How to achieve data transmission with J1939 to J1708 cable

How to achieve data transmission with J1939 to J1708 cable

The implementation of data transmission through J1939 to J1708 cable is mainly based on protocol conversion and hardware adaptation. Its implementation method and performance characteristics are as follows:

Protocol conversion:

J1939 protocol: Based on CAN bus, supports high-speed data transmission, and supports complex network management and diagnostic functions.

J1708 protocol: Based on RS-485, using a simple message format.

Conversion process: The J1939 to J1708 cable requires converting high-speed and complex messages from J1939 to low-speed and simple messages from J1708.

Hardware adaptation:

J1939 hardware: typically uses shielded twisted pair cables and supports long-distance transmission.

J1708 hardware: also uses twisted pair cables.

Adaptation method: The cable needs to adapt to the requirements of two protocols in the physical layer design, and may use specific circuits and interfaces to achieve signal conversion and transmission.

Conversion Implementation Steps

Hardware interface design

Signal conversion: Convert the differential signal of J1939 into a single ended signal of J1708 using CAN transceiver and RS-485 transceiver.

Level matching: Ensure that the logic levels of the two protocols are compatible.

Isolation protection: Add optocouplers or magnetic couplings between the CAN and RS-485 interfaces to prevent signal interference and voltage surges.

Protocol conversion logic

Data Mapping:

Establish a mapping relationship between the PGN/SPN of J1939 and the MID of J1708. For example, mapping the engine speed of J1939 to a specific MID of J1708.

Process data format conversion (such as byte order, unit conversion).

Adaptation of communication mechanism:

The multi master node communication of J1939 needs to be converted to master-slave communication of J1708. It can be achieved through polling or interrupt mechanism.

Process J1939 broadcast messages and decide whether to broadcast or forward them to specific slave nodes in J1708.

software implementation

Embedded programs: Implement protocol parsing and conversion logic on microcontrollers.

State machine design: Manage protocol states (such as idle, receive, send, error handling).

Error handling: Implement error detection and recovery mechanisms for J1939 and J1708.

test and verification

Functional testing: Verify whether the parsing, mapping, and forwarding of data frames are correct.

Performance testing: Test conversion latency, throughput, and stability.

Compatibility testing: Ensure compatibility with J1939 and J1708 devices from different manufacturers.