In this example the engine speed input from the crankshaft position sensor to the engine ECM is also required by the Instrument cluster for the tachometer. The diagram below illustrates how a message received by the engine control module is processed and transmitted on the network for other modules. A component such as a throttle motor will still require supplies, grounds and feedback signals as with a non-CAN vehicle.
Note: Inputs and outputs to a module are still analog. The CAN transceiver converts the binary data into a voltage range and this is the signal voltage observed on the network. The CAN controller converts data (binary) sent from the microprocessor and sends it to the CAN transceiver. A transceiver has the ability to both transmit and receive data. Signal GenerationĮach module on the network has a CAN controller and a CAN transceiver on the CAN chip. These are referred to as terminating resistors.Īll these characteristics will be described in greater detail below. To ensure optimum signal quality, two fixed value resistors are connected to the bus to condition the signal. To ensure messages of the highest priority are transmitted first, an arbitration field is part of the message structure.
That’s 500,000 pieces of data or information per second!! The signal is broadcast over two communication wires to ensure signal integrity is maintained, these wires are twisted together and are referred to as CAN High and CAN Low. The data transfer rate is 500K bits/sec for high speed CAN. Multiple modules are connected to the bus in parallel. Characteristics of a high speed CAN network (Class-C)
This article will provide the technician with the necessary tools to successfully validate a CAN bus signal and help to identify faults where present.īasic block diagram of a typical CAN Network. Troubleshooting such a complex system is reasonably straightforward once the technician has a basic understanding of the network and how data is transferred. This has the benefit of reducing vehicle wiring and allowing additional vehicle options to be added or removed easily. Controller Area Network (CAN) is a data transfer network designed to allow many nodes (modules) to communicate using a standard structure and format.
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