SAE J1939 acquisition

1. Create nodes

(1) Open CommBridge Digital Twin and switch to Device Connectivity.

(2) Drag SAE J1939, Data Processing, and MQTT Upload into the workspace to create three nodes.

(3) Connect the three nodes in this order: SAE J1939 → Data Processing → MQTT Upload.

2. Create a scheme

(1) Double-click SAE J1939 and select Add scheme.

(2) Enter connection settings, import a DBC file, and select Next.

(3) Review group and point information.

(4) Select Finish to add the acquisition scheme.

(5) Enable the scheme and select Save.

3. View results

(1) Select Deploy under Device Connectivity and wait for success.

(2) Switch to Digital Twin and hover over SAE J1939 to display node information.

(3) Select a scheme to view real-time and historical point data in each group.

4. Configuration reference

Connection settings

Parameter	Prerequisite	Description	Format	Example	Notes
Scheme name		User-defined name for the scheme	Nonempty	CAN acquisition
CAN interface		Actual CAN interface on the device	Drop-down list	vcan0
DBC		See below	DBC file	testType.dbc
Name configuration method				Hex Number
Preferred address			Drop-down list	128
Returned data type		Type of acquired real-time data	Drop-down list	Phy
Socketcand		Whether to enable socketcand, which provides network access to the computer’s CAN interfaces	Yes, No	No
Socketcand port		Used for remote data debugging	Number
Name	Preferred address is Hex Number	A 64-bit (8-byte) Name that uniquely identifies each ECU		0x7758
Arbitrary address capable	Preferred address is Properties	Whether this ECU may automatically change its source address: 1 permits this, 0 fixes the address	Number: 0, 1	0
Industry group	Preferred address is Properties	Industry category of the vehicle	Number, range: [0,7]	0
Device class instance	Preferred address is Properties	Instance number distinguishing devices within the same class	Number, range: [0,15]	0
Device class	Preferred address is Properties	SAE-defined 7-bit device/system classification	Number, range: [0,127]	0
Function	Preferred address is Properties	Specific function performed by the ECU within the vehicle system	Number, range: [0,255]	0
Function instance	Preferred address is Properties	Instance number distinguishing multiple ECUs performing the same function	Number, range: [0,31]	0
ECU instance	Preferred address is Properties	Distinguishes instances of the same physical ECU model	Number, range: [0,7]	0
Manufacturer code	Preferred address is Properties	SAE-assigned 11-bit manufacturer identifier	Number, range: [0,2047]	0
Identity number	Preferred address is Properties	Manufacturer-defined 21-bit serial number	Number, range: [0,2097151]	0

Note:

1. DBC supplies the original data structure. Subsequent changes to groups (messages) and data (signals) are merged into this DBC structure.
2. Raw returns raw values; Phy returns physical values; PhyWIthUnit returns physical values with units.
3. Communication uses TCP/IP connections and a dedicated protocol to transmit CAN frames and control commands. Currently only Classical CAN is supported, not CAN FD.
4. Preferred address: Hex Number, Properties.
5. Two nodes on a J1939 network cannot use the same address. To avoid address conflicts, J1939 uses a 64-bit Name and an 8-bit Address together to identify a node. Name structure:
   1. Arbitrary address capable, 1 bit: 0 means the node’s address is statically configured by the network administrator; 1 means it is dynamically assigned at random.
   2. Industry group, 3 bits. Common values: 000 (global), 001 (on-highway vehicles, such as trucks and buses), 010 (agriculture), 011 (construction), etc.
   3. Vehicle system instance, 4 bits.
   4. Vehicle system, 7 bits.
   5. Reserved bit.
   6. Function, 8 bits.
   7. Function instance, 5 bits.
   8. ECU instance, 3 bits.
   9. Manufacturer code, 11 bits.
   10. Identity number, 21 bits.

