Modern cars are increasingly adapting to the specific needs of people. They have many additional systems and functions that are associated with the need to transfer certain information. If separate wires had to be connected to each such system, as it was before, then the entire interior would turn into a continuous web and it would be difficult for the driver to control the car due to the large number of wires. But the solution to this problem was found - this is the installation of a Can-bus. What role the driver will be able to learn now.
Can bus - does it have anything in common with conventional tires and what is it for
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Hearing such a definition as "CAN tire", an inexperienced driver will think that this is another type of car rubber. But in fact, this device has nothing to do with ordinary tires. This device was created so that there was no need to install a bunch of wires in the car, because all machine systems should be controlled from one place. Can bus makes it possible to make the car interior comfortable for the driver and passengers, because if it is present, there will not be a large number of wires, it allows you to control all car systems and connect additional equipment in a convenient way - trackers, alarms, beacons, secrets and more. The old-style car does not yet have such a device, which causes a lot of inconvenience. The digital bus does a better job with the tasks assigned to it, and the standard system - with a bunch of wires, is complex and inconvenient.
When was the digital CAN bus developed and what is its purpose
The development of the digital bus began in the twentieth century. Two companies, INTEL and BOSCH, took responsibility for this project. 
After some joint efforts, the specialists of these companies developed a network indicator - CAN. It was a new type of wired system through which data is transmitted. This development was called a tire. It consists of two twisted wires of a sufficiently large thickness and all the necessary information for each of the car's systems is transmitted through them. There is also a bus, which is a bundle of wires - it is called parallel.
If you connect a car alarm to the CAN bus, then the capabilities of the security system will increase, and the direct purpose of this car system can be called:
- simplification of the mechanism for connecting and operating additional vehicle systems;
- the ability to connect any device to the car system;
- the ability to simultaneously receive and transmit digital information from several sources;
- reduces the influence of external electromagnetic fields on the performance of the main and additional vehicle systems;
- speeds up the process of transferring data to the necessary devices and systems of the machine.
To connect to the CAN bus, you need to find orange in the wire system, it must be thick. It is to it that you need to connect in order to establish interaction with the digital bus. This system works as an analyzer and distributor of information, thanks to which the high-quality and regular operation of all vehicle systems is ensured.
Can bus - speed parameters and data transfer features
The principle of operation on which the CAN bus analyzer operates is that it needs to quickly process the information received and send it back as a signal for a specific system. In each individual case, the data transfer rate for vehicle systems is different. The main speed parameters look like this:
- total speed of data streams transfer via digital bus –1 Mb/s;
- the speed of transfer of processed information between the control units of the car - 500 kb / s;
- the rate at which information is received by the Comfort system is 100 kb/s.
If a car alarm is connected to the digital bus, then information from it will come as quickly as possible, and the commands given by the person, using the key fob, will be executed accurately and on time. The system analyzer works without interruption and therefore the operation of all machine systems will always be in good working order. 
A digital bus is a whole network of controllers that have united into one compact device and are able to quickly receive or transmit information, starting or turning off certain systems. The serial mode of data transfer makes the system work more smoothly and correctly. The CAN bus is a mechanism that has the Collision Resolving access type and this fact must be taken into account when installing additional equipment.
Can there be problems in the operation of the bus
Kan bus or digital bus works with many systems at the same time and is constantly engaged in data transfer. But as in every system, failures can occur in the CAN bus mechanism and the information analyzer will work extremely incorrectly from this. Canbus problems can occur due to the following situations:
When a system malfunction is detected, it is necessary to look for the cause of this, given that it may be hiding in the additional equipment that was installed - car alarms, sensors and other external systems. Troubleshooting should be done in the following way:
- check the operation of the system as a whole and request a fault bank;
- checking the voltage and resistance of conductors;
- checking the resistance of the resistor jumpers.
If there are problems with the digital bus and the analyzer cannot continue to work correctly, do not try to solve this problem yourself. For competent diagnosis and performance of the necessary actions, the support of a specialist in this field is necessary.
What systems are included in the modern Can bus car
Everyone knows that the can bus is an information analyzer and an accessible device for transmitting commands to the main and additional vehicle systems, additional equipment - car alarms, sensors, trackers. The modern digital bus includes the following systems:
This list does not include external systems that can be connected to the digital bus. In place of such there may be a car alarm or additional equipment of a similar type. You can receive information from the CAN bus and monitor how the analyzer works using a computer. This requires the installation of an additional adapter. If an alarm and an additional beacon are connected to the CAN bus, then you can control some car systems using a mobile phone for this.
Not every alarm has the ability to connect to a digital bus. If the owner of the car wants his car alarm to have additional features, and he could constantly control the systems of his car at a distance, you should think about buying a more expensive and modern version of the security system. Such an alarm is easily connected to the CAN bus wire and works very efficiently.
