DBC_File_Format_Documentation
DBC File Format
Documentation
Version 01/2007
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? 2007 Vector Informatik GmbH
All rights reserved.
Document Management
Revision History
Version Editor Description
1.0 of 2007-02-09 Qu Specification created
Table of contents
1Introduction (1)
2General Definitions (1)
3Structure of the DBC File (2)
4Version and New Symbol Specification (3)
5Bit Timing Definition (3)
6Node Definitions (3)
7Value Table Definitions (3)
7.1Value Descriptions (Value Encodings) (4)
8Message Definitions (4)
8.1Signal Definitions (4)
8.2Definition of Message Transmitters (6)
8.3Signal Value Descriptions (Value Encodings) (6)
9Environment Variable Definitions (6)
9.1Environment Variable Value Descriptions (7)
10Signal Type and Signal Group Definitions (7)
11Comment Definitions (7)
12User Defined Attribute Definitions (8)
12.1Attribute Definitions (8)
12.2Attribute Values (8)
13Examples (8)
1 Introduction
The DBC file describes the communication of a single CAN network. This informa-tion is sufficient to monitor and analyze the network and to simulate nodes not physically available (remaining bus simulation).
The DBC file can also be used to develop the communication software of an elec-tronic control unit which shall be part of the CAN network. The functional behavior of the ECU is not addressed by the DBC file.
2 General Definitions
The following general elements are used in this documentation:
unsigned_integer: an unsigned integer
signed_integer: a signed integer
double: a double precision float number
char_string: an arbitrary string consisting of any printable charac-ters except double hyphens ('"').
C_identifier: a valid C_identifier. C_identifiers have to start with am alpha character or an underscore and may further consist of
alpha-numeric characters and underscores.
C_identifier = (alpha_char | '_') {alpha_num_char | '_'}
C-identifiers used in DBC files may have a length of up to 128 characters. To be compatible to older tools the length should not exceed 32 characters.
Other strings used in DBC files may be of an arbitrary length.
The keywords used in DBC files o identify the type of an object are given in the following table:
Keyword Object Type
BU_ Network Node
BO_ Message
SG_ Signal
EV_ Environment Variable
The syntax is described using the extended BNF notation (Backus-Naur-Format). Symbol Meaning
= A name on the left of the = is defined using the syntax on the right (syntax rule).
; The semicolon terminates a definition.
| The vertical bar indicates an alternative.
[ … ] The definitions within brackets are optional (zero or one occurrence).
{ … } The definitions within braces repeated (zero or multiple occurrences)
( … ) Parentheses define grouped elements.
' … ' Text in hyphens has to appear as defined.
(* … *) Comment.
3 Structure of the DBC File
The DBC file format has the following overall structure:
DBC_file =
version
new_symbols
bit_timing (*obsolete but required*)
nodes
value_tables
messages
message_transmitters
environment_variables
environment_variables_data
signal_types
comments
attribute_definitions
sigtype_attr_list
attribute_defaults
attribute_values
value_descriptions
category_definitions (*obsolete*)
categories (*obsolete*)
filter (*obsolete*)
signal_type_refs
signal_groups
signal_extended_value_type_list ;
DBC files describing the basic communication of a CAN network include the fol-lowing sections:
?Bit_timing
This section is required but is normally empty.
?nodes
This section is required and defines the network nodes.
?messages
This section defines the messages and the signals.
The following sections aren't used in normal DBC files. They are defined here for the sake of completeness only:
?signal_types
?sigtype_attr_list
?category_definitions
?categories
?filter
?signal_type_refs
?signal_extended_value_type_list
DBC files that describe the CAN communication and don't define any additional data for system or remaining bus simulations don't include environment variables.
