC_SEG
Transmit point
Sample point
System expects transitions to occur on the bus during this
period.
A node in transmit mode will transfer a new value to the
CAN bus at this point.
A node in receive mode will sample the bus at this point. If
the three samples per bit option is selected then this point
marks the position of the third sample.
Time segment 1 (TSEG1) and time segment 2 (TSEG2) are programmable as shown in
Table C-11
The bit time is determined by the oscillator frequency, the baud rate prescaler, and the number of
time quanta (Tq) clock cycles per bit (as shown in Table C-11).
Note:
The CBTR1 register can only be written if the SFTRES bit in the MSCAN08 Module
Control Register is set
C
TPG
MOTOROLA
C-28
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
205
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Table C-11 Time segment values
TSEG TSEG TSEG TSEG
Time segment 1
13
12
11
10
0
0
0
0
1 Tq clock cycle
0
0
0
1
2 Tq clock cycles
0
0
1
0
3 Tq clock cycles
0
0
1
1
4 Tq clock cycles
.
.
.
.
.
.
.
.
.
.
1
1
1
1
16 Tq clock cycles
C.12.6
TSEG TSEG TSEG
22
21
20
0
0
0
0
0
1
.
.
.
.
.
.
1
1
1
Time segment 2
1 Tq clock cycle
2 Tq clock cycles
.
.
8 Tq clock cycles
MSCAN08 Receiver Flag Register (CRFLG)
Address bit 7
Receiver ßag register (CRFLG)
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
$xx04 WUPIF RWRNIFTWRNIFRERRIF TERRIF BOFFIF OVRIF
bit 0
State
on reset
RXF
0000 0000
All bits of this register are read and clear only. A flag can be cleared by writing a 1 to the
corresponding bit position. A flag can only be cleared when the condition which caused the setting
is no more valid. Writing a 0 has no effect on the flag setting. Every flag has an associated interrupt
enable flag in the CRIER register. A hard or soft reset will clear the register.
WUPIF — Wake-up Interrupt Flag
If the MSCAN08 detects bus activity whilst it is asleep, it clears the SLPAK bit in the CMCR0
register; the WUPIF bit will then be set. If not masked, a Wake-Up interrupt is pending while this
flag is set.
1 (set)
–
0 (clear) –
MSCAN08 has detected activity on the bus and requested wake-up.
No wake-up activity has been observed while in sleep mode.
RWRNIF — Receiver Warning Interrupt Flag
This bit will be set when the MSCAN08 went into warning status due to the Receive Error counter
being in the range of 96 to 127. If not masked, an Error interrupt is pending while this flag is set.
1 (set)
–
0 (clear) –
MSCAN08 went into receiver warning status.
No receiver warning status has been reached.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-29
206
Freescale Semiconductor, Inc.
TWRNIF — Transmitter Warning Interrupt Flag
This bit will be set when the MSCAN08 went into warning status due to the Transmit Error counter
being in the range of 96 to 127. If not masked, an Error interrupt is pending while this flag is set.
1 (set)
–
0 (clear) –
MSCAN08 went into transmitter warning status.
No transmitter warning status has been reached.
Freescale Semiconductor, Inc...
RERRIF — Receiver Error Passive Interrupt Flag
This bit will be set when the MSCAN08 went into error passive status due to the Receive Error
counter exceeded 127. If not masked, an Error interrupt is pending while this flag is set.
1 (set)
–
0 (clear) –
MSCAN08 went into receiver error passive status.
No receiver error passive status has been reached.
TERRIF — Transmitter Error Passive Interrupt Flag
This bit will be set when the MSCAN08 went into error passive status due to the Transmit Error
counter exceeded 127. If not masked, an Error interrupt is pending while this flag is set.
1 (set)
–
0 (clear) –
MSCAN08 went into transmitter error passive status.
No transmitter error passive status has been reached.
BOFFIF — Bus-Off Interrupt Flag
This bit will be set when the MSCAN08 went into bus-off status, due to the Transmit Error counter
exceeded 255. If not masked, an Error interrupt is pending while this flag is set.
1 (set)
–
0 (clear) –
MSCAN08 went into bus-off status.
No bus-off status has been reached.
OVRIF — Overrun Interrupt Flag
This bit will be set when a data overrun condition occurred. If not masked, an Error interrupt is
pending while this flag is set.
1 (set)
–
0 (clear) –
A data overrun has been detected.
No data overrun has occurred.
C
TPG
MOTOROLA
C-30
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
207
Freescale Semiconductor, Inc.
RXF — Receive Buffer Full
Freescale Semiconductor, Inc...
The RXF flag is set by the MSCAN08 when a new message is available in the foreground receive
buffer. This flag indicates whether the buffer is loaded with a correctly received message. After the
CPU has read that message from the receive buffer the RXF flag must be handshaked to release
the buffer. A set RXF flag prohibits the exchange of the background receive buffer into the
foreground buffer. In that case the MSCAN08 will signal an overload condition. If not masked, a
Receive interrupt is pending while this flag is set.
1 (set)
–
0 (clear) –
Note:
The receive buffer is full. A new message is available.
The receive buffer is released (not full).
The CRFLG register is held in the reset state when the SFTRES bit in CMCR0 is set.
C.12.7
MSCAN08 Receiver Interrupt Enable Register (CRIER)
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Receiver interrupt enable reg. (CRIER) $xx05 WUPIE RWRNIETWRNIE RERRIE TERRIE BOFFIE OVRIE RFXIE 0000 0000
WUPIE — Wake-up Interrupt Enable
1 (set)
–
0 (clear) –
A wake-up event will result in a wake-up interrupt.
No interrupt will be generated from this event.
RWRNIE — Receiver Warning Interrupt Enable
1 (set)
–
0 (clear) –
A receiver warning status event will result in an error interrupt.
No interrupt will be generated from this event.
TWRNIE — Transmitter Warning Interrupt Enable
1 (set)
–
0 (clear) –
A transmitter warning status event will result in an error interrupt.
No interrupt will be generated from this event.
RERRIE — Receiver Error Passive Interrupt Enable
1 (set)
–
0 (clear) –
A receiver error passive status event will result in an error interrupt.
No interrupt will be generated from this event.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-31
208
Freescale Semiconductor, Inc.
TERRIE — Transmitter Error Passive Interrupt Enable
1 (set)
–
0 (clear) –
A transmitter error passive status event will result in an error interrupt.
No interrupt will be generated from this event.
BOFFIE — Bus-Off Interrupt Enable
Freescale Semiconductor, Inc...
1 (set)
–
A bus-off event will result in an error interrupt.
0 (clear) –
No interrupt will be generated from this event.
OVRIE — Overrun Interrupt Enable
1 (set)
–
0 (clear) –
An overrun event will result in an error interrupt.
No interrupt will be generated from this event.
RXFIE — Receiver Full Interrupt Enable
1 (set)
–
0 (clear) –
Note:
A receive buffer full (successful message reception) event will result
in a receive interrupt.
No interrupt will be generated from this event.
The CRIER register is held in the reset state when the SFTRES bit in CMCR0 is set.
C
TPG
MOTOROLA
C-32
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
209
Freescale Semiconductor, Inc.
C.12.8
MSCAN08 Transmitter Flag Register (CTFLG)
Address bit 7
Freescale Semiconductor, Inc...
Transmitter ßag reg. (CTFLG)
$xx06
0
bit 6
bit 5
bit 4
ABTAK2 ABTAK1 ABTAK0
State
on reset
bit 3
bit 2
bit 1
bit 0
0
TXE2
TXE1
TXE0 0000 0111
All bits of this register are read and clear only. A flag can be cleared by writing a 1 to the
corresponding bit position. Writing a 0 has no effect on the flag setting. Every flag has an
associated interrupt enable flag in the CTCR register. A hard or soft reset will clear the register.
ABTAK2 - ABTAK0 — Abort Acknowledge
This flag acknowledges that a message has been aborted due to a pending abort request from the
CPU. After a particular message buffer has been flagged empty, this flag can be used by the
application software to identify whether the message has been aborted successfully or has been
sent in the meantime. The flag is reset implicitly whenever the associated TXE flag is set to 0.
1 (set)
–
0 (clear) –
The message has been aborted.
The massage has not been aborted, thus has been sent out.
TXE2 - TXE0 —Transmitter Buffer Empty
This flag indicates that the associated transmit message buffer is empty, thus not scheduled for
transmission. The CPU must handshake (clear) the flag after a message has been set up in the
transmit buffer and is due for transmission. The MSCAN08 will set the flag after the message has
been sent successfully. The flag will also be set by the MSCAN08 when the transmission request
was successfully aborted due to a pending abort request (Section C.12.9). If not masked, a
Transmit interrupt is pending while this flag is set.
A reset of this flag will also reset the Abort Acknowledge (ABTAK, see above) and the Abort
Request (ABTRQ, see Section C.12.9) flags of the particular buffer.
1 (set)
–
0 (clear) –
Note:
The associated message buffer is empty (not scheduled).
The associated message buffer is full (loaded with a message due for
transmission).
The CTFLG register is held in the reset state when te SFTRES bit in CMCR0 is set.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-33
210
Freescale Semiconductor, Inc.
C.12.9
MSCAN08 Transmitter Control Register (CTCR)
Address bit 7
Transmitter control reg. (CTCR)
$xx07
0
bit 6
bit 5
bit 4
ABTRQ2ABTRQ1ABTRQ0
bit 3
0
bit 2
bit 1
bit 0
State
on reset
TXEIE2 TXEIE1 TXEIE0 0000 0000
Freescale Semiconductor, Inc...
ABTRQ2 - ABTRQ0 — Abort Request
The CPU sets this bit to request that an already scheduled message buffer (TXE = 0) shall be
aborted. The MSCAN08 will grant the request when the message is not already under
transmission. When a message is aborted the associated TXE and the Abort Acknowledge flag
(ABTAK, see Section C.12.8) will be set and an TXE interrupt will occur if enabled. The CPU can
not reset ABTRQx. ABTRQx is reset implicitly whenever the associated TXE flag is set.
1 (set)
–
0 (clear) –
Abort request pending.
No abort request.
TXEIE2 - TXEIE0 — Transmitter Empty Interrupt Enable
1 (set)
–
0 (clear) –
Note:
A transmitter empty (transmit buffer available for transmission) event
will result in a transmitter empty interrupt.
No interrupt will be generated from this event.
The CTCR register is held in the reset state when the SFTRES bit in CMCR0 is set.
C
TPG
MOTOROLA
C-34
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
211
Freescale Semiconductor, Inc.
C.12.10
MSCAN08 Identifier Acceptance Control Register (CIDAC)
Address bit 7
IdentiÞer acceptance control reg. (CIDAC) $xx08
0
bit 6
0
bit 5
bit 4
IDAM1 IDAM0
bit 3
bit 2
0
0
bit 1
bit 0
State
on reset
IDHIT1 IDHIT0 0000 0000
Freescale Semiconductor, Inc...
IDAM1- IDAM0— Identifier Acceptance Mode
The CPU sets these flags to define the identifier acceptance filter organisation (see Section C.4).
Table C-12 summarizes the different settings. In Filter Closed mode no messages will be accepted
such that the foreground buffer will never be reloaded.
Table C-12 Identifier Acceptance Mode Settings
IDAM1
0
0
1
1
IDAM0
0
1
0
1
Identifier Acceptance Mode
Single 32 bit Acceptance Filter
Two 16 bit Acceptance Filter
Four 8 bit Acceptance Filters
Filter Closed
IDHIT1- IDHIT0— Identifier Acceptance Hit Indicator
The MSCAN08 sets these flags to indicate an identifier acceptance hit (see Section C.4).
Table C-12 summarizes the different settings.
Table C-13 Identifier Acceptance Hit Indication
IDHIT1
0
0
1
1
IDHIT0
0
1
0
1
Identifier Acceptance Hit
Filter 0 Hit
Filter 1 Hit
Filter 2 Hit
Filter 3 Hit
The IDHIT indicators are always related to the message in the foreground buffer. When a message
gets copied from the background to the foreground buffer the indicators are updated as well.
Note:
The CIDAC register can only be written if the SFTRES bit in the MSCAN08 Module
Control Register is set.
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-35
212
Freescale Semiconductor, Inc.
C.12.11
MSCAN08 Receive Error Counter (CRXERR)
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Receive error counter (CRXERR) $xx0E RXERR7 RXERR6 RXERR5 RXERR4 RXERR3 RXERR2 RXERR1 RXERR00000 0000
Freescale Semiconductor, Inc...
This register reflects the status of the MSCAN08 receive error counter. The register is read only.
C.12.12
MSCAN08 Transmit Error Counter (CTXERR)
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Transmit error counter (CTXERR) $xx0F TXERR7 TXERR6 TXERR5 TXERR4 TXERR3 TXERR2 TXERR1 TXERR0 0000 0000
This register reflects the status of the MSCAN08 transmit error counter. The register is read only.
Note:
Both error counters may only be read when in Sleep or Soft Reset Mode..
C
TPG
MOTOROLA
C-36
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
213
Freescale Semiconductor, Inc.
C.12.13
MSCAN08 Identifier Acceptance Registers (CIDAR0-3)
Freescale Semiconductor, Inc...
On reception each message is written into the background receive buffer. The CPU is only
signalled to read the message however, if it passes the criteria in the identifier acceptance and
identifier mask registers (accepted); otherwise, the message will be overwritten by the next
message (dropped).
The acceptance registers of the MSCAN08 are applied on the IDR0 to IDR3 registers of incoming
messages in a bit by bit manner.
For extended identifiers all four acceptance and mask registers are applied. For standard
identifiers only the first two (IDAR0, IDAR1) are applied. In the latter case it is required to program
the mask register CIDMR1 in the three last bits (AC2 - AC0) to don’t care.
Register
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State on
reset
CIDAR0
$xx10
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
CIDAR1
$xx11
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
CIDAR2
$xx12
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
CIDAR3
$xx13
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
AC7 – AC0 — Acceptance Code Bits
AC7 – AC0 comprise a user defined sequence of bits with which the corresponding bits of the
related identifier register (IDRn) of the receive message buffer are compared. The result of this
comparison is then masked with the corresponding identifier mask register.
