# How to choose several topologies of the mainstream CAN bus?

As the application of CAN bus becomes more and more extensive, how to choose a suitable network topology has become a headache for engineers in the face of various working conditions. This article will introduce several mainstream bus topologies, which can help you quickly understand how to choose.

As the application of CAN bus becomes more and more extensive, how to choose a suitable network topology has become a headache for engineers in the face of various working conditions. This article will introduce several mainstream bus topologies, which can help you quickly understand how to choose.

1. Linear topology Figure 1 Linear topology

Linear topology is also called bus topology. As shown in Figure 1, all nodes are connected to the same bus. Any node on the bus sends information, and other nodes can receive it normally.

-Simple wiring construction;

-Impedance matching fixed rules (one 120 ohm resistance matching at the beginning and the end);

-Wiring operation is simple and convenient.

Because of these advantages, it has been widely used in many fields and can meet the application requirements of most fields. However, with the expansion of industry applications, the shortcomings of bus topology are gradually discovered, such as:

-If the number of nodes is large, the bus cable becomes longer, which will affect the bus transmission;

-The length of the branch line cannot be too long.

Two, star topology

We can see that the characteristic of the star topology is that each branch is basically equal in length. In the case of complete equal length, you can achieve networking without using a hub device and adjusting the terminal resistance (R=n×60 ohm; R: each The terminal resistance of the branch; n: the number of branches). If the length of each branch line is different, it is necessary to use a hub to control the communication to ensure the stable transmission of data.

The advantages of this topology are:

-It is more convenient for node expansion;

-Can reduce the use area of ​​bus application scenarios.

However, the disadvantages of this topology are also obvious, such as:

-Failure of the central equipment will cause the network to be paralyzed;

-Impedance matching is complicated when the branches are unequal length;

-Also need to increase the hub for network topology segmentation.

Three, tree topology Figure 3 Tree topology

The tree topology is characterized by longer branches and different lengths. As shown in Figure 3, it can be seen that because the length of each branch is different, impedance matching is difficult, and hubs and repeaters are often used for branching. Each of these devices has an independent CAN controller, so each section can be formed into an independent linear topology, which is convenient for construction.

The advantages of this topology are:

-Convenient wiring construction;

-Minimize the wiring distance.

However, the disadvantages of this topology are also obvious, such as:

-The network topology is complex, and construction personnel cannot perform impedance matching;

-A hub or repeater must be added to split the network topology. Figure 4 Tree topology application

As shown in Figure 4, it is a tree topology application model. Because the overall transmission distance is too long, a repeater must be added every five kilometers to ensure the signal transmission quality. Each subnet node is connected through CANbridge. , The data of each node in the subnet is sent and received and filtered through CANbridge, thus completing the overall network networking. Figure 5 Ring topology

Four, ring topology

The ring topology connects the CAN bus end to end to form a ring to ensure that the cable is disconnected at any position and communication can still be ensured. As shown in Figure 5, it can be seen that due to the ring structure, the distributed matching method is used in the terminal resistance matching to ensure that the overall impedance is 60 ohms.

Formula: R=120Ω, Rct1=Rct10=300Ω, Rct2~Rct9=5k

-Advantage: After the cable is disconnected at any position, the bus can still communicate.

-Disadvantages: After disconnection, the signal reflection is serious, and it cannot be used in high baud rate and long-distance occasions.

Summarize Figure 6 Summary of topology

As shown in Figure 6 is a summary of these four mainstream topological methods. When choosing a network layout, you can make a choice based on the advantages and disadvantages of different topological methods to quickly complete the selection.

As the application of CAN bus becomes more and more extensive, how to choose a suitable network topology has become a headache for engineers in the face of various working conditions. This article will introduce several mainstream bus topologies, which can help you quickly understand how to choose.

As the application of CAN bus becomes more and more extensive, how to choose a suitable network topology has become a headache for engineers in the face of various working conditions. This article will introduce several mainstream bus topologies, which can help you quickly understand how to choose.

1. Linear topology Figure 1 Linear topology

Linear topology is also called bus topology. As shown in Figure 1, all nodes are connected to the same bus. Any node on the bus sends information, and other nodes can receive it normally.

-Simple wiring construction;

-Impedance matching fixed rules (one 120 ohm resistance matching at the beginning and the end);

-Wiring operation is simple and convenient.

Because of these advantages, it has been widely used in many fields and can meet the application requirements of most fields. However, with the expansion of industry applications, the shortcomings of bus topology are gradually discovered, such as:

-If the number of nodes is large, the bus cable becomes longer, which will affect the bus transmission;

-The length of the branch line cannot be too long.

Two, star topology

We can see that the characteristic of the star topology is that each branch is basically equal in length. In the case of complete equal length, you can achieve networking without using a hub device and adjusting the terminal resistance (R=n×60 ohm; R: each The terminal resistance of the branch; n: the number of branches). If the length of each branch line is different, it is necessary to use a hub to control the communication to ensure the stable transmission of data.

The advantages of this topology are:

-It is more convenient for node expansion;

-Can reduce the use area of ​​bus application scenarios.

However, the disadvantages of this topology are also obvious, such as:

-Failure of the central equipment will cause the network to be paralyzed;

-Impedance matching is complicated when the branches are unequal length;

-Also need to increase the hub for network topology segmentation.

Three, tree topology Figure 3 Tree topology

The tree topology is characterized by longer branches and different lengths. As shown in Figure 3, it can be seen that because the length of each branch is different, impedance matching is difficult, and hubs and repeaters are often used for branching. Each of these devices has an independent CAN controller, so each section can be formed into an independent linear topology, which is convenient for construction.

The advantages of this topology are:

-Convenient wiring construction;

-Minimize the wiring distance.

However, the disadvantages of this topology are also obvious, such as:

-The network topology is complex, and construction personnel cannot perform impedance matching;

-A hub or repeater must be added to split the network topology. Figure 4 Tree topology application

As shown in Figure 4, it is a tree topology application model. Because the overall transmission distance is too long, a repeater must be added every five kilometers to ensure the signal transmission quality. Each subnet node is connected through CANbridge. , The data of each node in the subnet is sent and received and filtered through CANbridge, thus completing the overall network networking. Figure 5 Ring topology

Four, ring topology

The ring topology connects the CAN bus end to end to form a ring to ensure that the cable is disconnected at any position and communication can still be ensured. As shown in Figure 5, it can be seen that due to the ring structure, the distributed matching method is used in the terminal resistance matching to ensure that the overall impedance is 60 ohms.

Formula: R=120Ω, Rct1=Rct10=300Ω, Rct2~Rct9=5k

-Advantage: After the cable is disconnected at any position, the bus can still communicate.

-Disadvantages: After disconnection, the signal reflection is serious, and it cannot be used in high baud rate and long-distance occasions.

Summarize Figure 6 Summary of topology

As shown in Figure 6 is a summary of these four mainstream topological methods. When choosing a network layout, you can make a choice based on the advantages and disadvantages of different topological methods to quickly complete the selection. 