4 Version and New Symbol Specification
The DBC files contain a header with the version and the new symbol entries. The version either is empty or is a string used by CANdb editor.
version = ['VERSION' '"' { CANdb_version_string } '"' ];
new_symbols = [ '_NS' ':' ['CM_'] ['BA_DEF_'] ['BA_'] ['VAL_'] ['CAT_DEF_'] ['CAT_'] ['FILTER'] ['BA_DEF_DEF_'] ['EV_DATA_']
['ENVVAR_DATA_'] ['SGTYPE_'] ['SGTYPE_VAL_'] ['BA_DEF_SGTYPE_']
['BA_SGTYPE_'] ['SIG_TYPE_REF_'] ['VAL_TABLE_'] ['SIG_GROUP_']
['SIG_VALTYPE_'] ['SIGTYPE_VALTYPE_'] ['BO_TX_BU_']
['BA_DEF_REL_'] ['BA_REL_'] ['BA_DEF_DEF_REL_'] ['BU_SG_REL_']
['BU_EV_REL_'] ['BU_BO_REL_'] ];
5 Bit Timing Definition
The bit timing section defines the baudrate and the settings of the BTR registers of the network This section is obsolete and not used any more. Nevertheless he keyword 'BS_' must appear in the DBC file.
bit_timing = 'BS_:' [baudrate ':' BTR1 ',' BTR2 ] ;
baudrate = unsigned_integer ;
BTR1 = unsigned_integer ;
BTR2 = unsigned_integer ;
6 Node Definitions
The node section defines the names of all participating nodes The names defined in this section have to be unique within this section.
nodes = 'BU_:' {node_name} ;
node_name = C_identifier ;
7 Value Table Definitions
The value table section defines the global value tables. The value descriptions in value tables define value encodings for signal raw values. In commonly used DBC files the global value tables aren't used, but the value descriptions are defined for each signal independently.
value_tables = {value_table} ;
value_table = 'VAL_TABLE_' value_table_name {value_description} ';' ;
value_table_name = C_identifier ;
7.1 Value Descriptions (Value Encodings)
A value description defines a textual description for a single value. This value may either be a signal raw value transferred on the bus or the value of an environment variable in a remaining bus simulation.
value_description = double char_string ;
8 Message Definitions
The message section defines the names of all frames in the cluster as well as their properties and the signals transferred on the frames.
messages = {message} ;
message = BO_ message_id message_name ':' message_size trans-mitter {signal} ;
message_id = unsigned_integer ;
The message's CAN-ID. The CAN-ID has to be unique within the DBC file. If the most significant bit of the CAN-ID is set, the ID is an extended CAN ID. The ex-tended CAN ID can be determined by masking out the most significant bit with the mask 0xCFFFFFFF.
message_name = C_identifier ;
The names defined in this section have to be unique within the set of messages.
message_size = unsigned_integer ;
The message_size specifies the size of the message in bytes.
transmitter = node_name | 'Vector__XXX' ;
The transmitter name specifies the name of the node transmitting the message. The sender name has to be defined in the set of node names in the node section. If the massage shall have no sender, the string 'Vector__XXX' has to be given here.
8.1 Signal Definitions
The message's signal section lists all signals placed on the message, their position in the message's data field and their properties.
signal = 'SG_' signal_name multiplexer_indicator ':' start_bit '|' signal_size '@' byte_order value_type '(' factor ',' offset ')'
'[' minimum '|' maximum ']' unit receiver {',' receiver} ;
signal_name = C_identifier ;
The names defined here have to be unique for the signals of a single message.
multiplexer_indicator = ' ' | 'M' | m multiplexer_switch_value ; The multiplexer indicator defines whether the signal is a normal signal, a multi-plexer switch for multiplexed signals, or a multiplexed signal. A 'M' (uppercase) character defines the signal as the multiplexer switch. Only one signal within a single message can be the multiplexer switch. A 'm' (lowercase) character followed by an unsigned integer defines the signal as being multiplexed by the multiplexer switch. The multiplexed signal is transferred in the message if the switch value of the multiplexer signal is equal to its multiplexer_switch_value.