Note:
The CIDAR0-3 registers can only be written if the SFTRES bit in the MSCAN08 Module
Control Register is set
C
TPG
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN08)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
C-37
214
Freescale Semiconductor, Inc.
C.12.14
MSCAN08 Identifier Mask Registers (CIDMR0-3)
Freescale Semiconductor, Inc...
Register
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State on
reset
CIDMR0
$xx14
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
CIDMR1
$xx15
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
CIDMR2
$xx16
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
CIDMR3
$xx17
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
The identifier mask register specifies which of the corresponding bits in the identifier acceptance
register are relevant for acceptance filtering.
AM7 – AM0 — Acceptance Mask Bits
If a particular bit in this register is cleared this indicates that the corresponding bit in the identifier
acceptance register must be the same as its identifier bit, before a match will be detected. The
message will be accepted if all such bits match. If a bit is set, it indicates that the state of the
corresponding bit in the identifier acceptance register will not affect whether or not the message is
accepted.
1 (set)
–
0 (clear) –
Note:
Ignore corresponding acceptance code register bit.
Match corresponding acceptance code register and identifier bits.
The CIDMR0-3 registers can only be written if the SFTRES bit in the MSCAN08 Module
Control Register is set.
C
TPG
MOTOROLA
C-38
THE MOTOROLA SCALEABLE CAN (MSCAN08)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
215
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
D
THE MOTOROLA SCALEABLE CAN
(MSCAN12) MODULE
The MSCAN12 is the specific implementation of the Motorola Scalable CAN (MSCAN) concept
targeted for the Motorola M68HC12 Microcontroller Family.
The module is a communication controller implementing the CAN 2.0 A/B protocol as defined in
the BOSCH specification dated September 1991.
The CAN protocol was primarily, but not only, designed to be used as a vehicle serial data bus,
meeting the specific requirements of this field: real-time processing, reliable operation in the EMI
environment of a vehicle, cost-effectiveness and required bandwidth.
MSCAN12 utilises an advanced buffer arrangement resulting in a predictable real-time behaviour
and simplifies the application software.
D.1
Features
The basic features of the MSCAN12 are as follows:
•
Modular Architecture
•
Implementation of the CAN protocol - Version 2.0A/B
–
Standard and extended data frames.
–
0 - 8 bytes data length.
–
Programmable bit rate up to 1 Mbps†.
•
Support for Remote Frames.
•
Double buffered receive storage scheme.
•
Triple buffered transmit storage scheme with internal priorisation using a “local priority”
concept.
†
D
Depending on the actual bit timing and the clock jitter of the PLL.
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-1
216
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
•
Flexible maskable identifier filter supports alternatively two full size extended identifier filters or
four 16-bit filters or eight 8-bit filters.
•
Programmable wake-up functionality with integrated low-pass filter.
•
Programmable Loop-Back mode supports self-test operation.
•
Separate signalling and interrupt capabilities for all CAN receiver and transmitter error states
(Warning, Error Passive, Bus-Off).
•
Programmable MSCAN12 clock source either CPU bus clock or crystal oscillator output.
•
Programmable link to on-chip Timer Interface Module (TIM) for time-stamping and network
synchronisation.
•
Low power Sleep Mode.
D.2
External Pins
The MSCAN12 uses 2 external pins, 1 input (RxCAN) and 1 output (TxCAN). The TxCAN output
pin represents the logic level on the CAN: ‘0’ is for a dominant state, and ‘1’ is for a recessive state.
RxCAN is on bit 0 of Port CAN, TxCAN is on bit 1. The remaining six pins of Port CAN are
controlled by registers in the MSCAN12 address space (see Section D.12.15 through
Section D.12.17). (See the chapter on I/O ports of the specific MCU for the actual number of pins
used for Port CAN.)
A typical CAN system with MSCAN12 is shown in Figure D-1 below.
Each CAN station is connected physically to the CAN bus lines through a transceiver chip. The
transceiver is capable of driving the large current needed for the CAN and has current protection,
against defected CAN or defected stations.
D
MOTOROLA
D-2
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
217
Freescale Semiconductor, Inc.
CAN station 1
CAN node 1
CAN node 2
CAN node n
Freescale Semiconductor, Inc...
MCU
CAN Controller
(MSCAN12)
TxCAN
RxCAN
Transceiver
CAN_H
CAN_L
C A N - Bus
Figure D-1 The CAN System
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-3
218
Freescale Semiconductor, Inc.
D.3
Message Storage
MSCAN12 facilitates a sophisticated message storage system which addresses the requirements
of a broad range of network applications.
Freescale Semiconductor, Inc...
D.3.1
Background
Modern application layer software is built upon two fundamental assumptions:
1) Any CAN node is able to send out a stream of scheduled messages without
releasing the bus between two messages. Such nodes will arbitrate for the
bus right after sending the previous message and will only release the bus
in case of lost arbitration.
2) The internal message queue within any CAN node is organized such that if
more than one message is ready to be sent, the highest priority message will
be sent out first.
Above behaviour can not be achieved with a single transmit buffer. That buffer must be reloaded
right after the previous message has been sent. This loading process lasts a definite amount of
time and has to be completed within the Inter-Frame Sequence (IFS) in order to be able to send
an uninterrupted stream of messages. Even if this is feasible for limited CAN bus speeds it requires
that the CPU reacts with short latencies to the transmit interrupt.
A double buffer scheme would de-couple the re-loading of the transmit buffers from the actual
message sending and as such reduces the reactiveness requirements on the CPU. Problems may
arise if the sending of a message would be finished just while the CPU re-loads the second buffer,
no buffer would then be ready for transmission and the bus would be released.
At least three transmit buffers are required to meet the first of above requirements under all
circumstances. The MSCAN12 has three transmit buffers.
The second requirement calls for some sort of internal priorisation which the MSCAN12
implements with the “local priority” concept described below.
D
MOTOROLA
D-4
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
219
Freescale Semiconductor, Inc.
D.3.2
Receive Structures
Freescale Semiconductor, Inc...
The received messages are stored in a two stage input FIFO. The two message buffers are
alternately mapped into a single memory area (see Figure D-2). While the background receive
buffer (RxBG) is exclusively associated to the MSCAN12, the foreground receive buffer (RxFG) is
addressable by the CPU12. This scheme simplifies the handler software as only one address area
is applicable for the receive process.
Both buffers have a size of 13 bytes to store the CAN control bits, the identifier (standard or
extended) and the data contents (for details see Section D.11).
The Receiver Full flag (RXF) in the MSCAN12 Receiver Flag Register (CRFLG) (see
Section D.12.6) signals the status of the foreground receive buffer. When the buffer contains a
correctly received message with matching identifier this flag is set.
After the MSCAN12 has successfully received a message into the background buffer and if the
message passes the filter (for details see Section D.4) it copies the content of RxBG into RxFG†,
sets the RXF flag, and emits a receive interrupt to the CPU‡. A new message, which may follow
immediately after the IFS field of the CAN frame, will be received into RxBG. The over-writing of
the background buffer is independent of the identifier filter function The user’s receive handler has
to read the received message from RxFG and then reset the RXF flag in order to acknowledge the
interrupt and to release the foreground buffer
An overrun condition occurs when both, the foreground and the background receive message
buffers are filled with correctly received messages with accepted identifiers and a further message
is being received from the bus. The latter message will be discarded and an error interrupt with
overrun indication will occur if enabled. While in the overrun situation, the MSCAN12 will stay
synchronized to the CAN bus and is able to transmit messages but will discard all incoming
messages.
Note:
MSCAN12 will receive its own messages into the background receive buffer RxBG but
will NOT overwrite RxFG and will NOT emit a receive interrupt nor will it acknowledge
(ACK) its own messages on the CAN bus. The exception to this rule is that when in
loop-back mode MSCAN12 will treat its own messages exactly like all other incoming
messages.
D
†
Only if the RxF flag is not set.
‡
The receive interrupt will occur only if not masked. A polling scheme can be applied on RxF
also.
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-5
220
Freescale Semiconductor, Inc.
.
MSCAN12
CPU12 bus
RxBG
Freescale Semiconductor, Inc...
RxFG RXF
Tx0
TXE
PRIO
Tx1
TXE
PRIO
Tx2
TXE
PRIO
D
Figure D-2 User model for message buffer organisation
MOTOROLA
D-6
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
221
Freescale Semiconductor, Inc.
D.3.3
Transmit Structures
Freescale Semiconductor, Inc...
The MSCAN12 has a triple transmit buffer scheme in order to allow multiple messages to be set
up in advance and to achieve an optimized real-time performance. The three buffers are arranged
as shown in Figure D-2.
All three buffers have a 13 byte data structure similar to the outline of the receive buffers (see
Section D.11). An additional Transmit Buffer Priority Register (TBPR) contains an 8-bit so called
“Local Priority” field (PRIO) (see Section D.11.5).
In order to transmit a message, the CPU12 has to identify an available transmit buffer which is
indicated by a set Transmit Buffer Empty (TXE) Flags in the MSCAN12 Transmitter Flag Register
(CTFLG) (see Section D.12.8).
The CPU12 then stores the identifier, the control bits and the data content into one of the transmit
buffers. Finally, the buffer has to be flagged as being ready for transmission by clearing the TXE
flag.
The MSCAN12 will then schedule the message for transmission and will signal the successful
transmission of the buffer by setting the TXE flag. A transmit interrupt will be emitted† when TXE
is set and this can be used to drive the application software to re-load the buffer.
In case more than one buffer is scheduled for transmission when the CAN bus becomes available
for arbitration, the MSCAN12 uses the “local priority” setting of the three buffers for priorisation.
For this purpose every transmit buffer has an 8-bit local priority field (PRIO). The application
software sets this field when the message is set up. The local priority reflects the priority of this
particular message relative to the set of messages being emitted from this node. The lowest binary
value of the PRIO field is defined to be the highest priority.
The internal scheduling process takes place whenever the MSCAN12 arbitrates for the bus. This
is also the case after the occurrence of a transmission error.
When a high priority message is scheduled by the application software it may become necessary
to abort a lower priority message being set up in one of the three transmit buffers. As messages
that are already under transmission can not be aborted, the user has to request the abort by
setting the corresponding Abort Request Flag (ABTRQ) in the Transmission Control Register
(CTCR). The MSCAN12 then grants the request, if possible, by setting the corresponding Abort
Request Acknowledge (ABTAK) and the TXE flag in order to release the buffer and by emitting a
transmit interrupt. The transmit interrupt handler software can tell from the setting of the ABTAK
flag whether the message was aborted (ABTAK=1), or sent in the meantime (ABTAK=0).
D
†
The transmit interrupt will occur only if not masked. A polling scheme can be applied on TXE
also.
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-7
222
Freescale Semiconductor, Inc.
D.4
Identifier Acceptance Filter
Freescale Semiconductor, Inc...
A very flexible programmable generic identifier acceptance filter has been introduced in order to
reduce the CPU interrupt loading. The filter is programmable to operate in four different modes:
•
Two identifier acceptance filters, each to be applied to the full 29 bits of the identifier and to the
following bits of the CAN frame: RTR, IDE, SRR. This mode implements two filters for a full
length CAN 2.0B compliant extended identifier. Figure D-3 shows how the first 32-bit filter bank
(CIDAR0-3, CIDMR0-3) produces a filter 0 hit. Similarly, the second filter bank (CIDAR4-7,
CIDMR4-7) produces a filter 1 hit.
•
Four identifier acceptance filters, each to be applied to a) the 11 bits of the identifier and the
RTR bit of CAN 2.0A mesages or b) the 14 most significant bits of the identifier of CAN 2.0B
messages. Figure D-4 shows how the first 32-bit filter bank (CIDAR0-3, CIDMR0-3) produces
filter 0 and 1 hits. Similarly, the second filter bank (CIDAR4-7, CIDMR4-7) produces filter 2 and
3 hits.
•
Eight identifier acceptance filters, each to be applied to the first 8 bits of the identifier. This
mode implements eight independent filters for the first 8 bit of a CAN 2.0A compliant standard
identifier, or of a CAN 2.0B compliant extended identifier. Figure D-5 shows how the first 32-bit
filter bank (CIDAR0-3, CIDMR0-3) produces filter 0 to 3 hits. Similarly, the second filter bank
(CIDAR4-7, CIDMR4-7) produces filter 4 to 7 hits.
•
Closed filter. No CAN message will be copied into the foreground buffer RxFG, and the RXF
flag will never be set.
ID28
IDR0
ID21 ID20
ID10
IDR0
ID3 ID2
IDR1
ID15 ID14
IDR1 IDE
IDR2
ID7 ID6
IDR3
RTR
ID10 IDR2 ID3 ID10 IDR3 ID3
AM7 CIDMR0 AM0 AM7 CIDMR1 AM0 AM7 CIDMR2 AM0 AM7 CIDMR3 AM0
AC7 CIDAR0 AC0 AC7 CIDAR1 AC0 AC7 CIDAR2 AC0 AC7 CIDAR3 AC0
ID Accepted (Filter 0 Hit)
D
Figure D-3 32-bit Maskable Identifier Acceptance Filter
MOTOROLA
D-8
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
223
Freescale Semiconductor, Inc.
ID28
IDR0 ID21 ID20
IDR1 ID15 ID14
ID10
IDR0
IDR1 IDE
ID3 ID2
IDR2
ID7 ID6
IDR3
RTR
ID10 IDR2 ID3 ID10 IDR3 ID3
Freescale Semiconductor, Inc...
AM7 CIDMR0 AM0 AM7 CIDMR1 AM0
AC7 CIDAR0 AC0 AC7 CIDAR1 AC0
ID Accepted (Filter 0 Hit)
AM7 CIDMR2 AM0 AM7 CIDMR3 AM0
AC7 CIDAR2 AC0 AC7 CIDAR3 AC0
ID Accepted (Filter 1 Hit)
Figure D-4 16-bit Maskable Acceptance Filters
The Identifier Acceptance Registers (CIDAR0-7) define the acceptable patterns of the standard or
extended identifier (ID10 - ID0 or ID28 - ID0). Any of these bits can be marked ‘don’t care’ in the
Identifier Mask Registers (CIDMR0-7).
