Controller Area Network (CAN)

Control Modules







The number of control modules in the CAN varies depending on the level of equipment, the car model and the structure week. The description applies to the structure week 199815-200149. The structure week and the manufacture week are not necessarily the same week. The week of manufacture is the week in which the car was manufactured in the factory. The content of the car is guided by the structure week A structure week can extend over many manufacture weeks. The structure week is specified in the format YYYYWW.

For example, the structure week 1998 15 indicates that the structure week of the car is week 15 1998.

Explanation

੘%:

��%:

�T�%:

"��%:

^ۙ%:

LS CAN = CAN Low speed section (125 Kbps)
HS CAN = CAN High speed section (250 Kbps)
Serial = Serial communication (Volcano Lite) between the slave control module and the Controller area network (CAN) control module (10.4 Kbps).
Slave control module = A control module with low computing power which is connected to a main "control module" and which only operates on commands from the main control module.
Option = Accessories installed at the factory to order, when purchasing a new car.
Accessories = After market installations.

The Network

General
- Increasing demands for further functionality in the car, both by statutory requirement and customers, have led to an increased complexity in the car.
- This has in turn driven the development of more flexible electronic systems. The Controller area network (CAN) is a result of this research. The network allows a large number of different commands and messages to be transmitted and received on the same cable. Previously each command or message required a separate cable. By using the network functionality has increased without increasing the number of cables.
- The number of commands and messages that can be handled by the network depends on the speed of the network and the length of the message/command. The Volvo network which is based on a Controller Area Network (CAN), can transmit over 500 different signals and approximately 100 messages (also known as frames). Each message can contain several signals, for example a message to the rear electronic module can contain all the signals for how the tail lamps should be lit.

Advantages of a network

Easier to add further functions and install accessories
Because the control modules in the network are already connected to each other and are easy to add more information to, all that is required is:
- to connect the sensors to the nearest control module
- to connect the controlled component to the nearest control module
- to download software to alter the configuration and programming of the network.

The length of the wiring and the number of components which are introduced with the car are less than previously.

An example of this is the addition of cruise control for the car.

Before the introduction of the network the installation of control modules, switches, vacuum pumps, vacuum servos, hoses and cable harnesses was necessary.

With the network only the installation of a switch and the downloading of software which alters the configuration of the car is required.

Easier to introduce logical functions
- Logical functions can be explained as "if this occurs then the following corrective action must be carried out". For example, the system is programmed so that if a tail lamp is broken, a message is transmitted via the Controller area network (CAN) to the driver information module to warm the driver.
- All that is required to introduce a logical function is to change the programming of the affected control module-the rear electronic module and driver information module in the example above.
- Introduction of logic functions does not increase the number of components or cables.

Easy to adapt the system to customer and market requirements
The functions can be altered depending on the requirements of the customer and market. An example of this could be fog tail lamps. Certain markets use two fog tail lamps, others only use one on the driver's side. Previously it was required that different replacement parts were stored for different markets. Now the same replacement part can be used for all markets, by changing the programming depending on the market.

Similar basic systems can be used for a whole model program
Similar networks (hardware) can be used for a large number of different cars.
The only thing which differentiates the cars is:
- the components (control modules, sensors controlled components etc.) which are connected to the system
- Which components do what
- Which components/functions are standard/optional/accessories
- The configuration/programming of the system

The Network Construction

General
The network is made up of a number of control modules (sometimes called nodes)which are connected to each other serially via two communication cables. Each control module is supplied with power and grounded individually and receives messages/commands via the two communication cables. In both networks (high and low speed sides) the control modules are serially connected. In the event of an open-circuit those control modules beyond the open-circuit will not be able to communicate with other parts of the network.

High and low speed sides on the network
The network consists of two parts. A high speed side which transfers (HS CAN) signals/messages between the central electronic module and the control modules in the engine compartment, and a low speed side (LS CAN) which transfers the signals/messages between the central electronic module and the control modules in the passenger compartment.