Add groups

Parameter	Description	Format	Example
Group name	User-defined group name	Nonempty	t_msg_1_unsigned
Message name	Describes the message’s function or purpose	Nonempty; letters, digits, and underscores only; cannot start with a digit	t_msg_1_unsigned
Priority			3
Parameter group number			0x0
Data length code	Data length code (DLC): Classical CAN DLC 0–8 corresponds to 0–8 bytes. CAN FD DLC 0–8 also corresponds to 0–8 bytes; DLC 9–15 corresponds to 12, 16, 20, 24, 32, 48, and 64 bytes respectively. These protocol length definitions do not imply that the current plugin supports CAN FD.	Number, [0,8] or [0,15]	8
Transmitting node	Transmitter: the node sending the message	Dropdown, default Vector__XXX	Vector__XXX
Message description	Optional explanation of message function	String

Note:

1. A group corresponds to a Message in the DBC file.
2. If no transmitter is specified for the message (group), use Vector__XXX.

Add data

Parameter	Prerequisite	Description	Format	Example
Signal name		User-defined signal name describing its function
Suspect parameter number
Signal mode		Signal transmission mode	Dropdown
Start bit		Zero-based signal starting position within the CAN frame	Bits	0
Value type		Signal data type	Dropdown	Intel
Byte order		Signal storage order within the message	Dropdown
Scaling factor		Factor converting raw values to physical values	Floating-point number
Offset		Offset for physical value calculation	Floating-point number
Minimum		Minimum physical value limiting the signal range	Floating-point number
Maximum		Maximum physical value limiting the signal range	Floating-point number
Unit		Physical unit	String
Receiving nodes		One or more target nodes receiving the signal	Dropdown, default Vector__XXX
Description		Physical unit, such as km/h, °C, or m/s	String
Calculation		User-defined formula based on data aliases
Length	Value type is Unsigned/Signed	Number of bits occupied by the signal	Bits, [1,64]
Multiplex value	Signal mode is not Signal	Multiplexor value at which this signal becomes active

Note:

1. Signal modes: Signal, Multiplexor, Multiplexed.
2. Value types: Unsigned, Signed, Float (single precision), Double (double precision).
3. Byte order: Intel (little-endian) or Motorola (big-endian).
4. Start bit: position of the least significant bit (LSB).
5. End bit: position of the most significant bit (MSB).
6. Resolution and offset convert physical and network values: network value = (physical value - offset) ÷ resolution.
7. If no receiver is specified, use Vector__XXX.

5. DBC file parameter details

A DBC (CAN Database File) is a standard format describing messages and signals on a Controller Area Network bus.

Components

(1) Node

A node logically represents a network device and may transmit or receive messages.

1). DBC format:

BU_: Node1 Node2 Node3

• BU_: defines the node list.
• Node names follow, separated by spaces.

(2) Message

A message is the smallest transmitted data unit on the CAN network, containing multiple signals with a fixed ID and length.

1). DBC format:

BO_ <message-ID> <message-name>: <data-length-code> <transmitting-node>

2). Example:

BO_ 1001 SpeedMessage: 8 Node1

• BO_: identifies a message.
• 1001: message ID.
• SpeedMessage: message name.
• 8: data length code (DLC).
• Node1: transmitting node.

(3) Signal

A signal is a data unit within a message representing a physical quantity such as speed, rotational speed, or temperature.

1). DBC format:

SG_ <signal-name> : <start-bit>|<length>@<byte-order><value-type-sign> (<scaling-factor>,<offset>) [<minimum>|<maximum>] "<unit>" <receiving-node>

2). Example:

SG_ Speed : 0|16@1+ (0.1,0) [0|200] "km/h" Node2

• BO_: identifies a message.

Selected parameter explanations

1. d

63 (MSB)	62-60	59-56	55-49	48	47-40	39-35	34-32	31-21	20-0 (LSB)
Arbitrary address capable	Industry group	Vehicle system instance	Vehicle system	Reserved	Function	Function instance	ECU instance	Manufacturer code	Identity number
1 bit	3 bits	4 bits	7 bits	1 bit	8 bits	5 bits	3 bits	11 bits	21 bits

2. Signal modes

Signal mode	Meaning
Signal	Ordinary signal carrying data directly without special markers or relationships
Multiplexor	Selector signal determining which group of signals a message carries; for example, selects one of several data formats
Multiplexed	Signal bound to a multiplexor; the multiplexor value determines whether it is transmitted, such as a particular group sent when the selector equals 1