The Controller Area Network (CAN) and its successor CAN Flexible Data Rate (CAN FD) are two of the most widely used in-vehicle communication protocols. Both are essential in modern automotive electronics, industrial automation, and embedded systems, where reliable, deterministic, and high-speed data transfer is critical. While Classical CAN has served the automotive industry for decades, the growing demand for faster data transmission, larger payloads, and advanced ECUs led to the development of CAN FD by Bosch in 2012. This article provides a comprehensive explanation of the difference between CAN and CAN FD (CAN vs CAN FD), covering their working principles, architecture, frame formats, data rates, advantages, and application domains.
1. Overview of CAN Protocol
The CAN (Controller Area Network) protocol is a robust serial communication system developed by Bosch in 1986 for the automotive industry. Its purpose was to allow microcontrollers and devices to communicate without a host computer.
CAN vs CAN FD
Key Features of CAN:
- Multi-master serial bus communication.
- Supports broadcast messaging.
- High reliability with error detection mechanisms.
- Deterministic message arbitration using message identifiers.
- Data rate up to 1 Mbps.
- Payload capacity: 8 bytes per frame.
How CAN Works?
CAN uses two differential signal lines — CAN_H and CAN_L — to ensure noise immunity. Messages are transmitted as frames with an identifier (ID) defining message priority. Arbitration ensures that the highest priority message wins access to the bus.
Applications:
- Engine control units (ECUs)
- Body control modules
- Transmission systems
- Anti-lock braking systems (ABS)
- Industrial automation and robotics
2. Limitations of Classical CAN
- Although Classical CAN has proven reliable, it faces challenges in modern automotive systems:
- Limited data payload (8 bytes) restricts the transmission of larger data blocks.
- The maximum speed of 1 Mbps cannot handle high-bandwidth applications like ADAS (Advanced Driver Assistance Systems).
- Overhead increases with the number of ECUs on the network.
- Not optimized for software-over-the-air (SOTA) updates or complex sensor data.
- To overcome these limitations, Bosch introduced an improved version — CAN FD (Flexible Data Rate).
3. Introduction to CAN FD Protocol
What is CAN FD?
CAN FD (Controller Area Network – Flexible Data Rate) is an enhancement of the Classical CAN protocol that supports larger data payloads and higher transmission rates. Introduced in 2012, CAN FD was standardized under ISO 11898-1:2015.
Key Improvements:
- Payload capacity increased from 8 bytes to 64 bytes.
- Data rate increased from 1 Mbps to 8 Mbps.
- Enhanced data integrity and reduced latency.
- Backward compatibility with Classical CAN controllers (for mixed networks).
4. Architecture of CAN vs CAN FD System
Classical CAN Architecture:
- Comprises multiple CAN nodes (controllers, transceivers, ECUs).
- Uses a single shared bus line.
- Employs bitwise arbitration for bus access.
- Transmission and arbitration occur at the same bit rate (≤ 1 Mbps).
CAN FD Architecture:
Similar to CAN but with dual-bit-rate capability:
- The arbitration phase uses classical speed (≤ 1 Mbps).
- The data phase can switch to a higher rate (up to 8 Mbps).
Extended data field for 64-byte payload.
- Supports bit rate switching (BRS) feature.
- Enhanced CRC and data length coding (DLC) for improved integrity.
5. Frame Structure: CAN vs CAN FD
The CAN frame defines how data is transmitted on the network. Let’s compare the frame formats.
Classical CAN Frame Format:
The Classical CAN has four types of frames: Data, Remote, Error, and Overload. The Data Frame consists of:
| Field | Description |
| Start of Frame (SOF) | Marksthebeginningoftransmission |
| Identifier (ID) | Defines message priority |
| Control Field | Includes DLC(DataLengthCode) |
| Data Field | 0 to 8 bytes |
| CRCField | Error detection |
| ACK Field | Acknowledgment slot |
| End of Frame (EOF) | Marksendofmessage |
CAN FD Frame Format:
Key Enhancements in CAN FD Frame:
- BRS Bit: Allows data phase to switch to a higher bit rate.
- ESI Bit: Indicates the transmitter’s error status.
- Extended CRC Field: Provides improved error checking.
- Flexible DLC Coding: Supports up to 64-byte data.
