A CAN Bus: What is it? An Overview of Networking in Vehicles
The Transition to a Centralized Network from Point-to-Point Wiring
In the past, automotive electrical systems were built similarly to home wiring, with a specific heavy-gauge wire connecting each switch to each individual component—one for the horn, one for the power windows, one for the headlights, and so forth.27 As the number of electronic features increased and multiple Electronic Control Units (ECUs) were introduced for things like airbags, engine management, and anti-lock brakes, wiring complexity skyrocketed in the 1970s and 1980s. A more sophisticated and efficient communication system was required as a result of the thousands of separate wires that were added to vehicles, increasing their weight, cost, and potential sites of failure.27 This complexity was exacerbated by the need to reduce weight in order to improve fuel economy.
The German firm Robert Bosch, working with industry partners, came up with a solution in the middle of the 1980s: the Controller Area Network, or CAN bus.27 This protocol, which was first made available for purchase in the late 1980s, transformed automotive electronics by substituting a lightweight, straightforward two-wire serial bus for the heavy point-to-point wiring harness.
How the CAN Bus Operates: A Protocol Based on Messages
All the electronic modules, or “nodes,” are connected to this common two-wire bus (CAN High and CAN Low). The CAN bus is a message-based protocol that enables all the different ECUs and electronic devices within a vehicle to communicate with each other in a dependable and effective manner without the need for a central host computer.
Each node broadcasts its data into the network in standardized packets known as “frames” rather than transmitting signals directly to each other.27 Each frame is received by every other node on the network. In addition to the data (for example, “engine speed is 2500 RPM”), the frame also includes an identification that defines the message’s content and gives it a priority level.
Bitwise arbitration, the CAN protocol’s technique for managing simultaneous transmissions, is a crucial component. The node with the lower-value (and thus higher-priority) identifier will win arbitration and continue to transmit without interruption or data loss if two nodes attempts to broadcast a message simultaneously.27 The other node will cease transmission and wait for the bus to become available again. For safety-critical applications, this priority-driven method is crucial because it guarantees that an ABS module message about wheel lockup always takes precedence over a temperature control system message that is less important.
The CAN Message Frame’s Structure
The most often used frame type for data transmission on the CAN system is the Data Frame. A typical data frame has a number of important fields:
The message identification is included in the arbitration field, which also establishes the message’s bus priority.
Data Field: Up to 8 bytes of the actual data being sent are included here.
Cyclic Redundancy Check, or CRC Field: is an error-checking feature that enables receiving nodes to confirm the message’s integrity.
Receiving nodes use the acknowledgement field to indicate that they have successfully received the message.
Because of its sturdy design and integrated error detection and prioritization mechanism, the CAN bus is incredibly dependable and impervious to the electrical noise and electromagnetic interference (EMI) that are typical in an automotive setting.
The CAN Bus System’s benefits:
The worldwide automobile industry has adopted the CAN bus standard because it offers several important benefits over conventional wire systems 27.
Simplicity and Weight Loss: The most obvious advantage is the significant weight reduction. A single twisted-pair cable replaces kilometers of expensive, complicated wire, thereby decreasing vehicle weight and improving fuel efficiency. This also makes manufacturing and assembly easier.
Low Cost: The system is very cost-effective due to the use of a single, shared bus and easily accessible, reasonably priced CAN controller chipsets.
Centralized Diagnostics: The OBD-II port on the CAN bus serves as a single point of access for all linked ECU communication. This enables personnel to use a single tool to diagnose, configure, and record data from the complete vehicle network.
Extreme Robustness: The protocol is very durable to electrical disturbances due to its differential signaling (using CAN High and CAN Low lines) and comprehensive error-checking capabilities. This is crucial for safety-critical devices like stability control, airbags, and brakes.27
Flexibility and Efficiency: Priority-based messaging guarantees that important information is always sent promptly. Furthermore, it is not necessary to completely rewire the vehicle in order to add new electrical features or nodes to the network; they may simply be linked to the current bus.
The CAN bus essentially serves as the modern vehicle’s central nervous system, facilitating the smooth and dependable communication required for the intricate interactions between safety, comfort, and performance systems that characterize current automotive technology.
