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DBC - CAN Database File

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What is a DBC file?

The files with .dbc extension are also known as CAN database files. The DBC file is a simple text file that consists of information for decoding raw CAN bus data to physical values or in human readable form. The DBC file is introduced, because this is the very common way to manage identification and translation of the data. The DBC file type was developed to provide the means of record keeping as described in a CAN network.

DBC File Format

DBC file format only represent the reading or passive part, it doesn’t provide a means to elaborate transmissions. To support vehicles that don’t have a specific native adaption yet. This is done using the general DBC vehicle type to use DBC files to translate CAN data into metrics. Each message in a DBC becomes a C structure with the signals being the members of the C structure.

DBC structure

The DBC data consists of the following elements:

Simple DBC Message

A simple DBC message consists of the Message ID, and at least one signal. Following is a demonstration of a message that consists of a single 8-bit signal.

BO_ 500 IO_DEBUG: 4 IO
 SG_ IO_DEBUG_test_unsigned : 0|8@1+ (1,0) [0|0] "" DBG

Signed signals

A signed signal can be sent by applying a negative offset to a signal. Following is an example of signed signal to the previous message.

BO_ 500 IO_DEBUG: 4 IO
 SG_ IO_DEBUG_test_unsigned : 0|8@1+ (1,0) [0|0] "" DBG
 SG_ IO_DEBUG_test_signed : 8|8@1- (1,-128) [0|0] "" DBG

Fractional Signals

A fractional signal can be sent by deciding the range, and the precision if required.

BO_ 500 IO_DEBUG: 4 IO
 SG_ IO_DEBUG_test_unsigned : 0|8@1+ (1,0) [0|0] "" DBG
 SG_ IO_DEBUG_test_signed : 8|8@1- (1,-128) [0|0] "" DBG
 SG_ IO_DEBUG_test_float1 : 16|8@1+ (0.1,0) [0|0] "" DBG
 SG_ IO_DEBUG_test_float2 : 24|12@1+ (0.01,-20.48) [-20.48|20.47] "" DBG

Enumeration Types

An enumeration type is used when the user wants to see names, instead of numbers. See the following example.

BO_ 500 IO_DEBUG: 4 IO
 SG_ IO_DEBUG_test_enum : 8|8@1+ (1,0) [0|0] "" DBG

BA_ "FieldType" SG_ 500 IO_DEBUG_test_enum "IO_DEBUG_test_enum";

VAL_ 500 IO_DEBUG_test_enum 2 "IO_DEBUG_test2_enum_two" 1 "IO_DEBUG_test2_enum_one" ;

Multiplexed Message

defining a multiplexed messages that uses a single message ID is an option, however, they are decoded differently depending on which multipexed value was sent. In order to send a multiplexed message below, a separate message have to be sent:

BO_ 200 SENSOR_SONARS: 8 SENSOR
 SG_ SENSOR_SONARS_mux M : 0|4@1+ (1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_err_count : 4|12@1+ (1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_left m0 : 16|12@1+ (0.1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_middle m0 : 28|12@1+ (0.1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_right m0 : 40|12@1+ (0.1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_rear m0 : 52|12@1+ (0.1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_no_filt_left m1 : 16|12@1+ (0.1,0) [0|0] "" DBG
 SG_ SENSOR_SONARS_no_filt_middle m1 : 28|12@1+ (0.1,0) [0|0] "" DBG
 SG_ SENSOR_SONARS_no_filt_right m1 : 40|12@1+ (0.1,0) [0|0] "" DBG
 SG_ SENSOR_SONARS_no_filt_rear m1 : 52|12@1+ (0.1,0) [0|0] "" DBG

DBC Example

Here is a complete example of a dbc file:

VERSION ""

NS_ :
	BA_
	BA_DEF_
	BA_DEF_DEF_
	BA_DEF_DEF_REL_
	BA_DEF_REL_
	BA_DEF_SGTYPE_
	BA_REL_
	BA_SGTYPE_
	BO_TX_BU_
	BU_BO_REL_
	BU_EV_REL_
	BU_SG_REL_
	CAT_
	CAT_DEF_
	CM_
	ENVVAR_DATA_
	EV_DATA_
	FILTER
	NS_DESC_
	SGTYPE_
	SGTYPE_VAL_
	SG_MUL_VAL_
	SIGTYPE_VALTYPE_
	SIG_GROUP_
	SIG_TYPE_REF_
	SIG_VALTYPE_
	VAL_
	VAL_TABLE_

