How to develop a standard car OBD2 diagnostic procedures

Development standards OBD2 diagnostic procedures to prepare the information and hardware
1, due to TL718 has created for you the physical layer, data link layer and part of the application layer protocol, so long as the OBD2 standard application layer protocol text, ISO15031-5 or SAE J1979 (two protocols are the same content).
2, TL718 diagnostic interface or a set of self-built circuit TL718 chip.
3, home PC, a computer desk.
4, install the software: Accessport debugging software and VC + + (or VB, BC + +, etc.) your favorite software development.
5, symbol OBD2 standard automotive engine computer one (or a car)

TL718 Information

TL718 with the microcontroller via a UART serial port, PDA, or PC RS232 communications, in some new equipment on a PC has no RS232 serial port, through a virtual serial port can communicate with the TL718, for example, USB TO RS232, Ethernet TO RS232, or Bluetooth TO RS232 and so on.

No matter what kind of physical connection, you can use HyperTerminal or serial debugging tools, send and receive directly from the keyboard character. When using serial debugging software, you must first set the correct COM port number and the correct baud rate. Typically 9600 baud (PIN6 = 0V), or 38400 baud (PIN6 = VCC, PP OC set default values​​). Serial port settings are: 8 data bits, Parity: 0, 1 stop bit. If set incorrectly, and TL718 will not communicate properly. All responses from the TL718 with a carriage return (0X0D) and an optional newline (0X0A) ends. Properly connected, turn on the power. TL718 will drive the test LED lights (flashes three times), send:

TL718 starting
If the correct receipt of the above information represents the serial port and connection settings are correct. The second line ">" symbol represents TL718 is idle, you can immediately receive data from RS232. If you do not receive a ">" symbol to send data to the TL718 may cause data loss. Incorrect response occurs. PC from the serial port to send commands to the TL718 format:
TL718 has two kinds of formatting commands
1, OBD connect command, a communication with the vehicle.
2, the internal command, all beginning with AT, do not communicate with the vehicle occur
send must 0x0d (carriage return) terminated ASCII characters carriage return character is behind TL718 discarded.
TL718 internal command "AT" at the beginning, followed by visible characters. Invisible characters and spaces are ignored attached.
OBD command can contain only ASCII code in hexadecimal (0-9, af, AF), spaces are ignored.
If you send a command that can not be effectively interpreted TL718, TL718 will return a "?" Indicates that the send command is invalid.
When processing OBD commands TL718, TL718 continuously monitors the RTS pin and RS232 input, any of which happens, TL718 will interrupt the current OBD commands, making it quick return to the prompt ">", waiting to receive a new command.
TL718 uppercase and lowercase characters can be received, spaces are ignored. Analogy command "ATZ", "atz", "at z" are the same.