A filter hit is indicated to the application software by a set RXF (Receive Buffer Full Flag, see
Section D.12.6) and three bits in the Identifier Acceptance Control Register (see Section D.12.10).
These Identifier Hit Flags (IDHIT2-0) clearly identify the filter section that caused the acceptance.
They simplify the application software’s task to identify the cause of the receiver interrupt. In case
that more than one hit occurs (two or more filters match) the lower hit has priority.
A hit will also cause a receiver interrupt if enabled
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-9
224
Freescale Semiconductor, Inc.
ID28 IDR0 ID21 ID20 IDR1 ID15 ID14 IDR2 ID7 ID6 IDR3 RTR
ID10 IDR0 ID3 ID2 IDR1 IDE
ID10 IDR2 ID3 ID10 IDR3 ID3
Freescale Semiconductor, Inc...
AM7 CIDMR0AM0
AC7 CIDAR0 AC0
ID Accepted (Filter 0 Hit)
AM7 CIDMR1AM0
AC7 CIDAR1 AC0
ID Accepted (Filter 1 Hit)
AM7 CIDMR2AM0
AC7 CIDAR2 AC0
ID Accepted (Filter 2 Hit)
AM7 CIDMR3AM0
AC7 CIDAR3 AC0
ID Accepted (Filter 3 Hit)
Figure D-5 8-bit Maskable Acceptance Filters
D
MOTOROLA
D-10
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
225
Freescale Semiconductor, Inc.
D.5
Interrupts
Freescale Semiconductor, Inc...
The MSCAN12 supports four interrupt vectors mapped onto eleven different interrupt sources, any
of which can be individually masked (for details see Section D.12.6 to Section D.12.9):
•
Transmit Interrupt: At least one of the three transmit buffers is empty (not scheduled) and can
be loaded to schedule a message for transmission. The TXE flags of the empty message
buffers are set.
•
Receive Interrupt: A message has been successfully received and loaded into the foreground
receive buffer. This interrupt will be emitted immediately after receiving the EOF symbol. The
RXF flag is set.
•
Wake-Up Interrupt: An activity on the CAN bus occurred during MSCAN12 internal Sleep
Mode.
•
Error Interrupt: An overrun, error or warning condition occurred. The Receiver Flag Register
(CRFLG) will indicate one of the following conditions:
D.5.1
–
Overrun: An overrun condition as described in Section D.3.2 has occurred.
–
Receiver Warning: The Receive Error Counter has reached the CPU
Warning limit of 96.
–
Transmitter Warning: The Transmit Error Counter has reached the CPU
Warning limit of 96.
–
Receiver Error Passive: The Receive Error Counter has exceeded the Error
Passive limit of 127 and MSCAN12 has gone to Error Passive state.
–
Transmitter Error Passive: The Transmit Error Counter has exceeded the
Error Passive limit of 127 and MSCAN12 has gone to Error Passive state.
–
Bus Off: The Transmit Error Counter has exceeded 255 and MSCAN12 has
gone to Bus Off state.
Interrupt Acknowledge
Interrupts are directly associated with one or more status flags in either the MSCAN12 Receiver
Flag Register (CRFLG) or the MSCAN12 Transmitter Control Register (CTCR). Interrupts are
pending as long as one of the corresponding flags is set. The flags in above registers must be reset
within the interrupt handler in order to handshake the interrupt. The flags are reset through writing
a “1” to the corresponding bit position. A flag can not be cleared if the respective condition still
prevails.
Caution: Bit manipulation instructions (BSET) shall not be used to clear interrupt flags.
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
D
MOTOROLA
D-11
226
Freescale Semiconductor, Inc.
D.5.2
Interrupt Vectors
The MSCAN12 supports four interrupt vectors as shown in Table D-1. The vector addresses and
the relative interrupt priority are dependent on the chip integration to be defined.
Freescale Semiconductor, Inc...
Table D-1 MSCAN12 Interrupt Vectors
D
Function
Source
Local Mask
Wake-Up
WUPIF
WUPIE
RWRNIF
RWRNIE
TWRNIF
TWRNIE
RERRIF
RERRIE
TERRIF
TERRIE
BOFFIF
BOFFIE
OVRIF
OVRIE
Error
Interrupts
Receive
Transmit
D.6
RXF
RXFIE
TXE0
TXEIE0
TXE1
TXEIE1
TXE2
TXEIE2
Global Mask
I Bit
Protocol Violation Protection
The MSCAN12 will protect the user from accidentally violating the CAN protocol through
programming errors. The protection logic implements the following features:
•
The receive and transmit error counters can not be written or otherwise manipulated.
•
All registers which control the configuration of the MSCAN12 can not be modified while the
MSCAN12 is on-line. The SFTRES bit in CMCR0 (see Section D.12.2) serves as a lock to
protect the following registers:
•
–
MSCAN12 Module Control Register 1 (CMCR1)
–
MSCAN12 Bus Timing Register 0 and 1 (CBTR0, CBTR1)
–
MSCAN12 Identifier Acceptance Control Register (CIDAC)
–
MSCAN12 Identifier Acceptance Registers (CIDAR0-7)
–
MSCAN12 Identifier Mask Registers (CIDMR0-7)
The TxCAN pin is forced to Recessive if the CPU goes into STOP mode.
MOTOROLA
D-12
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
227
Freescale Semiconductor, Inc.
D.7
Low Power Modes
Freescale Semiconductor, Inc...
The MSCAN12 has three modes with reduced power consumption compared to Normal Mode. In
Sleep and Soft Reset Mode, power consumption is reduced by stopping all clocks except those to
access the registers. In Power Down Mode, all clocks are stopped and no power is consumed.
The WAI and STOP instruction put the MCU in low power consumption stand-by modes. Table D-2
summarizes the combinations of MSCAN12 and CPU modes. A particular combination of modes
is entered for the given settings of the bits CSWAI, SLPAK, and SFTRES. For all modes, an
MSCAN wake-up interrupt can occur only if SLPAK=WUPIE=1. While the CPU is in Wait Mode, the
MSCAN12 can be operated in Normal Mode and emit interrupts (registers can be accessed via
background debug mode).
Table D-2
MSCAN12 vs. CPU operating modes
CPU Mode
MSCAN Mode
Power Down
STOP
WAIT
CSWAI = X(1)
CSWAI = 1
SLPAK = X
SFTRES = X
SLPAK = X
SFTRES = X
RUN
Sleep
CSWAI = 0
SLPAK = 1
SFTRES = 0
CSWAI = X
SLPAK = 1
SFTRES = 0
Soft Reset
CSWAI = 0
SLPAK = 0
SFTRES = 1
CSWAI = X
SLPAK = 0
SFTRES = 1
Normal
CSWAI = 0
SLPAK = 0
SFTRES = 0
CSWAI = X
SLPAK = 0
SFTRES = 0
(1)
ÔXÕ means donÕt care.
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-13
228
Freescale Semiconductor, Inc.
D.7.1
MSCAN12 Sleep Mode
Freescale Semiconductor, Inc...
The CPU can request the MSCAN12 to enter this low-power mode by asserting the SLPRQ bit in
the Module Configuration Register (see Figure D-6). The time when the MSCAN12 will then enter
Sleep Mode depends on its current activity:
•
if it is transmitting, it will continue to transmit until there is no more message to be transmitted,
and then go into Sleep Mode.
•
if it is receiving, it will wait for the end of this message and then go into Sleep Mode.
•
if it is neither transmitting nor receiving, it will immediately go into Sleep Mode.
MSCAN12 Running
SLPRQ = 0
SLPAK = 0
MCU
MCU
or MSCAN12
MSCAN12 Sleeping
Sleep Request
SLPRQ = 1
SLPAK = 1
SLPRQ = 1
SLPAK = 0
MSCAN12
Figure D-6 Sleep Request / Acknowledge Cycle
D
The application software must avoid to set up a transmission (by clearing one or more TXE flag(s))
and immediately request Sleep Mode (by setting SLPRQ). It will then depend on the exact
sequence of operations whether the MSCAN12 will start transmitting or go into Sleep Mode
directly.
MOTOROLA
D-14
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
229
Freescale Semiconductor, Inc.
During Sleep Mode, the SLPAK flag is set. The application software should use this flag as a
handshake indication for the request to go into Sleep Mode. When in Sleep Mode, the MSCAN12
stops its own clocks and the TxCAN pin will stay in recessive state.
Freescale Semiconductor, Inc...
The MSCAN12 will leave Sleep Mode (wake-up) when
•
bus activity occurs or
•
the MCU clears the SLPRQ bit.
Note:
D.7.2
The MCU cannot clear the SLPRQ bit before the MSCAN12 is in Sleep Mode
(SLPAK = 1).
MSCAN12 Soft Reset Mode
In Soft Reset Mode, the MSCAN12 is stopped. Registers can still be accessed. This mode is used
to initialize the module configuration, bit timing, and the CAN message filter. See Section D.12.2
for a complete description of the Soft Reset Mode.
D.7.3
MSCAN12 Power Down Mode
The MSCAN12 is in Power Down Mode when
•
the CPU is in Stop Mode or
•
the CPU is in Wait Mode and the CSWAI bit is set (see Section D.12.2).
When entering the Power Down Mode, the MSCAN12 immediately stops all ongoing transmissions
and receptions, potentially causing CAN protocol violations. The user is responsible to take care
that the MSCAN12 is not active when Power Down Mode is entered. The recommended procedure
is to bring the MSCAN12 into Sleep Mode before the STOP instruction - or the WAI instruction, if
CSWAI is set - is executed.
To protect the CAN bus system from fatal consequences of violations to the above rule, the
MSCAN12 will drive the TxCAN pin into recessive state.
In Power Down Mode, no registers can be accessed.
D.7.4
Programmable Wake-Up Function
The MSCAN12 can be programmed to apply a low-pass filter function to the RxCAN input line
while in Sleep Mode (see control bit WUPM in the Module Control Register, Section D.12.3). This
feature can be used to protect the MSCAN12 from wake-up due to short glitches on the CAN bus
lines. Such glitches can result from electromagnetic inference within noisy environments.
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
D
MOTOROLA
D-15
230
Freescale Semiconductor, Inc.
D.8
Timer Link
Freescale Semiconductor, Inc...
The MSCAN12 will generate a timer signal whenever a valid frame has been received. Because
the CAN specification defines a frame to be valid if no errors occurred before the EOF field has
been transmitted successfully, the timer signal will be generated right after the EOF. A pulse of one
bit time is generated. As the MSCAN12 receiver engine also receives the frames being sent by
itself, a timer signal will also be generated after a successful transmission.
The previously described timer signal can be routed into the on-chip Timer Interface Module (TIM
/ ECT). This signal is connected to the Timer n Channel m input† under the control of the Timer
Link Enable (TLNKEN) bit in CMCR0.
After Timer n has been programmed to capture rising edge events it can be used under software
control to generate 16-bit time stamps which can be stored with the received message.
D.9
Clock System
Figure D-7 shows the structure of the MSCAN12 clock generation circuitry. With this flexible
clocking scheme the MSCAN12 is able to handle CAN bus rates ranging from 10 kbps up to 1
Mbps.
The Clock Source bit (CLKSRC) in the MSCAN12 Module Control Register (CMCR1) (see
Section D.12.4) defines whether the MSCAN12 is connected to the output of the crystal oscillator
(EXTALi) or to a clock twice as fast as the system clock (ECLK).
The clock source has to be chosen such that the tight oscillator tolerance requirements (up to
0.4%) of the CAN protocol are met. Additionally, for high CAN bus rates (1 Mbps), a 50% duty cycle
of the clock is required.
For microcontrollers without the CGM module, CGMCANCLK is driven from the crystal oscillator
(EXTALi).
D
†
The timer channel being used for the timer link is integration dependent.
MOTOROLA
D-16
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
231
Freescale Semiconductor, Inc.
CGM
MSCAN12
2 X PCLK/ECLK
CGMCANCLK
Freescale Semiconductor, Inc...
CLKSRC
Prescaler
(1 .. 64)
time quanta
clock
CLKSRC
EXTALi
Figure D-7 Clocking Scheme
A programmable prescaler is used to generate out of MSCANCLK the time quanta (Tq) clock. A
time quantum is the atomic unit of time handled by the MSCAN12. A bit time is subdivided into
three segments†:
•
SYNC_SEG: This segment has a fixed length of one time quantum. Signal edges are expected
to happen within this section.
•
Time segment 1: This segment includes the PROP_SEG and the PHASE_SEG1 of the CAN
standard. It can be programmed by setting the parameter TSEG1 to consist of 4 to 16 time
quanta.
•
Time segment 2: This segment represents the PHASE_SEG2 of the CAN standard. It can be
programmed by setting the TSEG2 parameter to be 2 to 8 time quanta long.
The Synchronisation Jump Width can be programmed in a range of 1 to 4 time quanta by setting
the SJW parameter.
Above parameters can be set by programming the Bus Timing Registers (CBTR0-1, see
Section D.12.4 and Section D.12.5).
It is the user’s responsibility to make sure that his bit time settings are in compliance with the CAN
standard. Figure D-3 gives an overview on the CAN conforming segment settings and the related
parameter values.
D
†
For further explanation of the under-lying concepts please refer to ISO/DIS 11519-1, Section
10.3.
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-17
232
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
NRZ Signal
SYNC
_SEG
(PROP_SEG + PHASE_SEG1)
(PHASE_SEG2)
1
4 ... 16
2 ... 8
Time Segment 1
Time Seg. 2
8... 25 Time Quanta
= 1 Bit Time
Transmit Point
Sample Point
(single or triple sampling)
Figure D-8 Segments within the Bit Time
Table D-3 CAN Standard Compliant Bit Time Segment Settings
Time Segment 1
TSEG1
Time Segment 2
TSEG2
Synchron.
