Computers/Controls - CAN Systems Information

CAN Systems

Automotive communications is a way for on board components to talk to each other. Current vehicles use a system of vehicle communication called networks to provide higher performance and increased levels of safety. By using networking, Hyundai vehicles are able to operate with a significant amount of sensor and actuator interaction, while actually reducing the total amount of wiring. The system uses networking to share common information.

The Controller Area Network (CAN) system was developed by the Robert Bosch Company. Today, Hyundai vehicles have multiplex systems based on CAN networks. Multiplexing is a system which connects onboard computers, or control modules that allows them to interact by transmitting multiple messages through the same circuit. Various control modules can transfer data back and forth at rapid speeds and multiple control modules can share the same sensor information simultaneously. Each computer can send information over the system and determine what information to take in from the system ignoring what it does not need. Beginning in the 2008 model year, all Hyundai vehicles will utilize CAN systems.

The CAN offers two speeds of communication called "high speed" and "low speed". High Speed communications relate to more critical sensor and actuator activities.





For example, a safety-related signal would be processed through the CAN while a climate control signal would be handled at low speed. High speed is used for both safety and performance functions handled by the ECM, PCM and ESC, if equipped. Multiplexing uses digital communication made up of binary code. Binary refers to signals that contain a value of either -0- or -1- also called bits. The 1 is indicated by a voltage that is above a threshold value, while a 0 is represented by a voltage below the threshold. Binary "words" are made up of a combination of the two values. A word with eight bits constitutes a byte. (See Figure 1)





In the on-board network, control modules gather data from several sensors and actuators. The data is then assessed and responses are transferred through just one set of single or dual communication lines between the various control modules. This reduces the need for individual wires to run over the entire length between a switch and the load. (See Figure 2.)

Other advantages from using CAN systems are notable. The reduced need for wiring means less connectors and reduced size for wiring harnesses. This in turn creates greater system reliability since there are less components and connectors. Less wiring also reduces the cost and makes the whole communication system more flexible for additions and design.

There are two types of automotive communication systems used on Hyundai vehicles. They are a serial communication also called K-Line in Hyundai's ETM and the CAN system which is a parallel system. Serial data communication means that there is one data transmitting line and all data bits are sent in series one message at a time. This mode is one-directional. Serial systems are slower than parallel systems. Lower cost and diagnostic simplicity makes serial communication systems preferable in some instances.

Parallel communication allows the same message or data to travel to multiple devices at the same time. Since this form of communication is faster it is more efficient. The CAN system uses two connectors in parallel from each module; and a signal is sent out over both lines at the same time. This provides redundant signals. If there is an issue with one line the other can operate the circuit. The high speed CAN signal uses a base voltage of 2.5V.





This is binary code for -1-. When the voltage goes above 3.5V on the high line and below 1.5V on the low line the binary code for -0- is indicated. The high and low lines will mirror each other. Note: High line and low line refer to the redundant communication lines in CAN and should not be confused with the high speed and low speed communication functions in the CAN system. (See Figure 3.)

Since the voltage range between the high and low lines of the high speed and low speed CAN systems is narrow the system protects the signals from interference from nearby circuits. This is accomplished with a grounded insulating shield surrounding the twisted wiring used in the CAN system. After a signal has been read by each control module it must be removed from the CAN system. So at the end of the CAN lines there

Note:
CAN-H and CAN-L represent the redundant wiring are terminating resistors. The resistors also compensate for varying distances between Control Modules and the resulting variances in resistance. These resistors can be located externally on the harness or inside a Control Module.

How does CAN work? The CAN system encodes each data or action request in the module as a signal. The first part of the signal is a unique identifier for the signal. Then the module checks to see if there is already a signal on the wire. If the CAN is available the module sends the signal. Each module checks to see if the message is relevant, and if it is, the module processes it accordingly. If the signal is not relevant to the module's function, then it is ignored.

The signal identifier determines the type of signal and the priority that the signal should be given. If two signals are transmitted at the same time, the higher priority is allowed to be transmitted first. The lower priority signal will be transmitted in the next cycle of messages. The process of determining the priority of messages is called "arbitration."





On some models such as the Entourage and 2008 Azera, both CAN and a Local Interconnect Network (LIN) are used with the Body Control Module. The LIN is a serial network; so communication moves in only one direction and is slower than CAN communication. LIN uses a signal that toggles between 0V and 12V. The table below contrasts the Controller Area Network and the Local Interconnect Network.

CAN vs. LIN

This article has shown a simple overview of the CAN system components and operation. For additional information on related trouble codes and CAN diagnosis, check out the CAN web course found at hmatraining.org. You will need to register and log in to the recently revised site, so look for instructions elsewhere in this issue.