start_bit = unsigned_integer ;
The start_bit value specifies the position of the signal within the data field of the frame. For signals with byte order Intel (little endian) the position of the least-significant bit is given. For signals with byte order Motorola (big endian) the posi-tion of the most significant bit is given. The bits are counted in a sawtooth manner. The startbit has to be in the range of 0 to (8 * message_size - 1).
signal_size = unsigned_integer ;
The signal_size specifies the size of the signal in bits
byte_order = '0' | '1' ; (* 0=little endian, 1=big endian *)
The byte_format is 0 if the signal's byte order is Intel (little endian) or 1 if the byte order is Motorola (big endian).
value_type = '+' | '-' ; (* +=unsigned, -=signed *)
The value_type defines the signal as being of type unsigned (-) or signed (-).
factor = double ;
offset = double ;
The factor and offset define the linear conversion rule to convert the signals raw value into the signal's physical value and vice versa:
physical_value = raw_value * factor + offset
raw_value = (physical_value – offset) / factor
As can be seen in the conversion rule formulas the factor must not be 0.
minimum = double ;
maximum = double ;
The minimum and maximum define the range of valid physical values of the signal.
unit = char_string ;
receiver = node_name | 'Vector__XXX' ;
The receiver name specifies the receiver of the signal. The receiver name has to be defined in the set of node names in the node section. If the signal shall have no receiver, the string 'Vector__XXX' has to be given here.
Signals with value types 'float' and 'double' have additional entries in the sig-
nal_valtype_list section.
signal_extended_value_type_list = 'SIG_VALTYPE_' message_id sig-nal_name signal_extended_value_type ';' ;
signal_extended_value_type = '0' | '1' | '2' | '3' ; (* 0=signed or unsigned integer, 1=32-bit IEEE-float, 2=64-bit IEEE-double *)
8.2 Definition of Message Transmitters
The message transmitter section enables the definition of multiple transmitter nodes of a single node. This is used to describe communication data for higher-layer protocols. This is not used to define CAN layer-2 communication.
message_transmitters = {message_transmitter} ;
Message_transmitter = 'BO_TX_BU_' message_id ':' {transmitter} ';' ;
8.3 Signal Value Descriptions (Value Encodings)
Signal value descriptions define encodings for specific signal raw values.
value_descriptions = { value_descriptions_for_signal |
value_descriptions_for_env_var } ;
value_descriptions_for_signal = 'VAL_' message_id signal_name { value_description } ';' ;
9 Environment Variable Definitions
In the environment variables section the environment variables for the usage in system simulation and remaining bus simulation tools are defined.
environment_variables = {environment_variable}
environment_variable = 'EV_' env_var_name ':' env_var_type '[' mini-mum '|' maximum ']' unit initial_value ev_id access_type ac-
cess_node {',' access_node } ';' ;
env_var_name = C_identifier ;
env_var_type = '0' | '1' | '2' ; (* 0=integer, 1=float, 2=string *) minimum = double ;
maximum = double ;
initial_value = double ;
ev_id = unsigned_integer ; (* obsolete *)
access_type = 'DUMMY_NODE_VECTOR0' | 'DUMMY_NODE_VECTOR1' |
'DUMMY_NODE_VECTOR2' | 'DUMMY_NODE_VECTOR3' ; (*
0=unrestricted, 1=read, 2=write, 3=readWrite *)
access_node = node_name | 'VECTOR_XXX' ;
The entries in the environment variables data section define the environments listed here as being of the data type "Data". Environment variables of this type can store an arbitrary binary data of the given length. The length is given in bytes.
environment_variables_data = environment_variable_data ;
environment_variable_data = 'ENVVAR_DATA_' env_var_name ':'
data_size ';' ;
data_size = unsigned_integer ;
9.1 Environment Variable Value Descriptions
The value descriptions for environment variables provide textual representations of specific values of the variable.
value_descriptions_for_env_var = 'VAL_' env_var_aname
{ value_description } ';' ;
10 Signal Type and Signal Group Definitions
Signal types are used to define the common properties of several signals. They are normally not used in DBC files.