Jump Width
SJW
5 .. 10
4 .. 9
2
1
1 .. 2
0 .. 1
4 .. 11
3 .. 10
3
2
1 .. 3
0 .. 2
5 .. 12
4 .. 11
4
3
1 .. 4
0 .. 3
6 .. 13
5 .. 12
5
4
1 .. 4
0 .. 3
7 .. 14
6 .. 13
6
5
1 .. 4
0 .. 3
8 .. 15
7 .. 14
7
6
1 .. 4
0 .. 3
9 .. 16
8 .. 15
8
7
1 .. 4
0 .. 3
D
MOTOROLA
D-18
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
233
Freescale Semiconductor, Inc.
D.10
Memory Map
The MSCAN12 occupies 128 Byte in the CPU12 memory space. The absolute mapping is
implementation dependent with the base address being a multiple of 128. The background receive
buffer can only be read in test mode.
Freescale Semiconductor, Inc...
$xx00
$xx08
$xx09
$xx0D
$xx0E
$xx0F
$xx10
$xx1F
$xx20
$xx3C
$xx3D
$xx3F
$xx40
$xx4F
$xx50
$xx5F
$xx60
$xx6F
$xx70
$xx7F
CONTROL REGISTERS
9 BYTES
RESERVED
5 BYTES
ERROR COUNTERS
2 BYTES
IDENTIFIER FILTER
16 BYTES
RESERVED
29 BYTES
PORT CAN REGISTERS
3 BYTES
RECEIVE BUFFER
TRANSMIT BUFFER 0
TRANSMIT BUFFER 1
TRANSMIT BUFFER 2
Figure D-9 MSCAN12 Memory Map
Note:
Due to design requirements, the absolute addresses and bit locations may change with
later releases of the specification.
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-19
234
Freescale Semiconductor, Inc.
D.11
Programmer’s Model of Message Storage
Freescale Semiconductor, Inc...
The following section details the organisation of the receive and transmit message buffers and the
associated control registers. For reasons of programmer interface simplification, the receive and
transmit message buffers have the same outline. Each message buffer allocates 16 byte in the
memory map containing a 13 byte data structure. An additional Transmit Buffer Priority Register
(TBPR) is defined for the transmit buffers.
Table D-4 Message Buffer Organisation
Address
Register Name
xxb0
Identifier Register 0
xxb1
Identifier Register 1
xxb2
Identifier Register 2
xxb3
Identifier Register 3
xxb4
Data Segment Register 0
xxb5
Data Segment Register 1
xxb6
Data Segment Register 2
xxb7
Data Segment Register 3
xxb8
Data Segment Register 4
xxb9
Data Segment Register 5
xxbA
Data Segment Register 6
xxbB
Data Segment Register 7
xxbC
Data Length Register
xxbD
Transmit Buffer Priority Register(1)
xxbE
unused
xxbF
unused
(1)
D.11.1
Not Applicable for Receive Buffers
Message Buffer Outline
Figure D-10 shows the common 13 byte data structure of receive and transmit buffers for extended
identifiers. The mapping of standard identifiers into the IDR registers is shown in Figure D-11. All
bits of the 13 byte data structure are undefined out of reset.
D
MOTOROLA
D-20
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
235
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
Register
Address
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
Identifier register 0 (IDR0)
$xxb0
ID28
ID27
ID26
Identifier register 1 (IDR1)
$xxb1
ID20
ID19
ID18
ID25
ID24
ID23
ID22
ID21
ID17
ID16
ID15
Identifier register 2 (IDR2)
$xxb2
ID14
ID13
ID12
ID11
Identifier register 3 (IDR3)
$xxb3
ID6
ID5
ID4
ID3
ID10
ID9
ID8
ID7
ID2
ID1
ID0
RTR
Data segment register 0 (DSR0)
$xxb4
DB7
DB6
DB5
Data segment register 1 (DSR1)
$xxb5
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB4
DB3
DB2
DB1
DB0
Data segment register 2 (DSR2)
$xxb6
DB7
DB6
Data segment register 3 (DSR3)
$xxb7
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB5
DB4
DB3
DB2
DB1
DB0
Data segment register 4 (DSR4)
$xxb8
DB7
Data segment register 5 (DSR5)
$xxb9
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Data segment register 6 (DSR6)
$xxbA
Data segment register 7 (DSR7)
$xxbB
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
Data length register (DLR)
$xxbC
DLC3
DLC2
DLC1
DLC0
SRR (1) IDE (1)
Figure D-10 Receive/transmit message buffer extended identifier
Register
Address
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
Identifier register 0 (IDR0)
$xxb0
ID10
ID9
ID8
ID7
ID6
ID5
ID4
ID3
Identifier register 1 (IDR1)
$xxb1
ID2
ID1
ID0
RTR
IDE (0)
Identifier register 2 (IDR2)
$xxb2
Identifier register 3 (IDR3)
$xxb3
Figure D-11 Standard identifier mapping
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-21
236
Freescale Semiconductor, Inc.
D.11.2
Identifier Registers (IDRn)
The identifiers consist of either 11 bits (ID10 – ID0) for the standard, or 29 bits (ID28 - ID0) for the
extended format. ID10/28 is the most significant bit and is transmitted first on the bus during the
arbitration procedure. The priority of an identifier is defined to be highest for the smallest binary
number.
Freescale Semiconductor, Inc...
SRR - Substitute Remote Request
This fixed recessive bit is used only in extended format. It must be set to 1 by the user for
transmission buffers and will be stored as received on the CAN bus for receive buffers.
IDE — ID Extended
This flag indicates whether the extended or standard identifier format is applied in this buffer. In
the case of a receive buffer the flag is set as being received and indicates to the CPU how to
process the buffer identifier registers. In the case of a transmit buffer the flag indicates to the
MSCAN12 what type of identifier to send.
1 (set)
–
Extended format (29 bit)
0 (clear) –
Standard format (11 bit)
RTR — Remote transmission request
This flag reflects the status of the Remote Transmission Request bit in the CAN frame. In the case
of a receive buffer it indicates the status of the received frame and allows to support the
transmission of an answering frame in software. In the case of a transmit buffer this flag defines
the setting of the RTR bit to be sent.
1 (set)
–
0 (clear) –
Remote frame
Data frame
D
MOTOROLA
D-22
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
237
Freescale Semiconductor, Inc.
D.11.3
Data Length Register (DLR)
This register keeps the data length field of the CAN frame.
Freescale Semiconductor, Inc...
DLC3 – DLC0 — Data length code bits
The data length code contains the number of bytes (data byte count) of the respective message.
At the transmission of a remote frame, the data length code is transmitted as programmed while
the number of transmitted bytes is always 0. The data byte count ranges from 0 to 8 for a data
frame. Table D-5 shows the effect of setting the DLC bits.
Table D-5 Data length codes
Data length code
D.11.4
DLC3
DLC2
DLC1
DLC0
Data byte
count
0
0
0
0
0
0
0
0
1
1
0
0
1
0
2
0
0
1
1
3
0
1
0
0
4
0
1
0
1
5
0
1
1
0
6
0
1
1
1
7
1
0
0
0
8
Data Segment Registers (DSRn)
The eight data segment registers contain the data to be transmitted or being received. The number
of bytes to be transmitted or being received is determined by the data length code in the
corresponding DLR.
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-23
238
Freescale Semiconductor, Inc.
D.11.5
Transmit Buffer Priority Registers (TBPR)
Address
Transmitbufferpriorityreg.isters(TBPR)
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
$xxbD PRIO7 PRIO6 PRIO5 PRIO4 PRIO3 PRIO2 PRIO1 PRIO0 undefined
Freescale Semiconductor, Inc...
PRIO7 - PRIO0— Local Priority
This field defines the local priority of the associated message buffer. The local priority is used for
the internal priorisation process of the MSCAN12 and is defined to be highest for the smallest
binary number. The MSCAN12 implements the following internal priorisation mechanism:
•
All transmission buffers with a cleared TXE flag participate in the priorisation immediately
before the SOF (Start of Frame) is sent.
•
The transmission buffer with the lowest local priority field wins the priorisation.
•
In cases of more than one buffer having the same lowest priority the message buffer with the
lower index number wins.
Caution: To ensure data integrity, no registers of the transmit buffers should be written to while
the associated TXE flag is cleared.
Caution: To ensure data integrity, no registers of the receive buffer shall be read while the RXF
flag is cleared.
D.12
Programmer’s Model of Control Registers
D.12.1
Overview
The programmer’s model has been laid out for maximum simplicity and efficiency. The following
figure gives an overview of the control register block of the MSCAN12:
D
MOTOROLA
D-24
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
239
Freescale Semiconductor, Inc.
Table D-6 MSCAN12 Control Register Structure
Freescale Semiconductor, Inc...
Register Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
CMCR0
$xx00
0
0
CSWAI
SYNCH
TLNKEN
SLPAK
SLPRQ
SFTRES
CMCR1
$xx01
0
0
0
0
0
LOOPB
WUPM
CLKSRC
CBTR0
$xx02
SJW1
SJW0
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0
CBTR1
$xx03
SAMP
TSEG22
TSEG21
TSEG20
TSEG13
TSEG12
TSEG11
TSEG10
CRFLG
$xx04
WUPIF
RWRNIF
TWRNIF
RERRIF
TERRIF
BOFFIF
OVRIF
RXF
CRIER
$xx05
WUPIE
RWRNIE
TWRNIE
RERRIE
TERRIE
BOFFIE
OVRIE
RXFIE
CTFLG
$xx06
0
ABTAK2
ABTAK1
ABTAK0
0
TXE2
TXE1
TXE0
CTCR
$xx07
0
ABTRQ2
ABTRQ1
ABTRQ0
0
TXEIE2
TXEIE1
TXEIE0
CIDAC
$xx08
0
0
IDAM1
IDAM0
0
IDHIT2
IDHIT1
IDHIT0
reserved
$xx09$xx0D
CRXERR
$xx0E
RXERR7
RXERR6
RXERR5
RXERR4
RXERR3
RXERR2
RXERR1
RXERR0
CTXERR
$xx0F
TXERR7
TXERR6
TXERR5
TXERR4
TXERR3
TXERR2
TXERR1
TXERR0
CIDAR0
$xx10
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDAR1
$xx11
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDAR2
$xx12
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDAR3
$xx13
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDMR0
$xx14
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDMR1
$xx15
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDMR2
$xx16
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDMR3
$xx17
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDAR4
$xx18
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDAR5
$xx19
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDAR6
$xx1A
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDAR7
$xx1B
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
CIDMR4
$xx1C
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDMR5
$xx1D
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDMR6
$xx1E
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
CIDMR7
$xx1F
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
reserved
$xx20$xx3C
PCTLCAN
$xx3D
0
0
0
0
0
0
PUECAN
RDRCAN
PORTCAN
$xx3E
PCAN7
PCAN6
PCAN5
PCAN4
PCAN3
PCAN2
TxCan
RxCan
DDRCAN
$xx3F
0
0
CAN PROTOCOL
Rev. 3
DDRCAN7 DDRCAN6 DDRCAN5 DDRCAN4 DDRCAN3 DDRCAN2
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
D
MOTOROLA
D-25
240
Freescale Semiconductor, Inc.
D.12.2
MSCAN12 Module Control Register 0 (CMCR0)
Modulecontrolregister0(CMCR0)
Address
bit7
bit6
$xx00
0
0
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
CSWAI SYNCH TLNKEN SLPAK SLPRQ SFTRES 00100001
Freescale Semiconductor, Inc...
CSWAI — CAN Stops in Wait Mode
1 (set)
–
0 (clear) –
The module is not affected during WAIT mode.
SYNCH — Synchronized Status
This bit indicates whether the MSCAN12 is synchronized to the CAN bus and as such can
participate in the communication process.
1 (set)
–
0 (clear) –
MSCAN12 is synchronized to the CAN bus.
MSCAN12 is not synchronized to the CAN bus.
TLNKEN - Timer Enable
This flag is used to establish a link between the MSCAN12 and the on-chip timer (see Section D.8).
1 (set)
–
0 (clear) –
The MSCAN12 timer signal output is connected to the timer input.
The port is connected to the timer input.
SLPAK — Sleep Mode Acknowledge
This flag indicates whether the MSCAN12 is in module internal Sleep Mode. It shall be used as a
handshake for the Sleep Mode request (see Section D.7.1).
1 (set)
–
0 (clear) –
Sleep – The MSCAN12 is in Sleep Mode.
Wake-up – The MSCAN12 is not in Sleep Mode.
SLPRQ — Sleep request, go to Sleep Mode
This flag allows to request the MSCAN12 to go into an internal power-saving mode (see
Section D.7.1).
1 (set)
–
0 (clear) –
D
The module ceases to be clocked during WAIT mode.
Sleep request – The MSCAN12 will go into Sleep Mode.
Wake-up – The MSCAN12 will function normally.
SFTRES— Soft Reset
When this bit is set by the CPU, the MSCAN12 immediately enters the soft reset state. Any
ongoing transmission or reception is aborted and synchronisation to the bus is lost.
MOTOROLA
D-26
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
241
Freescale Semiconductor, Inc.
The following registers will go into and stay in the same state as out of hard reset: CMCR0,
CRFLG, CRIER, CTFLG, CTCR.
Freescale Semiconductor, Inc...
The registers CMCR1, CBTR0, CBTR1, CIDAC, CIDAR0-7, CIDMR0-7 can only be written by the
CPU when the MSCAN12 is in soft reset state. The values of the error counters are not affected
by soft reset.
When this bit is cleared by the CPU, MSCAN12 will try to synchronize to the CAN bus: If the
MSCAN12 is not in bus-off state it will be synchronized after 11 recessive bits on the bus; if the
MSCAN12 is in bus-off state it continues to wait for 128 occurrences of 11 recessive bits.
Clearing SFTRES and writing to other bits in CMCR0 must be in separate instructions.
1 (set)
–
0 (clear) –
D.12.3
MSCAN12 in soft reset state.
Normal operation.
