SAE J1939 with CAN FD represents a significant advancement in vehicle networking, particularly for heavy-duty trucks, agricultural equipment, and industrial machinery. Traditionally, the SAE J1939 protocol operated on the classical CAN bus at data rates of 250 kbit/sec or 500 kbit/sec, which could become a bottleneck as modern vehicles require faster and more efficient communication. By integrating CAN FD (Controller Area Network with Flexible Data-Rate), J1939 can now support much higher data throughput—up to 8 Mbit/sec—while also increasing the maximum payload size from 8 bytes to 64 bytes. This enhancement reduces network congestion, minimizes latency, and allows for faster data exchanges between Electronic Control Units (ECUs), improving vehicle performance and responsiveness.
The implementation of CAN FD in J1939, as outlined in the SAE J1939-22 standard, ensures backward compatibility while leveraging the benefits of flexible data rates. By maintaining the arbitration phase at traditional speeds and switching to higher rates during data transmission, CAN FD optimizes real-time control applications such as engine management, advanced diagnostics, and predictive maintenance. This upgrade is particularly beneficial for applications requiring large data transfers, such as telematics, over-the-air updates, and ADAS (Advanced Driver Assistance Systems). As commercial vehicles continue to adopt smarter technologies, SAE J1939 with CAN FD provides the robust, scalable network architecture needed to meet the increasing demands of modern transportation and automation.
1. Network Architecture Upgrades
- Hardware Compatibility:
- CAN FD requires newer CAN controllers that support variable bit rate operation.
- Legacy ECUs using standard CAN (250/500 kbit/sec) must be upgraded or connected through a gateway ECU.
- Physical Layer Considerations:
- CAN FD maintains the same differential signaling (CAN_H, CAN_L) as classical CAN.
- Higher bit rates require better signal integrity, shorter bus lengths, and possibly improved shielding.
2. Backward Compatibility Management
-
Dual CAN Networks:
- One classic CAN network (250 or 500 kbit/sec) for legacy J1939 ECUs.
- A CAN FD network for high-speed communication between modern ECUs.
- A gateway ECU can bridge messages between the two networks.
-
Mixed CAN and CAN FD Operation:
- Classical CAN nodes ignore CAN FD frames (due to format differences).
- J1939-22 (the updated CAN FD-based J1939 standard) specifies handling mechanisms for mixed networks.
3. Adapting J1939 Messaging for CAN FD
-
J1939-22 Specification:
- The SAE J1939-22 standard defines how CAN FD operates within the J1939 protocol.
- Multi-packet messages (TP.CM, TP.DT) used in classical J1939 are no longer needed due to larger 64-byte frames.
-
Parameter Group Number (PGN) Adjustments:
- J1939 messages must be adapted to use CAN FD frame formats.
- New PGNs are defined to support faster data transmission and larger payloads.
4. Use Cases for CAN FD in J1939
-
Powertrain and Engine Control:
- Faster exchange of sensor data (e.g., fuel injection, turbo pressure, exhaust gas temperature).
- Reduced delay in critical control loops.
-
Advanced Driver Assistance Systems (ADAS):
- Faster communication for radar, LiDAR, and camera-based collision avoidance.
- Enhanced real-time processing for lane-keeping, adaptive cruise control.
-
Telematics and Predictive Maintenance:
- More efficient diagnostics logging and OTA updates.
- Higher data throughput for fleet monitoring and remote troubleshooting.
Conclusion
The integration of CAN FD into SAE J1939 is a necessary evolution to support the increasing data needs of modern commercial vehicles and machinery. By increasing the data rate up to 8 Mbit/sec and expanding the payload size to 64 bytes, CAN FD dramatically improves efficiency, latency, and overall network performance. Implementing J1939-22 ensures backward compatibility while leveraging the full potential of CAN FD, making it a future-proof solution for vehicle communication networks.
SAE J1939 Starter Kit and Network Simulator
Our JCOM.J1939 Starter Kit and Network Simulator is designed to allow the experienced engineer and the beginner to experiment with SAE J1939 data communication without the need to connect to a real-world J1939 network, i.e., a diesel engine. It may sound obvious, but you need at least two nodes to establish a network. That fact applies especially to CAN/J1939, where the CAN controller shuts down after transmitting data without receiving a response. Therefore, our JCOM.J1939 Starter Kit and Network Simulator consists of two J1939 nodes, namely our JCOM.J1939.USB, an SAE J1939 ECU Simulator Board with USB Port.
The JCOM.J1939.USB gateway board is a high-performance, low-latency vehicle network adapter for SAE J1939 applications. The board supports the full SAE J1939 protocol according to J1939/81 Network Management (Address Claiming) and J1939/21 Transport Protocol (TP).
Comments are closed.