One advantage of J1939 cable: multi frame transmission

One  advantage of J1939 cable: multi frame transmission

One of the core advantages of J1939 cable is its support for multi frame transmission of long data, which achieves data partitioning and reassembly through transmission protocol (TP), breaking through the limitation of 8 bytes of effective data in CAN frames. This mechanism is jointly implemented by two PGNs, TP.CM (Connection Management) and TP.DT (Data Transmission), to ensure efficient and accurate transmission of large amounts of data, such as fault diagnosis logs and engine parameter curves.

During the transmission process, the sender first sends a "Request to Send" (RTS) message through TP.CM, which contains key information such as the total number of bytes, the number of data packets, and the maximum allowed number of consecutive packets to be sent. After the receiver replies with "Allow to Send" (CTS), the sender begins to transmit data packet by packet, with the first byte of each packet being the sequence number (1-255) and the following 7 bytes being valid data. The recipient reassembles the data based on the sequence number and confirms the transmission completion through an End of Message (EOM). If there is a packet loss or error during transmission, the receiver can send an "ABORT" request to the sender to resend the specified packet.

The TP protocol also supports a "flow control" mechanism, which dynamically adjusts the sending rate through CTS messages to avoid data overflow caused by insufficient processing capacity of the receiver.

From the data link layer to the application layer, the multi frame transmission mechanism of J1939 cable provides efficient and stable big data communication capabilities for commercial vehicles, becoming a key technical support for vehicle intelligence and diagnostic function expansion.