MSCAN12 Module Control Register 1 (CMCR1)
Modulecontrolregister1(CMCR1)
Address
bit7
bit6
bit5
bit4
bit3
$xx01
0
0
0
0
0
bit2
bit1
bit0
State
onreset
LOOPB WUPM CLKSRC 00000000
LOOPB - Loop Back Self Test Mode
When this bit is set the MSCAN12 performs an internal loop back which can be used for self test
operation: the bit stream output of the transmitter is fed back to the receiver. The RxCAN input pin
is ignored and the TxCAN output goes to the recessive state (1). Note that in this state the
MSCAN12 ignores the ACK bit to insure proper reception of its own message and will treat
messages being received while in transmission as received messages from remote nodes.
1 (set)
–
0 (clear) –
Activate loop back self test mode.
Normal operation.
WUPM - Wake-Up Mode
This flag defines whether the integrated low-pass filter is applied to protect the MSCAN12 from
spurious wake-ups (see Section D.7.4).
1 (set)
–
0 (clear) –
MSCAN12 will wake up the CPU only in case of dominant pulse on
the bus which has a length of at least approximately Twup.
MSCAN12 will wake up the CPU after any recessive to dominant
edge on the CAN bus.
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-27
242
Freescale Semiconductor, Inc.
CLKSRC - MSCAN12 Clock Source
This flag defines which clock source the MSCAN12 module is driven from (only for system with
CGM module; see Section D.9, Figure D-7).
1 (set)
–
Freescale Semiconductor, Inc...
0 (clear) –
Note:
The MSCAN12 clock source is twice the frequency of ECLK.
The MSCAN12 clock source is EXTALi.
The CMCR1 register can only be written if the SFTRES bit in CMCR0 is set.
D.12.4
MSCAN12 Bus Timing Register 0 (CBTR0)
Address
Bustimingregister0(CBTR0)
$xx02
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
SJW1 SJW0 BRP5 BRP4 BRP3 BRP2 BRP1 BRP0 00000000
SJW1, SJW0 — Synchronization Jump Width
The synchronization jump width defines the maximum number of time quanta (Tq) clock cycles by
which a bit may be shortened, or lengthened, to achieve resynchronization on data transitions on
the bus (see Table D-7).
Table D-7 Synchronization jump width
SJW1
SJW0
Synchronization jump width
0
0
1 Tq clock cycle
0
1
2 Tq clock cycles
1
0
3 Tq clock cycles
1
1
4 Tq clock cycles
BRP5 – BRP0 — Baud Rate Prescaler
These bits determine the time quanta (Tq) clock, which is used to build up the individual bit timing,
according to Table D-8.
D
MOTOROLA
D-28
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
243
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Table D-8 Baud rate prescaler
Note:
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0
Prescaler value (P)
0
0
0
0
0
0
1
0
0
0
0
0
1
2
0
0
0
0
1
0
3
0
0
0
0
1
1
4
:
:
:
:
:
:
:
:
:
:
:
:
:
:
1
1
1
1
1
1
64
The CBTR0 register can only be written if the SFTRES bit in CMCR0 is set.
D.12.5
MSCAN12 Bus Timing Register 1 (CBTR1)
Address
Bustimingregister1(CBTR1)
$xx03
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
SAMP TSEG22TSEG21‘TSEG20TSEG13TSEG12TSEG11 TSEG10 00000000
SAMP — Sampling
This bit determines the number of samples of the serial bus to be taken per bit time. If set three
samples per bit are taken, the regular one (sample point) and two preceding samples, using a
majority rule. For higher bit rates SAMP should be cleared, which means that only one sample will
be taken per bit.
1 (set)
–
0 (clear) –
Three samples per bit.
One sample per bit.
TSEG22 – TSEG10 — Time Segment
Time segments within the bit time fix the number of clock cycles per bit time, and the location of
the sample point.
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-29
244
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Table D-9 Time segment syntax
SYNC_SEG
System expects transitions to occur on the bus
this period.
during
Transmit point
A node in transmit mode will transfer a new
the CAN bus at this point.
Sample point
A node in receive mode will sample the bus at this point.
If the three samples per bit option is selected then this
point marks the position of the third sample.
value to
Time segment 1 (TSEG1) and time segment 2 (TSEG2) are programmable as shown in
Table D-10.
Table D-10 Time segment values
TSEG
13
TSEG
12
TSEG
11
TSEG
10
Time segment 1
TSEG
22
TSEG
21
TSEG
20
Time segment 2
0
0
0
0
1 Tq clock cycle
0
0
0
1 Tq clock cycle
0
0
0
1
2 Tq clock cycles
0
0
1
2 Tq clock cycles
0
0
1
0
3 Tq clock cycles
.
.
.
.
0
0
1
1
4 Tq clock cycles
.
.
.
.
.
.
.
.
.
1
1
1
8 Tq clock cycles
.
.
.
.
.
1
1
1
1
16 Tq clock cycles
The bit time is determined by the oscillator frequency, the baud rate prescaler, and the number of
time quanta (Tq) clock cycles per bit (as shown above).
Note:
The CBTR1 register can only be written if the SFTRES bit in CMCR0 is set.
D
MOTOROLA
D-30
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
245
Freescale Semiconductor, Inc.
D.12.6
MSCAN12 Receiver Flag Register (CRFLG)
Address
Freescale Semiconductor, Inc...
Receiverflagregister(CRFLG)
$xx04
bit7
bit6
bit5
bit4
bit3
bit2
bit1
WUPIF RWRNIFTWRNIFRERRIF TERRIF BOFFIF OVRIF
bit0
State
onreset
RXF
00000000
All bits of this register are read and clear only. A flag can be cleared by writing a 1 to the
corresponding bit position. A flag can only be cleared when the condition which caused the setting
is no more valid. Writing a ‘0’ has no effect on the flag setting. Every flag has an associated
interrupt enable flag in the CRIER register. A hard or soft reset will clear the register.
WUPIF — Wake-up Interrupt Flag
If the MSCAN12 detects bus activity whilst it is in Sleep Mode, it clears the SLPAK bit in the
CMCR0 register; the WUPIF bit will then be set. If not masked, a Wake-Up interrupt is pending
while this flag is set.
1 (set)
–
0 (clear) –
MSCAN12 has detected activity on the bus and requested wake-up.
No wake-up activity has been observed while in Sleep Mode.
RWRNIF — Receiver Warning Interrupt Flag
This bit will be set when the MSCAN12 goes into warning status due to the Receive Error counter
(REC) being in the range of 96 to 127 and neither one of the Error interrupt flags or the Bus-Off
interrupt flag is set†. If not masked, an Error interrupt is pending while this flag is set.
1 (set)
–
0 (clear) –
MSCAN12 has gone into receiver warning status.
No receiver warning status has been reached.
TWRNIF — Transmitter Warning Interrupt Flag
This bit will be set when the MSCAN12 goes into warning status due to the Transmit Error counter
(TEC) being in the range of 96 to 127 and neither one of the Error interrupt flags or the Bus-Off
interrupt flag is set‡. If not masked, an Error interrupt is pending while this flag is set.
1 (set)
–
0 (clear) –
MSCAN12 has gone into transmitter warning status.
No transmitter warning status has been reached.
†
RWRNIF = (96 ≤ REC < 128) & RERRIF & TERRIF & BOFFIF
‡
TWRNIF = (96 ≤ TEC < 128) & RERRIF & TERRIF & BOFFIF
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
D
MOTOROLA
D-31
246
Freescale Semiconductor, Inc.
RERRIF — Receiver Error Passive Interrupt Flag
This bit will be set when the MSCAN12 goes into error passive status due to the Receive Error
counter exceeding 127 and the Bus-Off interrupt flag is not set†. If not masked, an Error interrupt
is pending while this flag is set.
1 (set)
–
Freescale Semiconductor, Inc...
0 (clear) –
MSCAN12 has gone into receiver error passive status.
No receiver error passive status has been reached.
TERRIF — Transmitter Error Passive Interrupt Flag
This bit will be set when the MSCAN12 goes into error passive status due to the Transmit Error
counter exceeding 127 and the Bus-Off interrupt flag is not set‡. If not masked, an Error interrupt
is pending while this flag is set.
1 (set)
–
0 (clear) –
MSCAN12 has gone into transmitter error passive status.
No transmitter error passive status has been reached.
BOFFIF — Bus-Off Interrupt Flag
This bit will be set when the MSCAN12 goes into bus-off status, due to the Transmit Error counter
exceeding 255. It cannot be cleared before the MSCAN12 has monitored 128 times 11
consecutive ‘recessive’ bits on the bus. If not masked, an Error interrupt is pending while this flag
is set.
1 (set)
–
0 (clear) –
MSCAN12 has gone into bus-off status.
No bus-off status has been reached.
OVRIF — Overrun Interrupt Flag
This bit will be set when a data overrun condition occurs. If not masked, an Error interrupt is
pending while this flag is set.
1 (set)
–
0 (clear) –
A data overrun has been detected.
No data overrun has occurred.
RXF — Receive Buffer Full
The RXF flag is set by the MSCAN12 when a new message is available in the foreground receive
buffer. This flag indicates whether the buffer is loaded with a correctly received message. After the
CPU has read that message from the receive buffer, the RXF flag must be handshaken in order to
D
†
RERRIF = (128 ≤ REC ≤ 255) & BOFFIF
‡
TERRIF = (128 ≤ TEC ≤ 255) & BOFFIF: TERRIF is set at the end of the Bus-Off period (due
to counting 128 * 11 consecutive ‘recessive’ bits on the TEC). Thus TERRIF should be cleared
together with BOFFIF.
MOTOROLA
D-32
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
247
Freescale Semiconductor, Inc.
release the buffer. A set RXF flag prohibits the exchange of the background receive buffer into the
foreground buffer. If not masked, a Receive interrupt is pending while this flag is set.
1 (set)
–
0 (clear) –
Freescale Semiconductor, Inc...
Note:
The receive buffer is full. A new message is available.
The receive buffer is released (not full).
The CRFLG register is held in the reset state when the SFTRES bit in CMCR0 is set.
D.12.7
MSCAN12 Receiver Interrupt Enable Register (CRIER)
Address
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
Receiverinterruptenableregister(CRIER) $xx05 WUPIE RWRNIE TWRNIERERRIETERRIE BOFFIE OVRIE RXRIE 00000000
WUPIE — Wake-up Interrupt Enable
1 (set)
–
0 (clear) –
A wake-up event will result in a wake-up interrupt.
No interrupt will be generated from this event.
RWRNIE — Receiver Warning Interrupt Enable
1 (set)
–
0 (clear) –
A receiver warning status event will result in an error interrupt.
No interrupt will be generated from this event.
TWRNIE — Transmitter Warning Interrupt Enable
1 (set)
–
0 (clear) –
A transmitter warning status event will result in an error interrupt.
No interrupt will be generated from this event.
RERRIE — Receiver Error Passive Interrupt Enable
1 (set)
–
0 (clear) –
A receiver error passive status event will result in an error interrupt.
No interrupt will be generated from this event.
TERRIE — Transmitter Error Passive Interrupt Enable
1 (set)
–
0 (clear) –
A transmitter error passive status event will result in an error interrupt.
No interrupt will be generated from this event.
BOFFIE — Bus-Off Interrupt Enable
1 (set)
–
A bus-off event will result in an error interrupt.
0 (clear) –
No interrupt will be generated from this event.
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
D
MOTOROLA
D-33
248
Freescale Semiconductor, Inc.
OVRIE — Overrun Interrupt Enable
1 (set)
–
0 (clear) –
An overrun event will result in an error interrupt.
No interrupt will be generated from this event.
RXFIE — Receiver Full Interrupt Enable
Freescale Semiconductor, Inc...
1 (set)
D
–
0 (clear) –
Note:
A receive buffer full (successful message reception) event will result
in a receive interrupt.
No interrupt will be generated from this event.
The CRIER register is held in the reset state when the SFTRES bit in CMCR0 is set.
D.12.8
MSCAN12 Transmitter Flag Register (CTFLG)
Transmitterflagregister(CTFLG)
Address
bit7
$xx06
0
bit6
bit5
bit4
ABTAK2 ABTAK1 ABTAK0
bit3
bit2
bit1
0
TXE2
TXE1
bit0
State
onreset
TXE0 00000111
All of the bits in this register are read and clear only. A flag can be cleared by writing a 1 to the
corresponding bit position. Writing a 0 has no effect on the flag setting. Every flag has an
associated interrupt enable flag in the CTCR register. A hard or soft reset will clear the register.
ABTAK2 - ABTAK0 — Abort Acknowledge
This flag acknowledges that a message has been aborted due to a pending abort request from the
CPU. After a particular message buffer has been flagged empty, this flag can be used by the
application software to identify whether the message has been aborted successfully or has been
sent in the meantime. The flag is reset implicitly whenever the associated TXE flag is set to 0.
1 (set)
–
0 (clear) –
The message has been aborted.
The message has not been aborted, thus has been sent out.
TXE2 - TXE0 —Transmitter Buffer Empty
This flag indicates that the associated transmit message buffer is empty, thus not scheduled for
transmission. The CPU must handshake (clear) the flag after a message has been set up in the
transmit buffer and is due for transmission. The MSCAN12 will set the flag after the message has
been sent successfully. The flag will also be set by the MSCAN12 when the transmission request
was successfully aborted due to a pending abort request (Section D.12.9). If not masked, a
Transmit interrupt is pending while this flag is set.
MOTOROLA
D-34
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
249
Freescale Semiconductor, Inc.
A reset of this flag will also reset the Abort Acknowledge (ABTAK, see above) and the Abort
Request (ABTRQ, see Section D.12.9) flags of the particular buffer.
1 (set)
–
0 (clear) –
Freescale Semiconductor, Inc...
Note:
The associated message buffer is empty (not scheduled).
The associated message buffer is full (loaded with a message due for
transmission).
The CTFLG register is held in the reset state when the SFTRES bit in CMCR0 is set.
D.12.9
MSCAN12 Transmitter Control Register (CTCR)
Address bit7
Transmittercontrolregister(CTCR)
$xx07
0
bit6
bit5
bit4
ABTRQ2 ABTRQ1 ABTRQ0
bit3
0
bit2
bit1
bit0
State
onreset
TXEIE2 TXEIE1 TXEIE0 00000000
ABTRQ2 - ABTRQ0 — Abort Request
The CPU sets this bit to request that an already scheduled message buffer (TXE = 0) shall be
aborted. The MSCAN12 will grant the request when the message is not already under
transmission. When a message is aborted the associated TXE and the Abort Acknowledge flag
(ABTAK, see Section D.12.8) will be set and an TXE interrupt will occur if enabled. The CPU can
not reset ABTRQx. ABTRQx is reset implicitly whenever the associated TXE flag is set.
