The basics of the controller area network (CAN bus) and its use in automotive applications
In CAN FD, the clock rate during the data and CRC fields is increased so that twice as much data can be transmitted in the same period of time, or the same amount of data can be transmitted in half the time, giving CAN FD a greater bandwidth. The rest of the protocol timing remains the same. This arrangement is backward compatible, and CAN FD devices can operate in a CAN environment. Additionally, CAN FD supports data fields as large as 64 bytes compared to the eight-byte limit of CAN, which also increases the data rate.
If the bit sequence contains five or more bits of the same state, then the controller will insert a stuff bit of the opposite state to ensure that there are sufficient edges in the signal to maintain synchronization. These stuff bits are removed by the receiver so that the data content is correct. After the CRC field, bit stuffing is deactivated to ensure that the ACK and EOF fields do not show stuff bits.
CAN XL increases the data rate and data payload size. The data payload length is increased to a maximum of 2048 bytes, accounting for the name “extra long.” CAN XL still maintains backward compatibility with CAN and CAN FD for operation at lower speeds.
What’s ahead for CAN bus? The high end of the in-vehicle network spectrum is occupied by 100BASE-T and 1000BASE-T Ethernet networks. There is quite a gap between lower- speed buses like CAN FD at 5 Mbps and these higher-speed buses. Currently, there are two contenders under development in the 10 Mbps space, namely 10BASE-T1S and CAN XL.
Differences between CAN and CAN FD We already know that CAN FD operates at data rates of up to 5 Mbps compared to the 1 Mbps maximum data rate for CAN. This improvement is accomplished by increasing the data clock rate selectively; hence the name CAN FD (Figure 7).
Conclusion The CAN bus two-wire twisted pair interface has been around for many years and continues to grow to meet the expanding array of automobile connectivity requirements. It can be used by itself or to complement single-wire networks like LIN to minimize overall weight and cost. It is supported by a variety of classic and CAN FD transceivers from companies such as Texas Instruments.
Figure 7: CAN FD uses a variable data rate in the data and CRC frames to increase the overall data rate of the transfer. (Image source: Texas Instruments)
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