Rede de comunicação – Visão geral

418-00-8 Module Communications Network 418-00-8 DESCRIPTION AND OPERATION ‡ Periodic signal frames are sent regularly to indicate the current status of a parameter. They are used for types of information which change frequently, e.g. vehicle speed signals. ‡ Event-related signal frames are only sent if certain conditions are met. They are used for types of information which occur more rarely, e.g. the opening or closing of a window. The messages may also incorporate an update bit which shows how "new" the message is. The system always assumes that the messages reach the intended recipient, so no receipt acknowledgement signals are sent out. Replies are only sent in response to direct queries from other modules. However, a receiver module also knows how often it should receive a particular status message. If the message is not received then the receiver module can launch an emergency running program and/or set a trouble code (DTC). Compatibility The modules must all speak the same language and be compatible with each other. As a result, a standardized communication protocol is used. The language of the modules is contained in the signal configuration. If the signal configuration of a module does not match the configuration of the other modules than the module cannot communicate with them. This means that all modules must have a compatible signal configuration. In order to check this, the body control module (BCM) sends out an identification number for its signal configuration via the Controller Area Network (CAN). The other modules compare this number to their own number. If the identification does not match then the module stores a trouble code (DTC). The signal configuration is changed occasionally, so that new messages are added and old ones are removed. Configurations The following information is downloaded when a system is configured: ‡ Type of control modules contained (e.g. body control module (BCM)) - task assignments for the individual modules (e.g. this is the module for the driver's door)) ‡ Functions contained (e.g. alarm function on or off) ‡ Connected components (e.g. whether or not the inclination sensor is relevant for the alarm function) ‡ Output an input messages for each module ‡ Storage locations for various data The configuration needs to be adapted for any accessories which are installed and needs to be downloaded again if a module is replaced. The diagnostic unit is used for adaptation and downloading. NOTE: Two vehicles which otherwise appear identical may behave differently if they have different configurations. Parameters may have been changed by the customer or by the workshop. Error management in the Controller Area Network (CAN) General The Controller Area Network (CAN) is monitored by the body control module (BCM). If the BCM detects a fault in the CAN bus then a trouble code (DTC) is stored in the BCM. There are different types of DTC according to the fault type: ‡ No communications from the module ‡ Faulty communications No communications from the module The body control module (BCM) knows which modules are in the Controller Area Network (CAN) and checks whether all modules are communicating. If a module is not communicating a trouble code (DTC) is set in the BCM. There is a trouble code (DTC) for every module. Faulty communications If the Controller Area Network (CAN) is in operation then the body control module (BCM) continuously monitors the flow of information in the network. If the BCM determines that, for some reason, the communications in the CAN bus are interrupted, it can set a trouble code (DTC). The BCM has trouble codes for all parts of the CAN bus (one each for the HS CAN bus and the MS/MM CAN bus).