6. Comparison: CAN vs CAN FD7.
| Feature | Classical CAN | CANFD |
| Standard | ISO 11898-1 | ISO 11898-1:2015 |
| DataRate | Up to 1Mbps | Up to 8Mbps |
| Payload Size | 0–8 bytes | 0–64 bytes |
| Bit Rate Switching | Notsupported | Supported(BRS bit) |
| CRC Length | 15-bits | 17 or 21 bits |
| Error Handling | Basic error detection | Enhanced error detection |
| Error Handling | Basic error detection | Enhanced error detection |
| Protocol Efficiency | Moderate | Higher (less overhead) |
| Backward Compatibility | – | Backward compatible with Classical CAN controllers |
| Use Cases | Engine, body control, ABS | ADAS, infotainment, sensor fusion |
| Latency | Higher | Lower |
| Bandwidth Utilization | Limited | Improved |
| Transmission Speed in the Data Phase | Fixed | Variable (upto8Mbps) |
7. Working Difference Between CAN and CAN FD
CAN Operation:
In Classical CAN, every frame — including arbitration, control, and data — is transmitted at the same bit rate. This makes it reliable but limits the throughput.
CAN FD Operation:
In CAN FD, the arbitration phase (where ECUs compete for bus access) occurs at the classical rate (1 Mbps). Once arbitration completes, the data phase can switch to a higher rate (2–8 Mbps) using the BRS bit. Thus, CAN FD achieves faster data transmission without compromising compatibility.
8. Data Length and CRC Enhancement
CRC Enhancement:
| DLC | Data Length Bytes) |
| 0–8 | 0–8 |
| 9–15 | 12,16,20,24,32,48,64 |
This ensures higher reliability for larger payloads.
9. Bit Timing and Synchronization
In CAN FD, bit timing parameters such as Propagation Segment, Phase Segment 1, and Phase Segment 2 are optimized separately for arbitration and data phases. This allows faster bit timing in data transmission while maintaining robust synchronization in arbitration.
10. CAN FD in Mixed Networks
One of the major advantages of CAN FD is backward compatibility. In a mixed network, CAN FD controllers can coexist with Classical CAN controllers. However, Classical CAN nodes cannot interpret FD frames, so the FD node must operate in CAN-compatible mode when transmitting to classical nodes. This enables a gradual migration from legacy CAN to CAN FD networks in vehicles.
11. Advantages of CAN FD Over Classical CAN
| Feature | Advantage in CAN FD |
| Higher Bandwidth | Upto 8Mbps for faster transmission |
| Increased Payload | 64 bytes per frame reduces the frame |
| Improved Efficiency | Fewer messages needed for large data |
| Lower Latency |
Faster data phase reduces response time
|
| Enhanced Reliability | Stronger CRC and error detection |
| Backward Compatibility | Coexistence with Classical CAN nodes |
| Software-Friendly |
Supports firmware updates and diagnostics
|
| Reduced Bus Load | Optimized bandwidth utilization |
Example:
In a scenario where an ECU needs to send 64 bytes of data:
- Classical CAN requires 8 frames (8 bytes each).
- CAN FD needs only one frame, transmitted up to 8× faster.
Hence, CAN FD improves performance almost 64 times in data-heavy applications.
12. Applications of CAN FD
Automotive Systems:
- Advanced Driver Assistance Systems (ADAS)
- Battery Management Systems (BMS)
- Infotainment and Telematics
- Electric & hybrid vehicle control
- Powertrain and chassis domain controllers
Industrial & Other Domains:
- Robotics and factory automation
- Avionics systems
- Marine control systems
- IoT-enabled embedded devices
13. Limitations of CAN FD
Despite its advantages, CAN FD has certain challenges:
- Hardware upgrade required: Classical CAN controllers cannot interpret FD frames.
- Higher EMC sensitivity: Faster bit rates increase electromagnetic interference risk.
- Software complexity: More configuration is needed for dual-bit-rate management.
- Cost: Slightly higher due to new transceivers and controllers.
14. Migration from CAN to CAN FD
Steps for Migration:
- Evaluate network performance – Identify bottlenecks in classical CAN.
- Upgrade ECUs – Replace controllers with CAN FD-compatible ones.
- Update transceivers – Ensure physical layer compliance (ISO 11898-2:2016).
- Modify software drivers – Incorporate new DLC and BRS handling.
- Validate network timing – Adjust bit timing parameters for arbitration and data phases.
- Backward compatibility testing – Verify mixed network performance.
By adopting these steps, automotive OEMs can gradually transition from Classical CAN to CAN FD without overhauling the entire network.