The interface between the high and low speed sides is supplied by the central electronic module which speeds up or slows down the communication between the two network sides.

Transfer speeds
The Volvo Controller area network (CAN) has two transfer speeds.
- HS CAN (High speed) has a transfer speed of 250 Kbps
- LS CAN (Low speed) has a transfer speed of 125 Kbps.

1 Kbps = 1024 bit per second (1byte = 8 bits).

For serial communication (Volcano Lite) between a control module and a slave control module the transfer speed is 10.4 Kbps. Terminating resistor To prevent electrical reflections and interference in the Controller area network (CAN) there are terminating resistors which bridge CAN H and CAN L. One in each end point on both the high and low speed side of the network. Each terminating resistor has a resistance of 120 ohm.
- The terminating resistor for the high speed Controller area network (CAN) is positioned in the brake control module/ABS control module and in the engine control module (ECM) or electronic throttle module. The terminating resistor is in the engine control module, on models without an electronic throttle module
- There are terminating resistors for the low speed Controller area network (CAN) in the upper electronic module and the rear electronic module.

Both the terminating resistors create a parallel circuit The following resistors can be measured under specified conditions:
- When the Controller area network (CAN) is intact the resistance in the network is approximately 60 ohm
- In the event of an open-circuit in the wiring, the resistance in the network is approximately 120 ohm
- In the event of a short-circuit between the communication cables the resistance is approximately 0 ohm.

The Controller Area Network (CAN)

General
CAN (Controller Area Network) is a standardized system for multiplex-communication. Volvo has developed a new standard for multiplex communication- VOLCANO. VOLCANO is a further development of CAN and operates with real time operation and prioritizing. The description of prioritizing is developed from VOLCANO but is designated CAN.

The standard for Control area network (CAN) specifies:
- That two cables should be used (CAN H and CAN L)
- Which voltage levels should be used
- What a message should look like
- How transfer errors should be handled. Cables, CAN H and CAN L

Cables, CAN H and CAN L







- The CAN H and CAN L cables must not be confused with HS CAN and LS CAN which are speeds on the Controller area network. CAN H and CAN L are a way of distributing signals within the multiplex communication network.
- Communication occurs through two cables. These two cables are paired together. CAN H is always white and CAN L is always green.
- The cables are made of copper and are easily identified by the green and white coloring.
- The voltage levels for communication occur using differential voltage levels.
- The reason for communicating using paired cables and differential voltage levels is that the network becomes less sensitive to interference.
- The same message is transferred simultaneously by both cables, but different voltage levels are used.
- Binary 0 = 2.5V both on CAN H and CAN L
- Binary 1 = 4V on CAN H and 1V CAN L.
- Average voltage level is 2.5V.

Controller area network (CAN) message







The message consists of the following components:
- Identifier ("flag"), which indicates the message identity and prioritization
- Data information (value, information etc.)
- Check sum, used to check that the message has arrived correctly
- Stop signal, which indicates that the message has finished.

A complete Controller area message is called a frame.

Prioritizing
- Conflicts can occur in a network when several control modules wish to send a message at the same time. For example when the driver presses the brake pedal at the same time as the passenger changes the climate control settings and a passenger in the rear seat opens the power window.
- For safe function the messages must be prioritized. In addition the time delays which occur in the event of a queue situation must be held with reasonable limits. This is so that the customer does not experience the system as slow.
- To solve problems with conflicts and time delays there is a priority order of messages to ensure good functionality.
- Prioritization of messages is determined by the number of zeroes at the beginning of a message, the more zeroes the higher the priority.
- Prioritization occurs as follows:
- When the network is available all the control modules with "something to say" send bit one in their message
- All the control modules detect what has been transmitted on the network
- If a control module has transmitted 0 those that have sent 1 stop and wait until the next time the network is available
- Those that transmitted 0 transmit bit two of the message
- If a control module has transmitted 0 as bit two those that have sent 1 stop and wait until the next time the network is available and so on.
- The message with the highest priority (most zeroes at the beginning) "wins" and is sent first.
- The end of a message is seven zeroes. The control modules then know that the network is available and a new message can be sent in priority order.

