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A controller area network (CAN) is a vehicle bus standard designed to enable efficient communication primarily between electronic control units (ECUs). Originally developed to reduce the complexity and cost of electrical wiring in automobiles through multiplexing, the CAN bus protocol has since been adopted in various other contexts.
A modern vehicle can have more than 70 ECUs that use CAN FD to exchange information over the CAN bus when the engine is running or when the vehicle is moving. On a CAN bus, a frame is the basic unit of messaging. For a classic CAN bus, a frame consists of an 11-bit identifier along with an 8-byte message payload.
In CANopen the 11-bit id of a CAN-frame is known as communication object identifier, or COB-ID. In case of a transmission collision, the bus arbitration used in the CAN bus allows the frame with the smallest id to be transmitted first and without a delay. Using a low code number for time critical functions ensures the lowest possible delay.
SAE J1939 defines five layers in the seven-layer OSI network model, and this includes the Controller Area Network (CAN) ISO 11898 specification (using only the 29-bit/"extended" identifier) for the physical and data-link layers. Under J1939/11 and J1939/15, the data rate is specified as 250 kbit/s, with J1939/14 specifying 500 kbit/s.
As defined in ISO 15765-4, emissions protocols (including OBD-II, EOBD, UDS, etc.) use the ISO-TP transport layer (ISO 15765-2). All CAN frames sent using ISO-TP use a data length of 8 bytes (and DLC of 8). It is recommended to pad the unused data bytes with 0xCC. The PID query and response occurs on the vehicle's CAN bus.
ISO 15765-2, [1] or ISO-TP (Transport Layer), is an international standard for sending data packets over a CAN-Bus. The protocol allows for the transport of messages that exceed the eight byte maximum payload of CAN frames. ISO-TP segments longer messages into multiple frames, adding metadata (CAN-TP Header) that allows the interpretation of ...
This can be information of all kinds and of different lengths such as Partnumber or the software version. Dynamic values such as the current state of the sensor can be queried. Each value is associated to a Data Identifier (DID) between 0 and 65535; for example, the VIN DID is 61840d (0xF190). Normal CAN signals are meant for information that ...
SocketCAN is a set of open source CAN drivers and a networking stack contributed by Volkswagen Research to the Linux kernel. SocketCAN was formerly known as Low Level CAN Framework (LLCF). Typical CAN communication layers. With SocketCAN (left) or conventional (right). Traditional CAN drivers for Linux are based on the model of character devices.