signal_types = {signal_type} ;
signal_type = 'SGTYPE_' signal_type_name ':' signal_size '@' byte_order value_type '(' factor ',' offset ')' '[' minimum '|'
maximum ']' unit default_value ',' value_table ';' ;
signal_type_name = C_identifier ;
default_value = double ;
value_table = value_table_name ;
signal_type_refs = {signal_type_ref} ;
signal_type_ref = 'SGTYPE_' message_id signal_name ':' sig-
nal_type_name ';' ;
Signal groups are used to define a group of signals within a messages, e.g. to de-fine that the signals of a group have to be updated in common.
signal_groups = 'SIG_GROUP_' message_id signal_group_name repeti-tions ':' { signal_name } ';' ;
signal_group_name = C_identifier ;
repetitions = unsigned_integer ;
11 Comment Definitions
The comment section contains the object comments. For each object having a comment, an entry with the object's type identification is defined in this section.
comments = {comment} ;
comment = 'CM_' (char_string |
'BU_' node_name char_string |
'BO_' message_id char_string |
'SG_' message_id signal_name char_string |
'EV_' env_var_name char_string)
';' ;
12 User Defined Attribute Definitions
User defined attributes are a means to extend the object properties of the DBC file. These additional attributes have to be defined using an attribute definition with an attribute default value. For each object having a value defined for the attribute an attribute value entry has to be defined. If no attribute value entry is defined for an object the value of the object's attribute is the attribute's default.
12.1 Attribute Definitions
attribute_definitions = { attribute_definition } ;
attribute_definition = 'BA_DEF_' object_type attribute_name attrib-ute_value_type ';' ;
object_type = '' | 'BU_' | 'BO_' | 'SG_' | 'EV_' ;
attribute_name = '"' C_identifier '"' ;
attribute_value_type = 'INT' signed_integer signed_integer | 'HEX' signed_integer signed_integer |
'FLOAT' double double |
'STRING' |
'ENUM' [char_string {',' char_string}]
attribute_defaults = { attribute_default } ;
attribute_default = 'BA_DEF_DEF_' attribute_name attribute_value ';' ;
attribute_value = unsigned_integer | signed_integer | double | char_string ;
12.2 Attribute Values
attribute_values = { attribute_value_for_object } ;
attribute_value_for_object = 'BA_' attribute_name (attribute_value | 'BU_' node_name attribute_value |
'BO_' message_id attribute_value |
'SG_' message_id signal_name attribute_value |
'EV_' env_var_name attribute_value)
';' ;
13 Examples
VERSION ""
NS_ :
NS_DESC_
CM_
BA_DEF_
BA_
VAL_
CAT_DEF_
CAT_
FILTER
BA_DEF_DEF_
EV_DATA_
ENVVAR_DATA_
SGTYPE_
SGTYPE_VAL_
BA_DEF_SGTYPE_
BA_SGTYPE_
SIG_TYPE_REF_
VAL_TABLE_
SIG_GROUP_
SIG_VALTYPE_
SIGTYPE_VALTYPE_
BO_TX_BU_
BA_DEF_REL_
BA_REL_
BA_DEF_DEF_REL_
BU_SG_REL_
BU_EV_REL_
BU_BO_REL_
BS_:
BU_: Engine Gateway
BO_ 100 EngineData: 8 Engine
SG_ PetrolLevel : 24|8@1+ (1,0) [0|255] "l" Gateway
SG_ EngPower : 48|16@1+ (0.01,0) [0|150] "kW" Gateway
SG_ EngForce : 32|16@1+ (1,0) [0|0] "N" Gateway
SG_ IdleRunning : 23|1@1+ (1,0) [0|0] "" Gateway
SG_ EngTemp : 16|7@1+ (2,-50) [-50|150] "degC" Gateway SG_ EngSpeed : 0|16@1+ (1,0) [0|8000] "rpm" Gateway
CM_ "CAN communication matrix for power train electronics ******************************************************* implemented: turn lights, warning lights, windows";
VAL_ 100 IdleRunning 0 "Running" 1 "Idle" ;