BS_:

BU_: DBG DRIVER IO MOTOR SENSOR


BO_ 100 DRIVER_HEARTBEAT: 1 DRIVER
 SG_ DRIVER_HEARTBEAT_cmd : 0|8@1+ (1,0) [0|0] "" SENSOR,MOTOR

BO_ 500 IO_DEBUG: 4 IO
 SG_ IO_DEBUG_test_unsigned : 0|8@1+ (1,0) [0|0] "" DBG
 SG_ IO_DEBUG_test_enum : 8|8@1+ (1,0) [0|0] "" DBG
 SG_ IO_DEBUG_test_signed : 16|8@1- (1,0) [0|0] "" DBG
 SG_ IO_DEBUG_test_float : 24|8@1+ (0.5,0) [0|0] "" DBG

BO_ 101 MOTOR_CMD: 1 DRIVER
 SG_ MOTOR_CMD_steer : 0|4@1- (1,-5) [-5|5] "" MOTOR
 SG_ MOTOR_CMD_drive : 4|4@1+ (1,0) [0|9] "" MOTOR

BO_ 400 MOTOR_STATUS: 3 MOTOR
 SG_ MOTOR_STATUS_wheel_error : 0|1@1+ (1,0) [0|0] "" DRIVER,IO
 SG_ MOTOR_STATUS_speed_kph : 8|16@1+ (0.001,0) [0|0] "kph" DRIVER,IO

BO_ 200 SENSOR_SONARS: 8 SENSOR
 SG_ SENSOR_SONARS_mux M : 0|4@1+ (1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_err_count : 4|12@1+ (1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_left m0 : 16|12@1+ (0.1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_middle m0 : 28|12@1+ (0.1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_right m0 : 40|12@1+ (0.1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_rear m0 : 52|12@1+ (0.1,0) [0|0] "" DRIVER,IO
 SG_ SENSOR_SONARS_no_filt_left m1 : 16|12@1+ (0.1,0) [0|0] "" DBG
 SG_ SENSOR_SONARS_no_filt_middle m1 : 28|12@1+ (0.1,0) [0|0] "" DBG
 SG_ SENSOR_SONARS_no_filt_right m1 : 40|12@1+ (0.1,0) [0|0] "" DBG
 SG_ SENSOR_SONARS_no_filt_rear m1 : 52|12@1+ (0.1,0) [0|0] "" DBG




CM_ BU_ DRIVER "The driver controller driving the car";
CM_ BU_ MOTOR "The motor controller of the car";
CM_ BU_ SENSOR "The sensor controller of the car";
CM_ BO_ 100 "Sync message used to synchronize the controllers";

BA_DEF_ "BusType" STRING ;
BA_DEF_ BO_ "GenMsgCycleTime" INT 0 0;
BA_DEF_ SG_ "FieldType" STRING ;

BA_DEF_DEF_ "BusType" "CAN";
BA_DEF_DEF_ "FieldType" "";
BA_DEF_DEF_ "GenMsgCycleTime" 0;

BA_ "GenMsgCycleTime" BO_ 100 1000;
BA_ "GenMsgCycleTime" BO_ 500 100;
BA_ "GenMsgCycleTime" BO_ 101 100;
BA_ "GenMsgCycleTime" BO_ 400 100;
BA_ "GenMsgCycleTime" BO_ 200 100;
BA_ "FieldType" SG_ 100 DRIVER_HEARTBEAT_cmd "DRIVER_HEARTBEAT_cmd";
BA_ "FieldType" SG_ 500 IO_DEBUG_test_enum "IO_DEBUG_test_enum";


VAL_ 100 DRIVER_HEARTBEAT_cmd 2 "DRIVER_HEARTBEAT_cmd_REBOOT" 1 "DRIVER_HEARTBEAT_cmd_SYNC" 0 "DRIVER_HEARTBEAT_cmd_NOOP" ;
VAL_ 500 IO_DEBUG_test_enum 2 "IO_DEBUG_test2_enum_two" 1 "IO_DEBUG_test2_enum_one" ;

References

See also