Rede de comunicação – Visão geral

418-00-6 Module Communications Network 418-00-6 DESCRIPTION AND OPERATION Terminating resistor In order to avoid reflections and interferences in the CAN bus network, a terminating resistor is provided for bridging purposes at both ends of the CAN. Each terminating resistor has a resistance value of 120 Ohm. ‡ For the HS CAN bus, the terminating resistors are located in the body control module (BCM) and in the powertrain control module (PCM). ‡ For the MS/MM CAN bus, the terminating resistors are located in the body control module (BCM) and in the electronic instrument cluster. The two resistors are connected in parallel. The resistance values are as follows: ‡ When the CAN bus is intact, the resistance is approx. 60 Ohm in both areas of the network. ‡ In the event of a short circuit between the communication lines the resistance is approx. 0 Ohm. Controller Area Network (CAN) Standard General The CAN bus is a standardized system for multiplex communication. This means that multiple control modules can use the same wires for communication without causing interference between the different signals. The Controller Area Network (CAN) Standard specifies the following: ‡ The use of two wires (CAN H and CAN L) ‡ The voltage amplitudes ‡ The structure of the messages ‡ The way in which transmission faults are handled The lines CAN H and CAN L The lines CAN H and CAN L must not be confused with the different data transfer rates HS CAN bus and HS CAN bus. The lines CAN H and CAN L are the paths on which signals are transmitted within the multiplex communication system. Communications take place at different voltages via two separate wires which are twisted in pairs. As a result, the network is less susceptible to interference. The same message is put out at the same time on both wires with different voltages. ‡ Binary signal 0 2.5V on CAN H and on CAN / ‡ Binary signal 1 4V on CAN H and 1V on CAN / The average potential difference between CAN L and ground is approx. 2.3V, or approx. 2.8V between CAN H and ground. These measured values refer to "normal" communications in the Controller Area Network (CAN), i.e. cases in which no faults have occurred which would cause the modules to send out error messages. NOTE: Certain modules, such as the restraints control module (the module for the SRS system) and the ABS module or ESP module communicate with their relevant sensors via a so-called internal CAN bus. The internal CAN bus systems have nothing to do with the communications on the general CAN bus. Instead, they are only used for the purpose of transmitting data between sensors and associated modules.