Two types of message
There are two types of message in the system:
- Periodical frames. These messages are sent regularly and give the present status of a parameter. They are used for information which is frequently updated, speed signals for example
- Event frames, which are only sent when predetermined conditions have been met. This type of message is used for things that seldom occur, raising/lowering a window for example.

The message can contain an update bit which states how "fresh" the information is.

The system assumes that the receiver has received the message so an acknowledgement is not sent (a reply is only sent to a direct question from another control module).

But the receiver knows how often it should receive a message about which status applies. If the message is missing the receiver can connect an emergency program and/or set a diagnostic trouble code.

Compatibility
- The units must "speak" the same language and must be compatible with each other. A standardized communication protocol is used for this.
- Signal configuration (sfg) contains the language between the units. If any module has a signal configuration which does not correspond to other units the module cannot communicate. This means that all the units must have compatible signal configuration. The signal configuration is occasionally modified so that the new messages are added and old messages removed.

Configuration
Instructions for the following are downloaded when a system is configured:
- Which control modules are included in the system (for example central electronic module, and others.)
- Which control module should do what (for example "you are the control module for the passenger door - you are the control module for the driver's door")
- Which functions should be included (for example if the alarm function should be on or off)
- Which components are connected to the control modules (for example whether the inclination sensor is included in the alarm or not)
- Which messages a control module is to transmit and which it is to receive
- Where the different data should be stored.

Configuration must be adapted to the installation of accessories and must be downloaded again after any control module is changed. Configuration is adapted and downloaded via VADIS.

NOTE: Even if two cars appear identical they may behave differently because of differing configurations, a parameter may have been modified by the customer or workshop.

Error Management In The Controller Area Network (CAN)

General
The Controller area network (CAN) is monitored and controlled by the central electronic module. When the central electronic module detects a fault in the controller area network a diagnostic trouble code (DTC) is set in the central electronic module. There are different diagnostic trouble codes depending on the type of malfunction detected.

Types of error which are handled are:
- Electrical faults
- No communication from the control module
- Faulty communication.

Electrical faults
- In the event of errors in the signal levels on the communication cables for the central electronic module a diagnostic trouble code (DTC) is stored in the central electronic module. A check is carried out on each communication cable to the central electronic module, CAN L, CAN H on the low speed side and CAN L and CAN H on the high speed side There are two different levels which are detected (low or high).
- This gives eight diagnostic trouble codes for detecting electrical faults.
- The diagnostic trouble codes for electrical faults are CEM-DF0X for the low speed network and CEM-DF1X for high speed network.

No communication from the control module
The central electronic module knows which control modules are in the Controller area network and checks that all the control modules communicate. If any control module on the Controller area network (CAN) does not communicate a diagnostic trouble code is stored in the central electronic module. There is a diagnostic trouble code for each control module. The diagnostic trouble codes are CEM-1A5X respectively CEM-1A6X.

Faulty communication
Each control module except for the central electronic module has two diagnostic trouble code types which are related to faulty communication (the central electronic module only has one type of diagnostic trouble code).

These are:
- Faulty messages
- Configuration fault (missing in the central electronic module (CEM)). Faulty messages When a control module sends errors in the messages a number of times, the control module stops communication. The diagnostic trouble code is stored in the control module which caused the faulty message. If the fault is permanent it is impossible to communicate with the control module. It is not possible to read off diagnostic trouble codes from the control module with the switched off communication.

The diagnostic trouble codes (DTCs) are XXX-E000 for the high speed network and XXX-E001 for low speed network.

Configuration fault
- If the signal configuration of a control module does not correspond to the signal configuration of the central electronic module, a diagnostic trouble code is stored in the control module with the faulty signal configuration.
- The diagnostic trouble code for configuration fault is XXX-E003.