1 (set)
–
0 (clear) –
Abort request pending.
No abort request.
The software must not clear one or more of the TXE flags in CTFGL and simultaneously set the
respective ABTRQ bit(s).
TXEIE2 - TXEIE0 — Transmitter Empty Interrupt Enable
1 (set)
–
0 (clear) –
Note:
A transmitter empty (transmit buffer available for transmission) event
will result in a transmitter empty interrupt.
No interrupt will be generated from this event.
The CTCR register is held in the reset state when the SFTRES bit in CMCR0 is set.
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-35
250
Freescale Semiconductor, Inc.
D.12.10
MSCAN12 Identifier Acceptance Control Register (CIDAC)
Identifieracceptancecontrolreg.(CIDAC)
Address
bit7
bit6
$xx08
0
0
bit5
bit4
IDAM1 IDAM0
bit3
0
bit2
bit1
bit0
State
onreset
IDHIT2 IDHIT1 IDHIT0 00000000
Freescale Semiconductor, Inc...
IDAM1- IDAM0— Identifier Acceptance Mode
D
The CPU sets these flags to define the identifier acceptance filter organisation (see Section D.4).
Table D-10 summarizes the different settings. In Filter Closed mode no messages will be accepted
such that the foreground buffer will never be reloaded.
Table D-11 Identifier Acceptance Mode Settings
IDAM1
IDAM0
Identifier Acceptance Mode
0
0
Two 32 bit Acceptance Filters
0
1
Four 16 bit Acceptance Filters
1
0
Eight 8 bit Acceptance Filters
1
1
Filter Closed
IDHIT2- IDHIT0— Identifier Acceptance Hit Indicator
The MSCAN12 sets these flags to indicate an identifier acceptance hit (see Section D.4).
Table D-10 summarizes the different settings.
Table D-12 Identifier Acceptance Hit Indication
IDHIT2
IDHIT1
IDHIT0
Identifier Acceptance Hit
0
0
0
Filter 0 Hit
0
0
1
Filter 1 Hit
0
1
0
Filter 2 Hit
0
1
1
Filter 3 Hit
1
0
0
Filter 4 Hit
1
0
1
Filter 5 Hit
1
1
0
Filter 6 Hit
1
1
1
Filter 7 Hit
The IDHIT indicators are always related to the message in the foreground buffer. When a message
gets copied from the background to the foreground buffer the indicators are updated as well.
MOTOROLA
D-36
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
251
Freescale Semiconductor, Inc.
Note:
D.12.11
The CIDAC register can only be written if the SFTRES bit in CMCR0 is set.
MSCAN12 Receive Error Counter (CRXERR)
Address
Freescale Semiconductor, Inc...
Receiveerrorcounter(CRXERR)
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
$xx0E RXERR7RXERR6RXERR5RXERR4RXERR3RXERR2RXERR1RXERR0 00000000
This register reflects the status of the MSCAN12 receive error counter. The register is read only.
D.12.12
MSCAN12 Transmit Error Counter (CTXERR)
Address
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
Transmiterrorcounter(CTXERR) $xx0F TXERR7 TXERR6 TXERR5 TXERR4 TXERR3 TXERR2 TXERR1 TXERR0 00000000
This register reflects the status of the MSCAN12 transmit error counter. The register is read only.
Note:
D.12.13
Both error counters must only be read when in Sleep or Soft Reset Mode.
MSCAN12 Identifier Acceptance Registers (CIDAR0-7)
On reception each message is written into the background receive buffer. The CPU is only
signalled to read the message however, if it passes the criteria in the identifier acceptance and
identifier mask registers (accepted); otherwise, the message will be overwritten by the next
message (dropped).
The acceptance registers of the MSCAN12 are applied on the IDR0 to IDR3 registers of incoming
messages in a bit by bit manner.
For extended identifiers all four acceptance and mask registers are applied. For standard
identifiers only the first two (IDAR0, IDAR1) are applied. In the latter case it is required to program
the three last bits (AC2 - AC0) in the mask register CIDMR1 to “don’t care”.
D
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
MOTOROLA
D-37
252
Freescale Semiconductor, Inc.
Register
Address
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
CIDAR0
$xx10
AC&
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
CIDAR1
$xx11
AC&
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
CIDAR2
$xx12
AC&
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
CIDAR3
$xx12
AC&
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
Freescale Semiconductor, Inc...
Figure D-12 Identifier acceptance registers (1ST bank)
D
Register
Address
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
CIDAR4
$xx18
AC&
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
CIDAR5
$xx19
AC&
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
CIDAR6
$xx1A
AC&
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
CIDAR7
$xx1B
AC&
AC6
AC5
AC4
AC3
AC2
AC1
AC0
undeÞned
Figure D-13 Identifier acceptance registers (2ND bank)
AC7 – AC0 — Acceptance Code Bits
AC7 – AC0 comprise a user defined sequence of bits with which the corresponding bits of the
related identifier register (IDRn) of the receive message buffer are compared. The result of this
comparison is then masked with the corresponding identifier mask register.
Note:
The CIDAR0-7 registers can only be written if the SFTRES bit in CMCR0 is set.
D.12.14
MSCAN12 Identifier Mask Registers (CIDMR0-7)
The identifier mask register specifies which of the corresponding bits in the identifier acceptance
register are relevant for acceptance filtering.
Register
Address
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
CIDMR0
$xx14
AM&
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
CIDMR1
$xx15
AM&
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
CIDMR2
$xx16
AM&
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
CIDMR3
$xx17
AM&
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
Figure D-14 Identifier mask registers (1ST bank)
MOTOROLA
D-38
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
253
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
Register
Address
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
CIDMR4
$xx1C
AM&
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
CIDMR5
$xx1D
AM&
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
CIDMR6
$xx1E
AM&
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
CIDMR7
$xx1F
AM&
AM6
AM5
AM4
AM3
AM2
AM1
AM0
undeÞned
Figure D-15 Identifier mask registers (2NDbank)
AM7 – AM0 — Acceptance Mask Bits
If a particular bit in this register is cleared this indicates that the corresponding bit in the identifier
acceptance register must be the same as its identifier bit, before a match will be detected. The
message will be accepted if all such bits match. If a bit is set, it indicates that the state of the
corresponding bit in the identifier acceptance register will not affect whether or not the message is
accepted.
Bit description:
1 (set)
–
0 (clear) –
Note:
Ignore corresponding acceptance code register bit.
Match corresponding acceptance code register and identifier bits.
The CIDMR0-7 registers can only be written if the SFTRES bit in CMCR0 is set.
D.12.15
MSCAN12 Port CAN Control Register (PCTLCAN)
PortCANcontrolreg.(PCTLCAN)
Address
bit7
bit6
bit5
bit4
bit3
bit2
$xx3D
0
0
0
0
0
0
bit1
bit0
State
onreset
PUECAN RDRCAN 00000000
The following bits control pins 7 through 2 of Port CAN. Pins 1 and 0 are reserved for the RxCan
(input only) and TxCan (output only) pins.
PUECAN — Pull Enable Port CAN
1 (set)
–
Pull mode enabled for Port CAN.
0 (clear) –
Pull mode disabled for Port CAN.
The pull mode (pull-up or pull-down) for Port CAN is defined in the chip specification.
CAN PROTOCOL
Rev. 3
THE MOTOROLA SCALEABLE CAN (MSCAN12)
For More Information
On This Product,
MODULE
Go to: www.freescale.com
D
MOTOROLA
D-39
254
Freescale Semiconductor, Inc.
RDRCAN — Reduced Drive Port CAN
1 (set)
–
Reduced drive enabled for Port CAN.
0 (clear) –
Reduced drive disabled for Port CAN.
Freescale Semiconductor, Inc...
D.12.16
MSCAN12 Port CAN Data Register (PORTCAN)
Address
PortCANdatareg.(PORTCAN)
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
State
onreset
$xx3E PCAN7 PCAN6 PCAN5 PCAN4 PCAN3 PCAN2 TxCAN RxCAN undefined
PCAN7 – PCAN2 — Port CAN Data Bits
Writing to PCANx stores the bit value in an internal bit memory. This value is driven to the
respective pin only if DDRCANx = 1.
Reading PCANx returns
•
the value of the internal bit memory driven to the pin, if DDRCANx = 1
•
the value of the respective pin, if DDRCANx = 0
Reading bits 1 and 0 returns the value of the TxCan and RxCan pins, respectively.
D.12.17
MSCAN12 Port CAN Data Direction Register (DDRCAN)
Address
bit7
bit6
bit5
bit4
bit3
bit2
PortCANdatadirectionreg.ister
$xx3F DDRCAN7DDRCAN6DDRCAN5DDRCAN4DDRCAN3DDRCAN2
(DDRCAN)
bit1
bit0
State
onreset
0
0
00000000
DDRCAN7 – DDRCAN2 — Data Direction Port CAN Bits
1 (set)
–
0 (clear) –
Respective I/O pin is configured for output.
Respective I/O pin is configured for input.
D
MOTOROLA
D-40
THE MOTOROLA SCALEABLE CAN (MSCAN12)
CAN PROTOCOL
For More Information
MODULE On This Product,
Rev. 3
Go to: www.freescale.com
255
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
GLOSSARY
This section contains abbreviations and specialist words used in this data
sheet and throughout the industry. Further information on many of the terms
may be gleaned from a variety of standard electronics text books.
$xxxx
The digits following the ‘$’ are in hexadecimal format.
%xxxx
The digits following the ‘%’ are in binary format.
A/D, ADC
Analog-to-digital (converter).
Bootstrap mode
In this mode the device automatically loads its internal memory from an
external source on reset and then allows this program to be executed.
Byte
Eight bits.
CAN
Controller area network.
CCR
Condition codes register; an integral part of the CPU.
CERQUAD
A ceramic package type, principally used for EPROM and high temperature
devices.
Clear
‘0’ — the logic zero state; the opposite of ‘set’.
CMOS
Complementary metal oxide semiconductor. A semiconductor technology
chosen for its low power consumption and good noise immunity.
COP
Computer operating properly. aka ‘watchdog’. This circuit is used to detect
device runaway and provide a means for restoring correct operation.
CPU
Central processing unit.
D/A, DAC
Digital-to-analog (converter).
EEPROM
Electrically erasable programmable read only memory. aka ‘EEROM’.
EPROM
Erasable programmable read only memory. This type of memory requires
exposure to ultra-violet wavelengths in order to erase previous data. aka
‘PROM’.
ESD
Electrostatic discharge.
Expanded mode
In this mode the internal address and data bus lines are connected to
external pins. This enables the device to be used in much more complex
systems, where there is a need for external memory for example.
TPG
CAN PROTOCOL
Rev. 3
GLOSSARY
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
i
256
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
EVS
Evaluation system. One of the range of platforms provided by Motorola for
evaluation and emulation of their devices.
HCMOS
High-density complementary metal oxide semiconductor. A semiconductor
technology chosen for its low power consumption and good noise immunity.
I/O
Input/output; used to describe a bidirectional pin or function.
Input capture
(IC) This is a function provided by the timing system, whereby an external
event is ‘captured’ by storing the value of a counter at the instant the event
is detected.
Interrupt
This refers to an asynchronous external event and the handling of it by the
MCU. The external event is detected by the MCU and causes a
predetermined action to occur.
IRQ
Interrupt request. The overline indicates that this is an active-low signal
format.
K byte
A kilo-byte (of memory); 1024 bytes.
LCD
Liquid crystal display.
LSB
Least significant byte.
M68HC05
Motorola’s family of 8-bit MCUs.
MCU
Microcontroller unit.
MI BUS
Motorola interconnect bus. A single wire, medium speed serial
communications protocol.
MSB
Most significant byte.
Nibble
Half a byte; four bits.
NRZ
Non-return to zero.
Opcode
The opcode is a byte which identifies the particular instruction and operating
mode to the CPU. See also: prebyte, operand.
Operand
The operand is a byte containing information the CPU needs to execute a
particular instruction. There may be from 0 to 3 operands associated with an
opcode. See also: opcode, prebyte.
Output compare
(OC) This is a function provided by the timing system, whereby an external
event is generated when an internal counter value matches a predefined
value.
PLCC
Plastic leaded chip carrier package.
PLL
Phase-locked loop circuit. This provides a method of frequency
multiplication, to enable the use of a low frequency crystal in a high
frequency circuit.
Prebyte
This byte is sometimes required to qualify an opcode, in order to fully specify
a particular instruction. See also: opcode, operand.
TPG
MOTOROLA
ii
GLOSSARY
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
257
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
Pull-down, pull-up These terms refer to resistors, sometimes internal to the device, which are
permanently connected to either ground or VDD.
PWM
Pulse width modulation. This term is used to describe a technique where the
width of the high and low periods of a waveform is varied, usually to enable
a representation of an analog value.
QFP
Quad flat pack package.
RAM
Random access memory. Fast read and write, but contents are lost when the
power is removed.
RFI
Radio frequency interference.
RTI
Real-time interrupt.
ROM
Read-only memory. This type of memory is programmed during device
manufacture and cannot subsequently be altered.
RS-232C
A standard serial communications protocol.
SAR
Successive approximation register.
SCI
Serial communications interface.
Set
‘1’ — the logic one state; the opposite of ‘clear’.
Silicon glen
An area in the central belt of Scotland, so called because of the
concentration of semiconductor manufacturers and users found there.
Single chip mode
In this mode the device functions as a self contained unit, requiring only I/O
devices to complete a system.
SPI
Serial peripheral interface.
Test mode
This mode is intended for factory testing.
TTL
Transistor-transistor logic.
UART
Universal asynchronous receiver transmitter.
VCO
Voltage controlled oscillator.
Watchdog
see ‘COP’.