CAN bus, how a car alarm is connected to a digital bus
The digital bus analyzer copes not only with the internal systems and devices of the car. Connecting external elements - alarms, sensors, other devices - adds more load to the digital device, but at the same time its productivity remains the same. A car alarm that has an adapter for connecting to a digital bus is installed according to a standard scheme, and in order to connect to CAN, you need to go through a few simple steps:
- The car alarm is connected to all points of the car according to the standard scheme.
- The owner of the vehicle is looking for an orange, thick wire - it leads to a digital bus.
- The alarm adapter is connected to the car's digital bus wire.
- The necessary fixing actions are carried out - installing the system in a safe place, insulating wires, checking the correctness of the process.
- Channels are configured to work with the system, a functional range is set.
The possibilities of a modern digital bus are great, because a coil of two wires combines access to all the main and additional vehicle systems. This helps to avoid the presence of a large number of wires in the cabin and simplifies the operation of the entire system. The digital bus works like a computer, and this is very relevant and convenient in the modern world.
Every year, automotive electrical circuits have increased in size and become more complex in design. On the first cars produced, the ignition worked from the magneto, but there was no battery and generator at all. The headlights used acetylene torches.
In 1975, the length of wires in an automobile electrical circuit was several hundred meters and was comparable to the electrics of a light aircraft.
The desire to simplify the wiring was as follows: only one wire is needed, connect all consumers to it and connect a control device to each. Pass through this wire an electric current to consumers and control signals for devices.
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By 1991, thanks to a breakthrough in digital technology, Bosch and Intel created a CAN (Controller Area Network) network interface for multiprocessor on-board computer systems. In electronics, such a system is called a "bus".
In a serial bus (serial bus), data is transmitted pulse by pulse over a twisted pair (two wires), and in a parallel bus (parallel bus), data travels along several wires at the same time.
With greater performance, the parallel bus complicates the wiring of the car. The serial bus transmits information up to 1 Mbps.
Different blocks share data, the rule by which this happens is called a protocol. The protocol can send commands to different blocks, request data from one or all. In addition to a specific call to the device, the protocol can also set the importance of commands. For example, a command to turn on the engine cooling fan will have priority over a command to lower the side window.
The minimization of modern electronics made it possible to launch the production of cheap control modules and communication systems. In the automotive network, they can be combined into chains, stars and rings.
Information goes in both directions, for example, by turning on the high beam lamp, a signal will light up on the instrument panel - whether it shines or not.
The engine management system selects the best mode by receiving input from all devices in the circuit, the lighting system will turn the headlights on or off, the navigation system will plot or change the route, and so on.
Thanks to this protocol, the diagnosis of the engine and other car devices has been simplified.
The desire to have only one wire in the car did not come true, but the CAN module and data transfer protocol increased the reliability of the system and simplified the wiring.
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CAN bus - what is it?
CAN - bus ("can bus") is a control system for all electrical devices and digital communication in a car, which can receive information from devices, exchange data between them, and control them. Data on the technical condition and control signals go in digital form over twisted pair thanks to a special protocol. Power is supplied from the vehicle's on-board network to each consumer, but they are all connected in parallel. This option increased the reliability of the entire electrical circuit, reduced the number of wires and simplified installation.
What is CAN bus.
The history of the emergence of CAN began in the mid-80s of the last century. Bosch has partnered with Intel to develop a new digital data interface, the Controller Area Network (CAN).
Analog alarm connection (without CAN bus)
Why do you need a CAN bus in a car.
The CAN bus allows you to interconnect any number of sensors, controllers, actuators and other units located in the car (for example: ABS, SRS AIRBAG, ESP systems, immobilizer, engine control unit, climate, gearbox, central locking, light, suspension, instrument panel, etc...) in duplex mode (receiving and transmitting data) at speeds up to 1 Mbps. At the same time, the can bus itself consists of only two wires (twisted pair). Previously, hundreds of wires had to be used to connect blocks. the transfer of a unit of information from block to block was carried out via a separate wire.
Alarm setting via CAN bus
Car alarms with CAN module.
CAN module
Modern car alarms are produced with an integrated CAN module, which allows you to connect a car alarm directly to the car's digital CAN bus. The car alarm receives digital information about the status of limit switches, locks, ignition, handbrake, tachometer, etc. and can also control door locks, power windows, sunroof, standard alarms and some other car systems. allows you to significantly reduce interference with the standard wiring (connections are made to only 6-8 wires, instead of 15-20 in the variant without using a can bus) and avoids problems with the warranty on the car's electrical equipment.
On-board electronics systems in modern cars and trucks have a huge number of additional devices and actuators. In order for the exchange of information between all devices to be as efficient as possible, a reliable communication network must be in the car. In the early 80s of the 20th century, Bosch and the developer Intel proposed a new network interface - the Controller Area Network, which is popularly called the Can-bus.
