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Mercedes C-ClassW203 since 2000 of releaseRepair and car operation |
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Mercedes-Benz + Mercedes-Benz Cars of a class C (W-203) + Operation manual + Routine maintenance + Engine + cooling and heating Systems + Power supply system and release + engine Electric equipment + Manual transmission + Automatic transmission + Coupling and power shafts + Brake system + Suspension bracket and steering + Body - Onboard electric equipment Specifications Diagnostics of malfunctions of onboard electric equipment - the general information Check of the electric motor of a screen wiper Check of warmed back glass Relay and safety locks Replacement of filament lamps of devices of external lighting Replacement of filament lamps of devices of internal lighting Removal and installation of the sensor of a daylight Removal and headlight installation Removal and installation of a fog light Removal and installation of a rasseivatel of a fog light Removal and installation of a back lamp Replacement of the battery of a key of an ignition/remote control Removal and installation of the electric motor of a cleaner of a windscreen Removal and installation of the electric motor of a cleaner of back glass Removal and installation of the tank of water and pump electric motor Removal and installation of the sensor of a rain Removal and installation of a sound signal Removal and installation of sensors of a parking Removal and installation of the sensor of temperature of external air Removal and installation of a control panel Removal and installation of the podrulevy switch Removal and installation of the switch of a forward plafond on a ceiling Removal and installation of group of switches to the left of a control panel Removal and installation of the switch of the central console Removal and installation of switches in the doorway Removal and installation of door switches of internal lighting Removal and installation of precautionary indexes of the assistant to a parking Removal and lighter installation Removal and radio receiver installation Removal and loudspeaker installation Digital tire of data of CAN The uniform lock - general information Installation of additional electric and electronic devices Appointment and arrangement of electric sockets + electric equipment Schemes |
Digital tire of data of CAN Data exchange on the tire CAN
Main data On the car some network tires of data exchange of CAN (Controller Area Network) between blocks (modules) of management of various systems and controlers of actuation mechanisms of the car are applied. Separate control units are incorporated with each other in the general network and can exchange data. The tire is two-forked, i.e. any device connected to it can accept and transfer messages. The signal from a sensitive element (sensor) arrives in the next control unit which processes it and transfers to the tire of data of CAN. Any control unit connected to the tire of data of CAN, can read out this signal, calculate on its basis value of the managing director of influence and operate an executive servomechanism. Advantages At usual cable connection of electric and electronic devices direct connection of each control unit with all sensors and executive elements from which he receives results of measurements or which operates is carried out. Complication of a control system brings to excessive length or large number of cable lines. In comparison with standard cable distributing the tire of data provides: · Reduction of quantity of cables. Wires from sensors last only to the next control unit which will transform the measured values to a package of data and transfers it in the tire CAN. · Operate the executive mechanism any control unit which on the tire CAN receives the corresponding package of data can, and on its basis counts value of operating impact on a servomechanism. · Improvement of electromagnetic compatibility. · Reduction of number of shtekerny connections and reduction of quantity of contact conclusions on control units. · Weight reduction. · Reduction of number of sensors since signals of one sensor (for example, from the sensor of temperature of cooling liquid) can be used by various systems. · Improvement of possibilities of diagnosing. Since signals of one sensor (for example, the signal of speed) are used by various systems in case the message on malfunction is issued by all systems using these signal, faulty is, as a rule, the sensor or the control unit processing its signals. If the message on malfunction arrives only from one system though this signal is used also by other systems, the cause of defect is concluded in the processing control unit or a servomechanism, more often. · High speed of data transmission – is possible to 1mbit/with at the maximum length of the line of 40 m. Now on and/m speed of data transmission makes Mercedes-Benz from 83 Kbps to 500 Kbps. · Some messages can serially be transferred on the same line. The tire of data of CAN consists of the strong wire executed in the form of twisted pair. All devices are connected to this line (control units by devices). Data transmission is carried out with duplication on both wires, and logic levels of the tire of data have mirror display (that is if on one wire level of logic zero (0) is transferred, on other wire level of logic unit (1), and on the contrary is transferred). The two-wire scheme of transfer is used for two reasons: for identification of mistakes and as reliability basis. If the peak of tension arises only on one wire (for example, owing to problems about EMS (electromagnetic compatibility)), blocks receivers can identify it as a mistake and to ignore this peak of tension. If there will be a short circuit or break of one of two wires of the tire of data of CAN, thanks to the integrated hardware-software system of reliability there will be a switching in an operating mode according to the single-wire scheme. The damaged transferring line will not be used. The order and format of messages transferred and accepted by users (subscribers) is defined in the data exchange protocol. Essential distinctive