Analysis of J1939 to OBD2 Cable Principle

In the field of automotive electronic communication, J1939 and OBD2 are two important communication standards. J1939 is mainly used in commercial vehicles and engineering machinery, while OBD2 is widely used in passenger cars. The emergence of J1939 to OBD2 cables has enabled the connection between different communication standards, enabling devices based on different protocols to interconnect and communicate with each other. To understand its principle, it is necessary to first understand the differences between J1939 and OBD2 protocols.

Protocol differences

The J1939 protocol is a communication protocol based on the CAN (Controller Area Network) bus, which adopts a multi master communication mode and can simultaneously connect multiple electronic control units (ECUs). Its data frame structure is rich, including arbitration segment, control segment, data segment, CRC segment, ACK segment, and frame end segment. Through identifier arbitration mechanism, it avoids data conflicts and ensures efficient and accurate data transmission. The OBD2 protocol is also based on the CAN bus, but it differs significantly from J1939 in terms of data format, fault code definition, and communication methods. OBD2 is mainly used for vehicle fault diagnosis, with a relatively simple data frame format that focuses on the transmission of fault information and the reception of diagnostic instructions.

Conversion principle

The protocol conversion from J1939 to OBD2 cable relies on the collaborative work of hardware and software. In terms of hardware, the core is the protocol conversion chip, which has two communication interfaces connected to the physical layers of J1939 and OBD2, respectively. When the J1939 interface receives data, the conversion chip first parses the data frame, identifies the identifiers, data content, and other information within it. The software part is responsible for running the protocol conversion algorithm, extracting information from J1939 data frames according to pre programmed rules, and repackaging it according to the data format of the OBD2 protocol. For example, the representation and storage location of engine speed data in the J1939 protocol are different from those in OBD2. Software algorithms will extract the engine speed data in J1939 and convert it into the format and data range specified in the OBD2 protocol.

When converting OBD2 data to J1939 data, the process is the opposite. The chip receives data from the OBD2 interface, and the software algorithm parses it to extract valid information. It then reorganizes the data frame according to the J1939 protocol format and sends it out through the J1939 interface.

Data integrity and accuracy assurance

To ensure the integrity and accuracy of the data during the conversion process, multiple measures have been taken for the J1939 to OBD2 cable. In terms of hardware, high-performance conversion chips and high-quality electronic components are selected to reduce interference and noise during signal transmission. In software algorithms, data verification and error correction mechanisms have been added to perform CRC and parity checks on the data before and after conversion. Once data errors are detected, they are promptly corrected or retransmitted.

The J1939 to OBD2 cable achieves efficient conversion between J1939 and OBD2 protocols through unique hardware and software design, providing convenience for fields such as automotive maintenance, inspection, and fleet management. With the development of automotive electronics technology, its principles and technologies will continue to be optimized and upgraded to adapt to more complex application scenarios.