NOT controler is intended connections to onboard systems of self-diagnostics of the first generation (OBD I)!
For connection to the computer (RS) it is enough 3-жильного a wire, connection to the diagnostic socket is carried out 6-жильным by a wire. The supply voltage moves on the controler via the 16-contact diagnostic OBD socket.
The free software (browser) for reading of codes and data can be downloaded from sites of producers, or a site of our publishing house (arus.spb.ru), and is intended for use under DOS. The insignificant size of a program application in option В«under DOSВ» allows to contain it on the loading diskette DOS and to use even on the computers equipped with the software incompatible with DOS. An unessential condition is even existence in the computer of a hard disk.
If the opposite is not stipulated especially, all numbers are given in a 16-richny format (hex), the decimal format is designated by well-aimed dec.
At this stage protocol initialization on which data exchange will be made, and in case of the ISO protocol - initialization of onboard system is made. Data exchange is made on one of three protocols: VPW (General Motors), PWM (Ford) and ISO 9141-02 (the Asian/European producers).
There is a set of exceptions: so, for example, at poll of some models of Mazda cars the fordovsky PWM protocol can be used. Thus, at emergence of problems of transfer it is necessary first of all to try to use any other protocol.
The choice of the protocol is made by transfer of the combination consisting of control byte of 41 (hex) and byte following directly it, the protocol defining type: 0= VPW, 1 = PWM, 2 = ISO 9141. So, for example, at the command of 41 (hex) 02 (hex) ISO 9141 protocol initialization is made.
In reply the controler sends control byte and condition byte. The MSB installation of control byte speaks about existence of the problems, the byte of a condition thus following it will contain the relevant information. At successful initialization the control byte of 01 (hex) specifying is sent that the verifikatsionny byte of a condition further follows. In case of the VPW and PWM protocols the verifikatsionny byte represents a simple echo of byte of a choice of the protocol (0 or 1, respectively), at ISO 9141 protocol initialization it will be the digital key returned by the onboard processor and defining which of two versions of the protocol slightly differing from each other will be used.
It is necessary to notice that initialization of the VPW and PWM protocols occurs much quicker as demands only transfer of the relevant information to the controler. On the models answering to the ISO standard, initialization takes about 5 seconds, spent for a controler exchange of information with the onboard processor, the 5th baud made with a speed. It is necessary to pay attention of the reader that on some models of cars of ISO family 9141 initialization of the protocol stop, if the request for issue of data is not transferred during a 5-second interval, - told means that PC should make automatic delivery of inquiries everyone some seconds, even in a single mode.
The ISO 9141-2 standard is used by the majority of Asian and European producers of automobile equipment. The structure of formed PC of inquiry a little than differs from used in the SAE standards with that only a difference that the controler does not need information on number of a shot and the relevant information to be present at a package should not. Thus, the inquiry always consists of control byte and a chain of the information bytes including checksum following it. As the response message the controler simply relays the signals created by the onboard processor. The control byte in the response message is absent, therefore PC perceives arriving information continuously until the chain does not interrupt the pause the in length of 55 milliseconds reporting about end of information package. Thus, the response message can consist of one or more shots according to requirements of the SAE J1979 Specifications. The controler does not make the analysis of shots, does not reject not diagnostic shots etc. PC should make own forces processing of arriving data with the purpose of exarticulation of separate shots by the analysis of heading bytes.
ISO 14230 protocol support is added.
If controler use for data transmission only on any to one is planned or to two of protocols, superfluous components can be excluded (see the scheme above). For example, at the scheme organization under the VPW (GM) protocol in a wire of connection of the controler to the car three veins of electroconducting (plug 16, 5 and 2) be required only.