Wired-OR
A means of connecting outputs together such that the resulting composite
output state is the logical OR of the state of the individual outputs.
Word
Two bytes; 16 bits.
XIRQ
Non-maskable interrupt request. The overline indicates that this has an
active-low signal format.
TPG
CAN PROTOCOL
Rev. 3
GLOSSARY
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
iii
258
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
THIS PAGE LEFT BLANK INTENTIONALLY
TPG
MOTOROLA
iv
GLOSSARY
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
259
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
INDEX
In this index numeric entries are placed first; page references in italics indicate that the reference is
to a figure.
16-bit maskable acceptance filters C-9
32-bit maskable identifier acceptance filters C-8
8-bit maskable acceptance filters C-10
A
ABTAK2 — ABTAK0 — abort acknowledge flag in CTFLG
C-33
ABTRQ2 — ABTRQ0 bit in CTCR C-34
AC7 — AC0 bits in CIADR0—3 C-37
AC7-AC0 bits in CACC A-14 D-38
ACK field
standard and extended formats 10-7
ACKER bit in STATH, STATL B-39
AM0-AM7 bits in CACM A-15 D-39
AM7 — AM0 bits in CIDMR0—3 C-38
AT bit in CCOM A-11
MCAN module A-2
MSCAN08 C-3
TOUCAN B-2
BOFF bit in CTRL0 B-31
BOFFIE bit in CRIER C-32
BOFFIF flag in CRFLG C-30
BOFINT bit in STATH, STATL B-40
BRP5 — BRP0 bits in CBTR0 C-27
BRP5-BRP0 bits in CBT0 A-16
BS bit in CSTAT A-11
BUS_STATE in STATH, STATL B-40
,
,
C
,
,
CACC – MCAN acceptance code register A-14 D-37
D-38
AC7-AC0 – acceptance code bits A-14 D-38
CACM – MCAN acceptance mask register A-15
AM0-AM7 – acceptance mask bits A-15 D-39
CAN
node status 5-1 12-1
CAN node
CAN layers, specification 1.2 2-2
CAN layers, specification 2.0 9-2
CAN protocol
arbitration 2-4 9-4
bus values 2-6 9-6
data link layer 8-1
error detection 2-4 9-4
information routing 2-1 9-1
message routing 2-2 9-3
object layer 1-1
physical layer 1-1
remote data request 2-3 9-3
sleep mode/wake-up 2-6 9-6
transfer layer 1-1
CAN system B-3 B-3
MSCAN08 C-3
CBT0 – MCAN bus timing register 0 A-15
BRP5-BRP0 – baud rate prescalar bits A-16
SJW1, SJW0 – synchronization jump width bits A-15
CBT1 – MCAN bus timing register 1 A-17
SAMP – sampling bit A-17 D-29
,
,
B
,
B0ERR bit in STATH, STATL B-39
B1ERR bit in STATH, STATL B-38
biphase mode A-19
bit time calculation A-18
Bit timing 7-6
configuration, TOUCAN B-14
construction of 7-6 7-7
maximum bit rate 7-7
maximum oscillator tolerance 7-6
nominal bit rate 6-1 13-1
nominal bit time 6-1 13-1
PHASE SEG 13-2
PHASE SEG1 6-2 13-2
PHASE SEG2 6-2 13-2
PROP SEG 6-2 13-2
SYNC SEG 6-2 13-2
synchronization 6-3 13-4
time quantum 6-2 13-2
Bit-stream coding 3-13 10-17
block diagrams
MCAN interface A-5
,
,
,
,
,
,
,
,
,
CAN PROTOCOL
Rev. 3
,
,
,
,
,
,
,
,
,
,
INDEX
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
v
260
Freescale Semiconductor, Inc.
TSEG22-TSEG10 – time segment bits A-17
CBTR0 — MSCAN bus timing reg. C-27
BPR5 — BPR0 C-27
SJW1, SJW0 C-27
CBTR1 — MSCAN bus timing reg.
SAMP C-28
TSEG22 — TSEG10 C-28
CCNTRL – MCAN control register A-7 D-26 D-27
EIE – error interrupt enable bit A-8
MODE – undefined mode bit A-7
OIE – overrun interrupt enable bit A-8
RIE – receive interrupt enable bit A-8
RR – reset request bit A-8 D-26
SPD – speed mode bit A-8
TIE – transmit interrupt enable bit A-8
CCOM – MCAN command register A-9
AT – abort transmission bit A-11
COMPSEL – comparator selector bit A-10
COS – clear overrun status bit A-10
RRB – release receive buffer bit A-10
RX0, RX1 – receive pin bits A-9
SLEEP – go to sleep bit A-10 D-26
TR – transmission request bit A-11
CIDAC — MSCAN identifier acceptance control reg.
IDAM1 — IDAM0 C-35
IDHIT C-35
CIDAR0—3 — MSCAN08 identifier acceptance reg. C-37
AC7 — AC0 C-37
CIDMR0—3 — MSCAN08 identifier mask reg.
AM7 — AM0 C-38
CINT – MCAN interrupt register A-13 D-31 D-33 D-34
D-35 D-36 D-39 D-40
EIF – error interrupt flag A-13 D-31 D-32 D-33
OIF – overrun interrupt flag A-13 D-32 D-34
RIF – receive interrupt flag A-14 D-32
TIF – transmit interrupt flag A-14 D-34
WIF – wake-up interrupt flag A-13 D-31
CLKSRC bit in CMCR1 C-26
clock system
MSCAN08 C-16
CMCR0 — MSCAN module control reg.
SFTRES C-25
SLPAK C-25
SLPRQ C-25
SYNCH C-25
TLNKEN C-25
CMCR1 — MSCAN module control reg. C-26
CLKSRC C-26
LOOPB C-26
WUPM C-26
COCNTRL – MCAN output control register A-19
OCM1, OCM0 – output control mode bits A-19
compatibility
CAN protocols 7-10
COMPSEL bit in CCOM A-10
control registers
CBTR0 C-27
CBTR1 C-28
CIDAC C-35
CMCR0 C-25
Freescale Semiconductor, Inc...
,
,
,
,
,
MOTOROLA
vi
,
,
,
,
,
,
,
,
,
,
,
,
,
,
CMCR1 C-26
CRFLG C-29
CRIER C-31
CTCR C-34
CTFLG C-33
CTRL1 B-32
CTRL2 B-34
CTRLO B-31
PRESDIV B-34
TIMER B-35
COS bit in CCOM A-10
CPU
MSCAN08, wait mode C-15
CRC field
standard and extended formats 10-6
CRCER bit in STATH, STATL B-39
CRFLG — MSCAN receiver flag reg.
BOFFIF C-30
OVRIF C-30
RERRIF C-30
RWRNIF C-29
RXF C-31
TERRIF C-30
TWRNIF C-30
WUPIF C-29
CRIER — MSCAN receiver interrupt enable reg.
BOFFIE C-32
OVRIE C-32
RERRIE C-31
RWRNIE C-31
RXFIE C-32
TERRIE C-32
TWRNIE C-31
WUPIE C-31
CRXERR — MSCAN receive error counter C-36
CSTAT – MCAN status register A-11
BS – bus status bit A-11
DO – data overrun bit A-12
ES – error status bit A-11
RBS – receive buffer status bit A-13
RS – receive status bit A-12
TBA – transmit buffer access bit A-12
TCS – transmission complete status bit A-12
TS – transmit status bit A-12
CTCR — MSCAN transmitter control reg.
ABTRQ2 — ABTRQ0 C-34
TXEIE2 — TXEIE0 C-34
CTFLG — MSCAN transmitter flag reg. C-33
ABTAK2 — ABTAK0 C-33
TXE2 — TXE0 C-33
CTRL0 — TOUCAN control reg. 0
BOFF B-31
ERR B-31
RXMD[1,0] B-31
TXMD[1,0] B-32
CTRL1 — TOUCAN control reg. 1
LBUF B-33
PSEG[2:0] B-33
SAMP B-32
TSYNC B-32
INDEX
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
261
Freescale Semiconductor, Inc.
CTRL2 — TOUCAN control reg. 2
PSEG1[2:0] B-34
PSEG2[2:0] B-34
RJW[1:0] B-34
CTXERR — MSCAN transmit error counter C-36
F
D
,
Freescale Semiconductor, Inc...
ES bit in CSTAT A-11
external pins
MSCAN08 C-3
TOUCAN B-3
data frame 3-2 10-2
ACK field 3-5 10-7
arbitration field 3-2 10-3
control field 3-3 10-4
CRC field 3-4 10-6 10-6
data field 3-3 10-5
start of frame 10-2
data link layer
logical link control (LLC) sublayer 8-1
medium access control (MAC) sublayer 8-1
DB7-DB0 bits in TDS A-23
DEBUG mode
TOUCAN B-16
DLC3 — DLC0 bits in DLR C-22
DLC3-DLC0 bits in TRTDL A-22 D-23
DLR — MSCAN08 data length reg.
DLC3 — DLCO C-22
DO bit in CSTAT A-12
DSRn — MSCAN08 data segment reg. C-23
,
,
,
,
,
,
,
E
FMERR bit in STATH, STATL B-39
frame, formats of 3-1 10-1
CAN frame extended format 10-16
CAN frame standard format 10-14
CAN frames 3-11
conformance 10-13
data frame 3-2 10-2 10-2
error frame 3-7 3-7 10-8 10-9
interframe space 3-9
overload frame 3-8 3-8 10-10 10-10 B-13
remote frame 3-6 3-6 10-8 10-8 B-12
TOUCAN B-5
FRZ0 bit 0 in MCR B-26
FRZ1 bit 1 in MCR B-26
FRZAK bit in MCR B-27
,
,
,
,
,
,
,
,
,
,
,
,
,
,
G
global information registers, STATH, STATL B-38
H
EIE bit in CCNTRL A-8
EIF bit in CINT A-13 D-31 D-32 D-33
ERR bit in CTRL0 B-31
ERRINT bit in STATH, STATL B-40
error counters
TOUCAN B-42
error counts 5-1 12-1
exception 1 5-2 12-2
exception 2 5-2 12-2
error detection
CRC 2-5 9-5
monitoring 2-5 9-5
error frame 3-7 10-8
error delimiter 3-8 10-9
error flag 3-7 10-9
errors 4-1 11-1
acknowledgement error 4-2 7-4 11-2
bit error 4-1 11-1
CRC error 4-1 11-1
error signalling 4-2 11-2
fault confinement 2-5 9-5
form error 4-2 11-2
local error, ERROR ACTIVE 7-2
local error, ERROR PASSIVE 7-5
recovery time 2-5 9-5
signalling 2-5 9-5
stuff error 4-1 11-1
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
CAN PROTOCOL
Rev. 3
,
,
,
HALT bit in MCR B-26
I
IAI[4:1] bits in MCR B-29
ICR — TOUCAN interrupt configuration reg.
ICR[4:0] B-30
IRQ[3:1] B-29
IVB[3:1] B-30
ICR[4:0] bits in ICR B-30
ID10-ID3 bits in TBI A-21
ID28 — ID19 B-36
ID2-ID0 bits in TRTDL A-22
IDAM1 — IDAM0 flags in CIDAC C-35
IDE bit in arbitration field, extended format 10-4
IDE bit in IDRn C-21
identifier acceptance filter
MSCAN08 C-8
identifier registers
MSCAN08 C-21
IDHIT — identifier acceptance hit indicator in CIDAC C-35
IDLE bit in STATH, STATL B-39
IDRn — MSCAN identifier reg. C-21
IDE C-21
RTR C-22
SRR C-21
INDEX
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
vii
262
Freescale Semiconductor, Inc.
IFLAGH, IFLAGL — TOUCAN interrupt flag reg.
IFLG[15:0] B-41
IFLG[15:0] bits in IFLAGH, IFLAGL B-42
IMASKH, IMASKL— TOUCAN interrupt mask reg.
IMSK[15:0] B-41
IMSK[15:0] bits in IMASKH, IMSAKL B-41
information processing time 6-2 13-2
interframe space 3-9 10-11
Bus idle 3-10 10-13
INTERMISSION 3-10 10-12
suspend transmission 10-13
interrupts
acknowledge, MSCAN08 C-11
MSCAN08 C-11
TOUCAN B-20
vectors, MSCAN08 C-12
IRQ[3:1] field in ICR B-29
IVB[3:1] bits in ICR B-30
Freescale Semiconductor, Inc...
,
,
,
,
L
LBUF bit in CTRL1 B-33
LOOPB bit in CMCR1 C-26
low power modes
auto power save mode B-18
MSCAN08 C-13
STOP mode, TOUCAN B-16
M
MCAN
biphase mode A-19
BSP — bit stream processor A-3
BTL — bit timing logic A-4
CIL — controller interface unit A-5
control registers A-7
EML — error management logic A-4
functional overview A-1
IML — interface management logic A-1
interface A-5
interface block diagram A-5
memory map A-6
module block diagram A-2
normal mode 1 A-20
normal mode 2 A-20
organization of buffers A-25
oscillator block diagram A-16
output control bits A-20
RBF — receive buffer A-3
TBF — transmit buffer A-3
TCL — transceive logic A-4
MCR — TOUCAN module configuration reg.
FRZ0 B-26
FRZ1 B-26
FRZAK B-27
HALT B-26
IAI[4:1] B-29
MOTOROLA
viii
NTRDY B-26
PWRSV B-28
SFTRST B-27
STOP B-25
STPAK B-29
SUPV B-28
SWAKE B-28
WKMSK B-27
memory map
MCAN A-6
MSCAN08 C-19
TOUCAN B-24
message
buffer handling, TOUCAN B-11
buffer outline, MSCAN08 C-20
buffer structure, TOUCAN B-4
storage, MSCAN08 C-20
transfer, Bit-stream coding 3-13
MODE bit in CCNTRL A-7
MSCAN08
clock system C-16
clocking scheme C-17
external pins C-3
identifier acceptance filter C-8
internal sleep mode C-13
interrupt vectors C-12
interrupts C-11
low power modes C-13
memory map C-19
message buffer organization C-6
power down mode C-15
programmable wake-up function C-15
protocol violation protection C-12
receive structures C-5
soft reset mode C-15
timer link C-16
transmit structures C-7
N
normal mode 1 A-20
normal mode 2 A-20
NTRDY bit in MCR B-26
O
object layer
LLC 8-1
OCM1, OCM0 bits in COCNTRL A-19
OIE bit in CCNTRL A-8
OIF bit in CINT A-13 D-32 D-34
oscillator tolerance 9-7
calculation of 7-8
for enhanced CAN protocol 7-9
for existing CAN protocol 7-9
maximum 7-9
protocol modifications 7-1
,
INDEX
,
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
263
Freescale Semiconductor, Inc.
