What is CAN FD?

With the rapid development of automotive electronics and industrial automation, the number of devices and the amount of data on the CAN bus have greatly increased, which brings great challenges to the CAN bus. In order to meet higher bandwidth and data throughput, CAN FD (CAN with Flexible Data-Rate) was born.

The origin of CAN FD

Since its inception in the 1880s, the CAN bus has been widely used in the automotive and industrial control industries. However, with the rapid development of automotive electronics and industrial automation, the number of devices and data on the bus are greatly increased, while the traditional CAN can only support the transmission rate of up to 1 Mbit/s, which brings great challenges to CAN communication. . To meet higher bandwidth and data throughput, CAN FD came into being.

CAN FD features

1, higher transmission rate

The data segment of the CAN FD can be transmitted at a higher rate, such as 5 Mbit/s. In order to ensure the robustness and reliability of the bus, the arbitration segment (ID and ACK) remains unchanged, using standard rate transmission (up to 1 Mbit/s). The measured waveform comparison is shown in Figure 1 and Figure 2.

Figure 1 Traditional CAN bus waveform

Figure 2 CAN FD bus waveform

2, more data bytes

A traditional CAN frame can only transmit up to 8 bytes of data, while a CAN FD can transmit up to 64 bytes in a frame, which can effectively avoid data split transmission. The measured waveform comparison is shown in Figure 3 and Figure 4.

Figure 3 Traditional CAN data segment

Figure 4 CAN FD data segment

How to upgrade CAN to CAN FD

1. Need to use MCU or controller supporting CAN FD protocol

As an upgrade of CAN2.0, CAN FD can be backward compatible with CAN2.0 standard, that is, CAN FD node can receive data of traditional CAN node, but traditional CAN node can not receive CAN FD message correctly. 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. Transceivers that need to support higher transmission rates

The increase in transmission rate also places higher demands on the CAN transceiver. If the maximum rate of the designed CAN FD node is 5 Mbit/s, the transmission rate of the transceiver must also reach this value.

CAN FD isolation

CAN FD and traditional CAN are not much different in practical applications, cable selection, topology selection, bus layout, etc. are similar. In some cases where interference is severe, isolation is still essential. Isolation can avoid potential high voltage hazards, eliminate ground potential differences and ground loops, thus greatly improving the reliability of communication.

ZLG Zhiyuan Electronics' latest CAN FD isolated CAN transceivers CTM5MFD and CTM3MFD are compact and can support transmission rates up to 5Mbit/s. It is an ideal solution for CAN FD isolation applications.