With the rapid development of automotive electronics and industrial automation, both the number of devices on the CAN bus and the volume of data have increased significantly, posing major challenges for the CAN bus. To meet the demand for higher bandwidth and data throughput, CAN FD (CAN with Flexible Data-Rate) was developed.
The Origins of CAN FD
Since its inception in the 1980s, the CAN bus has been widely used in industries such as automotive and industrial control. However, with the rapid development of automotive electronics and industrial automation, both the number of devices on the bus and the volume of data have increased significantly. Since traditional CAN can only support a maximum transmission rate of 1 Mbit/s, this has posed significant challenges for CAN communication. To meet the demand for higher bandwidth and data throughput, CAN FD was developed.
Features of CAN FD
1. Higher Transmission Rates
Data segments in CAN FD can be transmitted at higher rates, such as 5 Mbit/s. To ensure the robustness and reliability of the bus, arbitration segments (ID and ACK) remain unchanged and are transmitted at the standard rate (up to 1 Mbit/s). A comparison of measured waveforms is shown in Figures 1 and 2.
Figure 1: Traditional CAN Bus Waveform
Figure 2: CAN FD Bus Waveforms
2. More Data Bytes
A traditional CAN frame can transmit a maximum of 8 bytes of data, whereas a CAN FD frame can transmit up to 64 bytes, effectively eliminating the need to split data into multiple frames. A comparison of actual waveforms is shown in Figures 3 and 4.
Figure 3: Traditional CAN Data Segment
Figure 4: CAN FD Data Segment
How to Upgrade from CAN to CAN FD
1. You need to use an MCU or controller that supports the CAN FD protocol.
As an upgrade to CAN 2.0, CAN FD is backward compatible with the CAN 2.0 standard. This means that CAN FD nodes can receive data from traditional CAN nodes, but traditional CAN nodes cannot correctly receive CAN FD messages. Therefore, on a bus that contains both CAN FD nodes and traditional CAN nodes, only CAN messages in the traditional format can be used.
2. A transceiver supporting higher data rates is required
The increase in data rate places higher demands on CAN transceivers. If the maximum data rate of the designed CAN FD node is 5 Mbit/s, the transceiver's data rate must also reach this value.
CAN FD Isolation
In practical applications, there is little difference between CAN FD and traditional CAN; cable selection, topology choice, and bus layout are largely similar. However, in environments with severe interference, isolation remains essential. Isolation can prevent potential high-voltage hazards, eliminate ground potential differences and ground loops, thereby significantly improving communication reliability.
ZLG Zhiyuan Electronics' newly launched CAN FD isolated CAN transceivers, the CTM5MFD and CTM3MFD, feature a compact design and support data rates of up to 5 Mbit/s, making them ideal solutions for CAN FD isolation applications.