sign of the tire of data of CAN in comparison with other tire systems which are based on a principle of user's addressing, is the addressing correlated with the message. It means that on the tire of data of CAN its permanent address (identifier) marking the contents of this message (for example is appropriated to each message: temperature of cooling liquid). The protocol of the tire of data of CAN allows transfer to 2048 various messages, and addresses with 2033 on 2048 are constantly fixed. The volume of data in one message on the tire of data of CAN makes 8 bytes. The block receiver processes only those messages (packages of data) which are kept in its list of data of CAN of messages accepted on the tire (acceptability control). Packages of data can be transferred only if the tire of data of CAN is free (i.e. if after the last package of data the interval in 3 bits followed, and any of control units does not start to transfer the message). Thus logic level of the tire of data should be retsessivny (logic «1»). If some control units at the same time start to transfer messages, the priority principle according to which the message on the tire of data of CAN with the highest priority will be transferred to the first without loss of time or bits (arbitration of inquiries of access to the general tire of data) comes into force. Each control unit forfeiting the right of arbitration, is automatically switched to reception and repeats attempt to send the message as soon as the tire of data of CAN will again be released. Except packages of data there is also a package of request of a certain message on the tire of data of CAN. In this case the control unit which can provide a required package of data, reacts to this inquiry. Format of a package of data In a usual mode of transfer packages of data have the following configurations of blocks (frames): • Data Frame (a message frame) for transmission of messages on the tire of data of CAN (e.g.: temperature of cooling liquid). • Remote Frame (an inquiry frame) for request of messages on the tire of data of CAN from other control unit. • Error Frame (a mistake frame) all connected control units are notified that there was a mistake and the last message on the tire of data of CAN is void. The protocol of the tire of data of CAN supports two various formats of frames of the message on the tire of data of CAN which differ only on length of the identifier: - standard format; - expanded format. Now DaimlerChrysler uses only a standard format.
• Start of Frame (starting bit): Marks the beginning of the message and synchronizes all modules. • Arbitration Field (identifier and inquiry): This field consists of the identifier (address) in 11 bits and 1 control bit (Remote Transmission Request-Bit). This control bit marks a package as Data Frame (a message frame) or as Remote Frame (an inquiry frame) without bytes of data. • Control Field (operating bits): The management field (6 bits) contains IDE bit (Identifier Extension Bit) for recognition of a standard and expanded format, reserve bit for the subsequent expansions and - in the last 4 bits - number of bytes of the data put in Data Field (data field). • Data Field (this): The data field can contain from 0 to 8 bytes of data. The message on the tire of data of CAN in length of 0 bytes is used for synchronization of the distributed processes. • CRC Field (a control field): The field CRC (Cyclic-Redundancy-Check Field) contains 16 bits and serves for control recognition of mistakes by transfer. • ACK Field (reception confirmation): The field ACK (Acknowledgement Field) contains a signal of confirmation of reception of all blocks receivers which have received the message on the tire CAN without mistakes. • End of Frame (frame end): Marks the end of a package of data. • Intermission (interval): An interval between two packages of data. The interval should make not less than 3 bits. After that any control unit can transfer the following package of data. • IDLE (rest mode): If any control unit does not transfer messages, the tire CAN remains in a rest mode before transfer of the following package of data. Priorities For data processing possibility of their fast transfer should be in real time provided. It assumes not only line existence with high physical speed of data transmission, but also demands also operative providing access to the general tire CAN if it is necessary for several control units to transfer messages at the same time. For the purpose of differentiation of data of CAN of messages transferred on the tire on urgency degree, for separate messages various priorities are provided. The corner of an advancing of ignition, for example, has the highest priority, values of pro-slipping - average, and temperature of external air - the lowest priority. The priority with which the message is transferred on the tire CAN, is defined by the identifier (address) of the corresponding message. The identifier corresponding to smaller binary number, has higher priority, and on the contrary. The protocol of the tire of data of CAN is based on two logic conditions: Bits are or "retsessivny" (logic «1»), or "prepotent" (logic «0»). If the prepotent bit is transferred by at least one module, the retsessivny bits transferred by other modules, are rewritten. Example If some control units at the same time begin data transmission, the conflict of access to the general tire of data is authorized by means of «bit-by-bit arbitration of inquiries of the general resource» by means of the corresponding identifiers. By transfer of a field of the identifier the block transmitter after each bit checks, whether it possesses still the right of transfer, or already other control unit transfers on the tire of data of CAN the message with higher priority. If the retsessivny bit transferred by the first block transmitter is rewritten by prepotent bit of other block transmitter, the first block transmitter loses the right of a broadcast (arbitration) and becomes the block receiver.
The first control unit (N I) loses arbitration from the 3rd bit.
The elements connected to the fiber-optical tire D2B
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