Analysis of Lin network solution for the hottest c

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Analysis of automobile Lin network solution

in terms of centralized control of all automobile nodes, local interconnect network (Lin) provides a low-speed, low-cost implementation method. LIN bus is an automobile serial protocol developed for low-cost applications. It complements the existing can network and supports the layered network in the vehicle. This paper discusses several Lin networking solutions, and compares the advantages and disadvantages of each solution

lin bus is an automobile serial protocol developed for low-cost applications. It is a supplement to the existing can network and supports the layered network in the vehicle. The protocol is a simple master/slave configuration, and the main process is completed on the master node. In order to reduce the cost, the slave node should be as simple as possible

lin bus is a master-slave protocol, and all data transmission in the bus is initiated by the master node. Now there are two completely different ways to transmit data to the slave node, that is, master-slave transmission (the slave task in the master node transmits data) or slave-slave transmission (the master node sends the frame header, transmits data from a slave node, and then receives the data from another slave node). These two methods have different advantages and disadvantages

lin protocol is time triggered and does not need bus arbitration. It can also calculate the timing of each information frame in the worst environment. The transmission of each information frame is controlled by the scheduling table executed on the master node. The scheduling table transmits information frame headers at a given time

network implementation

this section mainly introduces all aspects of a single Lin network, multiple Lin networks and hybrid can/lin networks

1. Single Lin network (multiple door nodes)

in this kind of network, the body controller module (BCM) will be connected to all other nodes through a single Lin network. As shown in Figure 1:

Lin connection diagram

this kind of network has a very direct structural system, and Lin connection effectively replaces the can solution. Although the Lin protocol was originally designed to supplement (rather than replace) can, the connection shown in Figure 1 can realize a simple Lin solution

this is also a solution that can reduce costs, because it does not require any can nodes. BCM is the master node of Lin network, and all Lin nodes can access all information transmitted on LIN network. With this solution, there are usually five Lin nodes on the network. Reducing the number of nodes and defining the initial information transmission method make the network more direct and effective

however, it is difficult to make a schedule (define which information will appear in what order in the network). If the system uses slave node - slave node communication, it can simplify the formulation process of the schedule, because it minimizes the network traffic. For example, if a door has any keyboard operation, the master node needs to make a decision: any node on the network can respond within the same information frame

this kind of network information flow is the shortest, which causes the least EMC problems. At the same time, the reduction of flow density also helps to reduce radiation. In addition, since all nodes are connected by one line, the number of joints is minimized, which increases reliability

2. Two Lin networks

in order to overcome the shortcomings of a single Lin network, some companies began to use dual Lin networks. As shown in Figure 2

figure 2:2 schematic diagram of Lin network connection

bcm controls two completely independent Lin networks, which makes it relatively simple to formulate the schedule, and the network flexibility is also enhanced. Even if there is a crash, most of the networks are very likely to remain intact, and they can still remain intact. At the same time, two completely independent Lin networks are used, which is conducive to timely communication

3. Can with Lin layered structure

relying on Lin alone cannot overcome all the limitations. So, how to apply Lin in automotive applications? We mentioned in the previous introduction that Lin is a supplement to can, not a complete replacement of can. Figure 3 is the solution of can/lin hybrid network:

Figure 3: canlin hybrid network solution

as mentioned above, BCM and four doors are usually connected through a can network. This is a typical scheme adopted by a large number of manufacturers at present. At this time, the high-performance controller (MCU) in each door, such as the common Freescale hc908az60a, directly controls the windows and mirrors

using Lin structure to realize door function, you can choose MCU with smaller specification (such as hc908gz16). In addition to providing necessary can interface for BCM communication, it also has enough resources to control a single Lin network. In this example, the driver's door MCU is not only the can interface of BCM, but also the main node of Lin network that controls the operations of rearview mirror, keyboard, lock and window lifting

although this will increase the MCU in the door, if the MCU and Lin state machine are properly selected, a more powerful and flexible distributed system can be obtained

4. Door control

the previous example introduces the typical Lin network inside the door, and also puts forward solutions to the limitations mentioned above. However, there are still several problems in the door network, especially the function failure and the rise in the spot market price of imported ore; The market price of domestic ore is stable; The billet market was mixed; Coke spot market remains strong; The maritime market continues to fall, with safety issues. The car mirror is the most easily damaged component in the system. It is often taken away when driving in urban areas, resulting in network interruption and even unbearable risks to some manufacturers. In terms of security, a large number of criminals can easily remove the car mirror, so as to obtain direct access to the driver's door MCU. This is another major risk

there are several ways to reduce this risk. One method is shown in Figure 4:

Figure 4: Lin network door solution 1

in this example, there are two Lin networks inside the door. As can be seen from Figure 4, the mirror is effectively separated from other parts of the system, greatly reducing the harm caused by the removal of the mirror. Any criminal behavior can only access the driver's door MCU, but cannot access key components, such as door locks

Figure 5: Lin door solution 2

there is another way to control the mirrors through Lin sub nodes. In this case, both safety and reliability issues can be effectively resolved. The car mirror is directly controlled by the keyboard MCU or Lin node. Both methods are suitable for system design

typical Lin node

the Lin network inside the door is introduced above. The following is an example of a common Lin node in the vehicle

1. Driver door module

in the above system, this module is the main node of the door network and provides the control and timing functions of the internal Lin network of the door. It can control all Lin nodes in the door and also act as a switch between the body control module (BCM) and the local Lin network

2. Rearview mirror module

typical new rearview mirrors can usually support x, Y directions and folding functions. The mirror module also stores detailed information such as the position of the mirror. Sometimes, the driver or passenger mirror is also equipped with a temperature sensor to continuously monitor the external environment. This information is generally used as driver information, but also as complex engine management system information. The mirror module is usually a Lin slave node

3. Window lifting module

electronic window includes lifting, lowering and anti pinch control. The window lifting node is generally a Lin slave node. Sometimes, the front window module acts as the Lin slave node of the BCM and the master node of the rear door at the same time

4. The lock function of the door lock module includes "standard lock" and "child lock". The Lin inside the door is directly connected to the module, which is also the prerequisite for realizing the child lock function, so that the driver can cancel the specific door lock function. The door lock module is generally a Lin slave node

5. Front switch panel

a large number of functions of vehicle comfort control (such as door locking, window lifting and mirror control switches) are sometimes integrated into a single module as a slave node of Lin network

communication method

as mentioned above, the data communication of Lin network mainly includes two different methods: Master slowly open the oil delivery valve, slave data transmission or slave slave data transmission. Both methods are controlled by the master node and have their own advantages and disadvantages

1. Master slave communication "

the master node transmits the information ID, and then sends the data transmission command. All Lin nodes on the convert this information, and then perform corresponding operations

according to the master-slave communication mode, there is a slave node running inside the master node. It responds to the correct ID and then transmits the specified bits to the LIN bus. Different Lin nodes have complete Lin frames in the network, and also provide master node data and processes according to their different applications

for example, the master node may want all door locks to be opened, so that each door lock node is set to respond to a single message, and then complete unlocking; Or the master node may transmit four different messages and selectively unlock the door

the master-slave communication mode transfers most scheduling operations to the master node, thereby simplifying the operations of other nodes. Therefore, Lin slave node hardware is greatly reduced, and may even be reduced to a single state device. Another advantage is that because the master node can communicate with all nodes at the same time, the number of information and required IDs are greatly reduced

the master node sends all data communications to all nodes (and then receives the data from the nodes before all data is transmitted to other devices), so that the validity of the transmitted data can be checked. This operation allows the master node to monitor all communications to reduce or eliminate potential errors

however, this communication method is slow. At this time, it is difficult for Lin nodes to receive and process data in time and selectively transmit it to other nodes

2. The Slave Slave Communication

master node also sends the information frame header. However, in the slave slave communication mode, the remote node, such as the keyboard, responds to the "slave task". When the keyboard is "filled" with information frame data bytes, all nodes on the can see the whole transmission process and respond to the corresponding operations. In this example, the window Lin slave node responds to the keyboard Lin node data

compared with master-slave communication, the slave-slave communication method is faster. The nodes on each information frame share information, which greatly improves the response speed. A single message can open two windows, close one door, open three doors, or move the window. This can significantly reduce the data traffic on

however, the slave slave communication method also has shortcomings: first, the clock source of each slave node is unknown, so when the slave node transmits data to the network (according to the request of the master node), the data may drift. The master node has a clock with high accuracy, so there is a high-level tolerance range for data drift, which will reach 2trillion yuan by 2015, but the other Lin slave node receiving data is not so high, which will lead to data mistranslation. Secondly, in this case, the master node does not display that the "Slave Slave" communication has failed

information frame transmission duration

the following table describes the maximum duration of 2, 4, and 8-byte information when the transmission rate is 600bit/sec and 19200bit/sec. This protocol is dedicated to the operation between 1kbps and 20kbps, and it is recommended to use these transmission rates in Lin technical specifications. As shown in Table 1. Table 1: the transmission duration of information frames in Lin specification

these data may appear to be very slow (especially when compared with can), but there are many reasons for this regulation. The two main reasons are to minimize EMC radiation and simplify slave nodes

summary of this article

with some intelligent control functions of cars

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