Rede de comunicação – Visão geral

418-00- Module Communications Network 418-00- DESCRIPTION AND OPERATION With the exception of the BCM, which only knows one type of DTC, each module uses two types of DTC in relation to communication faults. These are: ‡ Faulty messages ‡ Faulty configuration As the BCM is the main module in the network, it does not have a DTC for faulty configuration. Faulty messages The control modules continuously monitor the flow of information in the Controller Area Network (CAN). If a module receives a message it cannot interpret it sends a fault message via the CAN bus. The modules also have function which allows them to detect any faulty messages they generate themselves. This prevents interference on the CAN bus. If there is a lot of interference in the network then any modules which cannot communicate properly can switch themselves off. This status is referred to as "databus OFF" - the module can no longer send or receive information. To prevent the vehicle from coming to a sudden standstill or suffering a total loss of particular functions if a fault occurs in the CAN bus, certain modules have an emergency running mode. This means that modules which are required for driving or for safety aspects (e.g. the powertrain control module (PCM) or the transmission control module (TCM)) can maintain a restricted functionality on the basis of predefined or estimated data. For example, if communications to the transmission control module (TCM) are interrupted then the transmission will use a preselected gear which will enable the customer to at least drive to the nearest workshop. A module remains in "databus OFF" mode until the power supply to the module is switched off, or a module determines that the "databus OFF" condition no longer exists. If the power supply is reconnected the module attempts to re-establish communications. Faulty configuration The body control module (BCM) transmits its configuration ID within the messages it sends out to other modules. To enable the modules in the Controller Area Network (CAN) to communicate with each other they must have the same configuration ID, as modules only look at messages carrying their own configuration ID. If the signal configuration of a module does not match the signal configuration of the BCM then a trouble code (DTC) is stored in the module with the faulty configuration. NOTE: A module will save a trouble code (DTC) if it does not receive any messages from the engine control module (ECM). This also applies if there are any software errors in the module. If the circuit in the Controller Area Network (CAN) is interrupted then certain modules will also not receive any messages from the ECM. NOTE: A module will save a trouble code (DTC) if it does not receive any messages from the body control module (BCM). This also applies if there are any software errors in the module. If the circuit in the Controller Area Network (CAN) is interrupted then certain modules will also not receive any messages from the BCM. Local Interconnect Network (LIN) The Local Interconnect Network (LIN) bus is a standard which has been developed for cost-effective communications between intelligent sensors and actuators in motor vehicles. LIN is used wherever the bandwidth and versatility of CAN is not required. The LIN specification comprises the LIN protocol, a standard format for describing a complete LIN network and the interface between a LIN network and the application. A LIN network is made up of a LIN master and one or more LIN slaves. The LIN network utilizes the master/slave principle for the purpose of bus access control. This has the significant advantage that few resources (CPU performance, ROM, RAM) are required for bus management in the slave module. The master is implemented in a control module or a gateway which has the necessary resources. All communication is initiated by the master. Consequently, a message always consists of a header, which is generated by the master, and a response from the slave. The data transfer rate is in the region of up to 20 Kbit/s. The LIN master knows the time sequence of all data which are to be transmitted. These data are transmitted by the corresponding LIN slaves (e.g. ultrasonic sensors) when requested to do so by the LIN master. LIN is a single-wire bus, i.e. the data are transmitted across a single-stranded cable. Usually the same cable is also used to provide the supply voltage. The ground connection of the supply voltage also acts as the ground connection of the