,
overload frame 3-8 10-10
overload delimiter 3-9 10-11
overload flag 3-9 10-11
OVRIE bit in CRIER C-32
OVRIF flag in CRFLG C-30
,
,
P
Freescale Semiconductor, Inc...
,
Phase-Buffer-Segments 6-2 13-2
pins
Rx0 B-3
Tx0 B-3
Tx1 B-3
prescaler C-27
PRESDIV — TOUCAN prescaler divide reg.
PRESDIV[15:8] B-34
PRESDIV[15:8] bits in PRESDIV B-34
PRIO7 — PRIO0 bits in TBPR C-23
PSEG[2:0] bits in CTRL1 B-33
PSEG1[2:0] bits in CTRL2 B-34
PSEG2[2:0] bits in CTRL2 B-34
PWRSV bit in MCR B-28
R
RBI – receive buffer identifier register A-23
RBS bit in CSTAT A-13
RDS – receive data segment registers A-23
receiver, definition of 3-1
remote data request 2-3 9-3
remote frame 3-6 10-8
RERRIE bit in CRIER C-31
RERRIF flag in CRFLG C-30
RIE bit in CCNTRL A-8
RIF bit in CINT A-14 D-32
RJW[1:0] bits in CTRL2 B-34
RR bit in CCNTRL A-8 D-26
RRB bit in CCOM A-10
RRTDL – transmission request/DLC register A-23
RS bit in CSTAT A-12
RTR bit in arbitration field 3-3
standard and extended formats 10-4
RTR bit in IDRn C-22
RTR bit in TRTDL A-22 D-22
RWRNIE bit in CRIER C-31
RWRNIF flag in CRFLG C-29
Rx mask reg. B-35
RX0, RX1 bits in CCOM A-9
RXF flag in CRFLG C-31
RXFIE bit in CRIER C-32
RXMASK — TOUCAN Rx global mask reg.
Base ID B-36
RXMD[1,0] bits in CTRL0 B-31
RXWRN bit in STATH, STATL B-39
,
,
,
,
,
S
,
SAMP bit in CBT1 A-17 D-29
SAMP bit in CBTR1 C-28
SAMP bit in CTRL1 B-32
SFTRES bit in CMCR0 C-25
SFTRST bit in MCR B-27
SJW1, SJW0 — synchronization jump width in CBTR0
C-27
SJW1, SJW0 bits in CBT0 A-15
SLEEP bit in CCOM A-10 D-26
sleep mode/wake-up, CAN protocol 2-6 9-6
SLPAK bit in CMCR0 C-25
SLPRQ bit in CMCR0 C-25
SPD bit in CCNTRL A-8
SRR bit in arbitration field, extended format 10-4
SRR bit in IDRn C-21
STATH, STATL — TOUCAN error and status report reg.
B-38
ACKER B-39
B0ERR B-39
B0FINT B-40
B1ERR B-38
BUS_STATE B-40
CRCER B-39
ERRINT B-40
FMERR B-39
IDLE B-39
RXWRN B-39
STERR B-39
TX/RX B-39
TXWRN B-39
WKINT B-40
STERR bit in STATH, STATL B-39
STOP bit in MCR B-25
STOP mode
TOUCAN B-16
STPAK bit in MCR B-29
SUPV bit in MCR B-28
SWAKE bit in MCR B-28
SYNCH bit in CMCR0 C-25
synchronization 6-3 13-4
hard 6-3 13-4
phase error of an edge 6-4 13-4
resynchronization 6-4 13-4
resynchronization jump width 6-3 13-4
rules of 6-4 13-5
system clock
TOUCAN B-14
system registers B-25
ICR B-29
MCR B-25
TCR B-29
,
,
,
,
,
,
,
,
T
TBA bit in CSTAT A-12
TBI – transmit buffer identifier register A-21
CAN PROTOCOL
Rev. 3
INDEX
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
ix
264
Freescale Semiconductor, Inc...
Freescale Semiconductor, Inc.
ID10-ID3 – identifier bits A-21
TBPR — transmit buffer priority reg.
C-23
PRIO7 — PRIO0 C-23
TCR — TOUCAN test configuration reg. B-29
TCS bit in CSTAT A-12
TDS – transmit data segment registers A-23
DB7-DB0 – data bits A-23
TERRIE bit in CRIER C-32
TERRIF flag in CRFLG C-30
TIE bit in CCNTRL A-8
TIF bit in CINT A-14 D-34
time quantum 6-2 13-2
time segments, length of 6-3 13-3
TIMER — TOUCAN free running timer B-35
timer link
MSCAN08 C-16
TLNKEN bit in CMCR0 C-25
TOUCAN
block diagram and pinout B-2
control registers B-31
extended format B-7
external Pins B-3
functional overview B-8
IDE B-7
interrupts B-20
lock/release/BUSY mechanism B-12
memory map B-24
message buffer handling B-11
message buffer structure B-4 B-4
module B-1
overload frames B-13
programmer’s model B-23
programming validity B-25
receive process B-10
remote frames B-12
RTR bit B-7 B-8
RTR/SRR bit treatment B-8
SMB usage B-12
special operating modes B-16
SRR bit B-7
standard format B-8
system registers B-25
TIME STAMP, extended format B-7
TIME STAMP, standard format B-8
transmit process B-9
TR bit in CCOM A-11
transfer layer, MAC sublayer 8-1
transmitter, definition of 3-1
TRTDL – transmission request/DLC register A-22
DLC3-DLC0 – data length code bits A-22 D-23
ID2-ID0 – identifier bits A-22
RTR – remote transmission request A-22 D-22
TS bit in CSTAT A-12
TSEG22 — TSEG10 — time segment in CBTR1 C-28
TSEG22-TSEG10 bits in CBT1 A-17
TSYNC bit in CTRL1 B-32
TWRNIE bit in CRIER C-31
TWRNIF flag in CRFLG C-30
TX/RX bit in STATH, STATL B-39
,
,
,
TXE2 — TXE0 flag in CTFLG C-33
TXEIE2 — TXEIE0 bit in CTCR C-34
TXMD[1,0] bits in CTRL0 B-32
TXWRN bit in STATH, STATL B-39
W
,
WIF bit in CINT A-13 D-31
WKINT bit in STATH, STATL B-40
WKMSK bit in MCR B-27
WUPIE bit in CRIER C-31
WUPIF flag in CRFLG C-29
WUPM bit in CMCR1 C-26
,
,
,
,
MOTOROLA
x
INDEX
For More Information On This Product,
Go to: www.freescale.com
CAN PROTOCOL
Rev. 3
265
Freescale Semiconductor, Inc.
CUSTOMER FEEDBACK QUESTIONNAIRE (CAN PROTOCOL)
Motorola wishes to continue to improve the quality of its documentation. We would welcome your feedback on the publication you
have just received. Having used the document, please complete this card (or a photocopy of it, if you prefer).
1.
How would you rate the quality of the document? Check one box in each category.
Excellent
Organization
Readability
Understandability
Illustrations
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
Excellent
❏
❏
❏
❏
❏
Tables
Table of contents
Index
Page size/binding
Overall impression
Poor
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
Comments:
2.
What is your intended use for this document? If more than one option applies, please rank them (1, 2, 3).
Selection of device for new application
System design
Training purposes
3.
❏
❏
❏
Other
❏
Please specify:
How well does this manual enable you to perform the task(s) outlined in question 2?
Completely
– Cut along this line to remove –
Freescale Semiconductor, Inc...
Accuracy
❏
❏
❏
❏
❏
Poor
Not at all
Comments:
❏ ❏ ❏ ❏
4.
How easy is it to find the information you are looking for?
Easy
Difficult
Comments:
❏ ❏ ❏ ❏
5.
Is the level of technical detail in the following sections sufficient to allow you to understand how the device functions?
Too little detail
SECTION 1
INTRODUCTION
SECTION 2
BASIC CONCEPTS
SECTION 3
MESSAGE TRANSFER
SECTION 4
ERROR HANDLING
SECTION 5
FAULT CONFINEMENT
SECTION 6
BIT TIMING REQUIREMENTS
SECTION 7
INCREASING OSCILLATOR TOLERANCE
SECTION 8
THE PHYSICAL LAYER
SECTION 9
INTRODUCTION
SECTION 10 BASIC CONCEPTS
SECTION 11 MESSAGE TRANSFER
SECTION 12 ERROR HANDLING
SECTION 13 FAULT CONFINEMENT
SECTION A
THE MOTOROLA CAN (MCAN) MODULE
SECTION B
TOUCAN
SECTION C
THE MOTOROLA SCALEABLE CAN (MSCAN08) MODULE
SECTION D
THE MOTOROLA SCALEABLE CAN (MSCAN12) MODULE
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
6.
Have you found any errors? If so, please comment:
7.
From your point of view, is anything missing from the document? If so, please say what:
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
Too much detail
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
TPG
For More Information On This Product,
Go to: www.freescale.com
266
8.
How could we improve this document?
9.
How would you rate Motorola’s documentation?
Excellent
– In general
– Against other semiconductor suppliers
✂
Freescale Semiconductor, Inc.
Poor
❏ ❏ ❏ ❏
❏ ❏ ❏ ❏
11. Which company (in any field) provides the best technical documentation?
12. How many years have you worked with microprocessors?
Less than 1 year
❏
1–3 years
❏
3–5 years
❏
More than 5 years
❏
– Second fold back along this line –
NE PAS AFFRANCHIR
By air mail
Par avion
NO STAMP REQUIRED
REPONSE PAYEE
GRANDE-BRETAGNE
Motorola Ltd.,
Colvilles Road,
Kelvin Industrial Estate,
EAST KILBRIDE,
G75 8BR.
GREAT BRITAIN.
– Cut along this line to remove –
IBRS NUMBER PHQ-B/207/G
CCRI NUMERO PHQ-B/207/G
– First fold back along this line –
Freescale Semiconductor, Inc...
10. Which semiconductor manufacturer provides the best technical documentation?
F.A.O. Technical Publications Manager
(re: BCANPSV2.0/D)
Semiconductor Products Sector
– Third fold back along this line –
13. Currently there is some discussion in the semiconductor industry regarding a move towards providing data sheets in electronic
form. If you have any opinion on this subject, please comment.
14. We would be grateful if you would supply the following information (at your discretion), or attach your card.
Name:
Phone No:
Position:
FAX No:
Department:
Company:
Address:
Thank you for helping us improve our documentation,
Technical Publications Manager, Motorola Ltd., Scotland.
TPG
For More Information On This Product,
Go
to: tuck
www.freescale.com
– Finally,
this edge into opposite flap –
267
Freescale Semiconductor, Inc.
INTRODUCTION
BASIC CONCEPTS
MESSAGE TRANSFER
Freescale Semiconductor, Inc...
ERROR HANDLING
FAULT CONFINEMENT
BIT TIMING REQUIREMENTS
INCREASING OSCILLATOR TOLERANCE
INTRODUCTION
BASIC CONCEPTS
MESSAGE TRANSFER
ERROR HANDLING
FAULT CONFINEMENT
BIT TIMING REQUIREMENTS
THE MOTOROLA CAN (MCAN) MODULE
TOUCAN
THE MOTOROLA SCALEABLE CAN (MSCAN08) MODULE
THE MOTOROLA SCALEABLE CAN (MSCAN12) MODULE
1
2
3
4
5
6
7
8
9
10
11
12
13
A
B
C
D
TPG
For More Information On This Product,
Go to: www.freescale.com
268
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc...
1
2
3
4
5
6
7
8
9
10
11
12
13
A
B
C
D
INTRODUCTION
BASIC CONCEPTS
MESSAGE TRANSFER
ERROR HANDLING
FAULT CONFINEMENT
BIT TIMING REQUIREMENTS
INCREASING OSCILLATOR TOLERANCE
INTRODUCTION
BASIC CONCEPTS
MESSAGE TRANSFER
ERROR HANDLING
FAULT CONFINEMENT
BIT TIMING REQUIREMENTS
THE MOTOROLA CAN (MCAN) MODULE
TOUCAN
THE MOTOROLA SCALEABLE CAN (MSCAN08) MODULE
THE MOTOROLA SCALEABLE CAN (MSCAN12) MODULE
TPG
For More Information On This Product,
Go to: www.freescale.com
269
Freescale Semiconductor, Inc.
1
2
3
Freescale Semiconductor, Inc...
4
5
6
7
8
9
10
11
12
13
14
For More Information On This Product,
Go to: www.freescale.com
15
1
Freescale Semiconductor, Inc.
2
3
Freescale Semiconductor, Inc...
4
5
6
7
8
9
10
11
12
13
14
How to reach us:
Mfax: [email protected] – TOUCHTONE 1-602-244-6609
US & CANADA ONLY: http://sps.motorola.com/mfax
INTERNET: SPS home-http://motorola.com/sps
USA/EUROPE: Motorola Literature Distribution; P.O. Box 5405; Denver, Colorado 80217. 1-303-675-2140
JAPAN: Nippon Motorola Ltd.; Tatsumi-SPD-JLDC, Toshikatsu Otsuki, 6F Seibu-Butsuryu-Center,
3-14-2 Tatsumi Koto-Ku, Tokyo 135, Japan. 03-3521-8315
HONG KONG: Motorola Semiconductors H.K. Ltd.; 8B Tai Ping Industrial Park, 51 Ting Kok Road,
Tai Po, N.T., Hong Kong. 852-26629298
15 !MOTOROLA
For More Information On This Product,
Go to: www.freescale.com