The CAN bus and CAN bus-based diagnostics are not a concept at all, and the hardware of the CAN bus is not necessarily the hardware of the OBD. As for "going to the 4S shop to ask the technicians, most of the people in the car factory are not necessarily more knowledgeable than these people." Do you let these technicians write me a ECU CAN interface that can be used?
The following is the official answer.
First of all, please see the paper "CAN Bus System Test Technology" written by Hengrun engineers.
The basic description of the CAN bus development process, but mainly focused on the CAN bus test, but also allows you to understand.
Based on your description, assume that your requirements are: based on an embedded platform (preferably the platform is widely used in automotive ECU development), writing CAN interface code according to a given communication protocol (generally described by the communication matrix) And can be easily tested with related equipment.
The recommended learning steps are:
1. Understand the basics of CAN
Through this ppt, Hengrun's things are still good.
CAN basis_百度文库
2. Intuitive understanding of CAN
This requires you to purchase or borrow CAN bus detection equipment, the grade is much worse. If you want to play, you can buy a weekly USB to CAN, Taobao is also a few hundred dollars. If it is a group purchase, you can buy a KCANer USBCAN, a few thousand. This is roughly the same.
If you have a local tyrant, you can buy Vector's VN1600, which is tens of thousands. I have used all three of the above. Be sure to buy a dual channel, then a mouth and a mouth, you can connect the extension cable to see the signal through the oscilloscope. Try to modify the message ID, data, baud rate, etc., to see the changes in the oscilloscope, to understand the content of the first part is very helpful.
There are three messages in this picture.
One bit is 2us, what is the baud rate of the bus? 1/2e-6=500Kbps
3. Select embedded platform to learn programming of CAN interface
Freescale MC9S08DZ60MLH 8-bit automotive grade CAN bus development board learning board super
You can choose this small board to practice, the program is written in the same way. It is then tested in conjunction with the second part of the bus detection device.
This step requires a detailed understanding of signal conversion knowledge, especially the difference between Big Endian and Little Endian, the role of factor and offset, how to set or set 0, you can refer to DBC_File_Format_DocumentaTIon_ Baidu library, very detailed, understand after reading.
4. If you are interested, you can look at the J1939 protocol (for commercial vehicles) or the CANOpen protocol (for field control, used by many motor controllers) or ISO 15031-5 (for OBD diagnostics).
Finally, I hope that after you understand CAN, don't spend too much energy on the bottom layer, basically physical labor. It is also the upper level that reflects the value. Please take a look at the relevant recruitment requirements of FAW Technology Center:
Job responsibilities
1. Design new energy vehicle network topology and develop network technology requirements;
2. Develop new energy vehicle network communication requirements, network communication matrix and network database;
3. Design and develop new energy vehicle network communication protocol simulation test, network communication specification, network harness specification;
4. Design new energy vehicle gateway controller and interface controller product definition and technical specifications with the same network communication function;
5. Responsible for solving problems in the process of electronic and electrical development of new energy vehicles, with production and after-sales service. Source: know almost Author: Wang Yu
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