15. CAN FD vs Other Automotive Protocols
Thus, CAN FD fills the mid-tier gap between CAN and automotive Ethernet — providing both speed and reliability at a lower cost.
|
Protocol |
DataRate | Payload |
Application |
|
CAN (Classical) |
1Mbps | 8bytes | Powertrain, body electronics |
|
CAN FD |
8Mbps | 64bytes |
ADAS, diagnostics, infotainment |
| LIN |
20Kbps |
8bytes | Low-cost sensors/actuators |
|
FlexRay |
10Mbps | 254 bytes y |
Safety-criticalsystems |
|
Ethernet(Automotive) |
100Mbps–1 Gbps | 1500 bytes |
High-speed ADAS, cameras |
16. Future Trends: CAN XL
As automotive systems become more data-driven, Bosch and the CAN community are developing CAN XL, the next generation of CAN.
CAN XL Key Highlights:
- Data payload up to 2048 bytes.
- Data rate up to 20 Mbps.
- Compatible with CAN and CAN FD.
- Targeted for zonal architectures in vehicles.
CAN FD will remain the mainstream protocol for many years, while CAN XL will extend its functionality for high-performance domains.
17. Summary Table: CAN vs CANFD
|
Parameter |
ClassicalCAN |
CANFD |
|
Year Introduced |
1986 |
2012 |
|
Developer |
Bosch |
Bosch |
|
Standard |
ISO11898-1 |
ISO11898-1:2015 |
|
MaxData Rate |
1Mbps |
8Mbps |
|
Payload |
8bytes | 64bytes |
| BitRate Switching | No |
Yes |
|
CRC |
15-bits | 17 or 21 bits |
|
DataPhaseSpeed |
Fixed |
Flexible |
| BackwardCompatibility | N/A |
Supported |
18. Conclusion
Both CAN and CAN FD are integral communication protocols in automotive and industrial embedded systems. While Classical CAN remains reliable for low-speed control networks, CAN FD delivers the speed, payload capacity, and efficiency required by modern vehicles with complex ECUs and high data demands.
In essence:
- CAN = Reliability and simplicity
- CAN FD = Performance and scalability
The transition to CAN FD is inevitable as vehicles evolve into software-defined, connected, and autonomous systems. With higher bandwidth, lower latency, and backward compatibility, CAN FD is now the industry standard for next-generation automotive communication networks.
1. What is the main difference between CAN and CAN FD?
The primary difference is that Classical CAN supports up to 1 Mbps speed and 8 bytes of payload, whereas CAN FD supports up to 8 Mbps speed and up to 64 bytes of payload. CAN FD also uses a Bit Rate Switch (BRS) to increase speed during the data phase and provides enhanced CRC for better reliability.
2. Is CAN FD backward compatible with Classical CAN?
Yes. CAN FD controllers are backward compatible, meaning they can communicate with Classical CAN nodes using Classical CAN frames. However, Classical CAN nodes cannot decode CAN FD frames, so mixed networks require careful configuration where FD-capable nodes send only classical frames when needed.
3. Why is CAN FD faster than Classical CAN?
CAN FD is faster because it:
- Uses bit rate switching (BRS) to increase data phase speed up to 8 Mbps.
- Allows larger payloads (64 bytes), reducing the number of frames needed.
- Has reduced overhead, improving overall bus efficiency.
These features combined significantly increase throughput compared to Classical CAN.
4. Can CAN FD replace CAN in all automotive applications?
In most modern vehicles, CAN FD is gradually replacing Classical CAN, especially for ADAS, infotainment, and battery management systems. However, Classical CAN is still sufficient for:
- Basic body control modules
- Low-bandwidth sensors
- Simpler ECUs
Thus, CAN and CAN FD will co-exist in vehicles for several years.
5. What applications require CAN FD instead of Classical CAN?
CAN FD is preferred for applications that need higher bandwidth and faster response, such as:
- ADAS and autonomous control systems
- Battery Management Systems (BMS)
- High-speed sensor fusion
- Infotainment and telematics
- Over-the-air (OTA) ECU updates
- These systems often need larger data blocks and real-time processing, which Classical CAN cannot efficiently.
6. What is the maximum data rate and payload size in CAN FD?
CAN FD supports:
- Data rate: Up to 8 Mbps in the data phase
- Payload: Up to 64 bytes per frame
Compared to Classical CAN’s 1 Mbps and 8 bytes, CAN FD provides significantly higher performance for modern automotive networks.