Detailed explanation of the history of the OBD-II interface and how the EML327 reads car data through the OBD-II interface (Part 1)

Detailed explanation of the history of the OBD-II interface and how the EML327 reads car data through the OBD-II interface (Part 1)
EML327
The automotive OBD interface is based on the principles of the EML327 scan tool, what components and principles are in it, what are the general standards for the operation of these scans and what is OBD2? OBD was developed in 1986 and OBD-II was developed in 1996.
OBD Port

Standards for OBD and OBDII
Although standards have been defined for the OBD and OBD2 interfaces, many car manufacturers have not changed the interface standards, starting with the use of a uniform interface by automotive regulators for the period. Convincing automotive self-diagnosis systems, what does automotive self-diagnosis have to do with OBD? The regulation has also made a definite instrument for the corner position of the car connector. The following diagram.

OBD2 interface definition

J1962 connector and OBDII communication protocol
The standard of OBDII interface is SAEJ1962 standard, and the protocol of each foot position is fixed, the protocol of the 2nd foot is J1650+ the 10th foot is J1650-, currently the first two protocols are used by Ford and Mazda, the second protocol is used by Gengral Motors, there is still huge space for other corner positions. The protocol 15765 that we have seen in recent years has 45250 specific bits available, but the more troublesome 29-bit identifier, CAN LOW, was used in 2008, and since 2008 all new cars sold have been required to have a CAN bus. It is divided into two protocols, ISO14230 (KWP2000), which is used by BMW, VA6 and other cars. These protocols are difficult to unify by all car manufacturers, so three of the most popular protocols are left, and they are arranged and integrated into a 16-pin arrangement. Car diagnostics can be made using 2 pins, pin 7 and pin 15, and the reconstructed standard makes protocols for 3 any contacts. To make signatures for three pins, it is contact 1, 3 and 9 that are made as signatures for each manufacturer. For the other pins the manufacturer has the definitions for them reduced and protocols that are not available can be left out, obviously different brands have different definitions. However, these protocols are generally covered. In total there are 5 commonly used protocols and only 9 protocols are used in total. As long as the car testing equipment can read the 9 protocols it can test over 90% of the cars on the market.
Automotive protocol working with EML327
How OBDII automotive diagnostic devices are arranged in hardware
There are clear standards for regulated protocols and humans have to work from 5 protocols, firstly you need to convert the protocols to read from the COM port either using USB or Bluetooth or WIFI depending on what device you are using. To read this information, we can use a computer, tablet or mobile phone to display it.
The conversion of the car's internal data is carried out separately from the COM port. There is usually a middleware link to the controller. In practice the COM port is not present, the interface is USB or we use a PC or mobile phone, for these devices to communicate easily a special chip is required to convert the data to the car.
For wireless connection, there is usually a Bluetooth module or a WIFI module, so that the data can be read out wirelessly, generally the device only needs to read out 5 protocols to work properly.

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