“The wiring of the CAN bus is affected by the field environment, product shape and other factors, which may lead to the phenomenon of too long/too many bus branches in the field wiring. There are nodes such as CDEF. If the C branch line is extended by 100m, all F will be closed, and the system will report an error. If the 100m extension line is removed, the system will not report an error in any state of F.
The wiring of the CAN bus is affected by the field environment, product shape and other factors, which may lead to the phenomenon of too long/too many bus branches in the field wiring. There are nodes such as CDEF. If the C branch line is extended by 100m, all F will be closed, and the system will report an error. If the 100m extension line is removed, the system will not report an error in any state of F.
When the bus branch line is too long, the rising edge and the falling edge produce step phenomenon. When the step is just near the 0.5V logic recognition threshold, it is easy to cause the bit width to be misaligned, thus causing the receiving node to receive errors. The following solutions are given for such errors:
1. Solution 1 for too many/long bus branches
Use the standard “hand in hand” interface and wiring rules to minimize the branch length. To ensure continuous impedance, the transceiver should be placed close to the interface to reduce the length of the branch stub, and the distance from the transceiver to the interface should be controlled within 10cm.
2. Solution 2 with too many/long bus branches
According to different baud rates, formulate the specification of the longest branch distance.
The branch length specified value for high-speed CAN in ISO11898-1/2 is a maximum of 0.3 meters at 1Mbps. The longest branch for other baud rates is generally defined by the application manufacturer. The principle is:
• Sum of branch lengths + trunk length
• The sum of branches generally does not exceed 30% of the total length.
3. Solution 3 with too many/too long bus branches
The matching of each branch is carried out according to the principle that the longer the branch, the smaller the matching resistance, the matching resistance is between 120-680 ohms, and the total parallel resistance is between 30-60 ohms. For example, in the case of exactly equal length:
R=n×60ohm R:Terminal resistance of each branch n:Number of branches
4. Solution 4 with too many/too long bus branches
Adopt the method of transceiver front and TTL branch to completely solve the branch problem and node expansion problem.
5. Solution 5 for too many/long bus branches
Use CANBridge repeaters, CANHub hubs and other networking equipment for branching. Each of these devices has an independent CAN controller, so each segment can be formed into an independent linear topology, which is convenient for construction.
The above are the solutions summarized by ZLG Ligong Technology and Zhiyuan Electronics based on actual field applications. How to find and locate errors better and faster, and to solve errors, we need to use our CANscope to conduct a comprehensive and systematic analysis of the problem.
CANscope bus analyzer is a comprehensive professional tool for CAN bus development and testing. It integrates mass storage oscilloscope, network analyzer, bit error rate analyzer, protocol analyzer and reliability testing tool. Organic integration and correlation, as shown in the following figure, the software interface diagram of CANscope; redefines the development and testing method of CAN bus, and can conduct multi-angle and all-round evaluation of the correctness, reliability and rationality of CAN network communication; help users to quickly locate Fault node, solve various problems of CAN bus application.