1 About the principle of operation of the CAN bus network interface
Kan-bus in the car is designed to ensure the connection of any electronic devices that are capable of transmitting and receiving certain information. Thus, data on the technical condition of systems and control signals pass through the twisted pair cable in digital format. Such a scheme made it possible to reduce the negative impact of external electromagnetic fields and significantly increase the data transfer rate according to the protocol (the rules by which control units of various systems are able to exchange information).
In addition, the various do-it-yourself car systems has become easier. Due to the use of such a system as part of the vehicle's on-board network, a certain number of conductors were released that are capable of providing communication using various protocols, for example, between the engine control unit and diagnostic equipment, an alarm system. It is the presence of the Kan-bus in the car that allows the owner to identify controller malfunctions and errors with the help of special diagnostic equipment with his own hands.
CAN bus–this is a special network through which data is transmitted and exchanged between various control nodes. Each of the nodes consists of a microprocessor (CPU) and a CAN controller, which implements the executable protocol and ensures interaction with the vehicle network. The Kan bus has at least two pairs of wires - CAN_L and CAN_H, through which signals are transmitted through transceivers - transceivers capable of amplifying the signal from network control devices. In addition, transceivers perform such functions as:
- adjusting the data rate by increasing or decreasing the current supply;
- current limiting to prevent damage to the sensor or shorting of transmission lines;
- thermal protection.
To date, two types of transceivers are recognized - High Speed and Fault Tolerant. The first type is the most common and complies with the standard (ISO 11898-2), it allows you to transfer data at speeds up to 1MB per second. The second type of transceivers allows you to create an energy-saving network, with a transfer rate of up to 120 Kb / s, while such transmitters are not sensitive to any damage on the bus itself.
2 Network Features
It should be understood that data is transmitted over the CAN network in the form of frames. The most important of these are the identifier field (Identifire) and the data system (Data). The most commonly used type of message on the CAN bus is the Data Frame. This type of data transfer consists of the so-called arbitration field and determines the priority data transfer in the event that several system nodes transmit data to the CAN bus at once.
Each of the control devices connected to the bus has its own input impedance, and the total load is calculated from the sum of all executable blocks connected to the bus. On average, the input impedance of engine control systems that are connected to the CAN bus is 68-70 ohms, and the resistance of the information-command system can be up to 3-4 ohms.
3 Channel interface and system diagnostics
CAN control systems not only have different load resistances, but also different message rates. This fact complicates the processing of messages of the same type within the onboard network. To simplify diagnostics on modern cars, a gateway (resistance converter) is used, which is either made as a separate control unit or built into the car's engine ECU.
Such a converter is also designed to input or output certain diagnostic information via the "K"-line wire, which is connected during diagnostics or changes in network operation parameters either to the diagnostic connector or directly to the converter.
It is important to note that there are currently no specific standards for Can network connectors. Therefore, each of the protocols defines its own type of connectors on the CAN bus, depending on the load and other parameters.
Thus, when carrying out diagnostic work with your own hands, a unified OBD1 or OBD2 type connector is used, which can be found on most modern foreign and domestic cars. However, some car models, such as Volkswagen Golf 5V, Audi S4, do not have a gateway. In addition, the scheme of control units and CAN bus is individual for each make and model of car. In order to diagnose the CAN system with your own hands, special equipment is used, which consists of an oscilloscope, a CAN analyzer and a digital multimeter.
Troubleshooting work begins with removing the mains voltage (removing the negative terminal of the battery). Next, the change in resistance between the bus wires is determined. The most common types of Kan-bus malfunction in a car are a short or open line, failure of load resistors and a decrease in the level of message transmission between network elements. In some cases, without using the Can analyzer, it is not possible to detect a malfunction.
Modern machines use electronic control units (ECU, ECU - Electronic Control Unit) to control and control various machine systems, such as hydraulics, gearbox and engine.
Just as computers can be networked together, control units in a car can also be connected.
Benefits of a network connection:
- More sensitive control system
- Getting more complete and reliable data
- Fault detection and settings management is performed by means of software.
For example, an engine ECU can communicate with other machine ECUs through a network system CAN.
System CAN:Controller Area Network- a network of controllers. CAN was developed by Robert Bosch GmbH in the mid-1980s and is currently widely used in the automotive, aviation, tractor and other industries.
The CAN electronic communication system, which connects all machine control units to a network with a common cable (bus) and consists of one pair of wires, is called the CAN bus. The encoded data is sent from the control units to the CAN bus.
Drawing - CAN bus of 4 control units.
Shown above is a CAN bus consisting of 4 control units. Termination resistances (terminators, resistors) are installed at the ends of a common cable (bus). Typically, the resistance of each resistor is 120 ohms. The use of terminating resistors at the ends of the system avoids signal reflection at the end of the line, thereby ensuring the normal operation of the entire CAN network.
Signal transmission in the CAN bus is carried out by means of two wires twisted together (twisted pair, Twisted Pair). The use of a twisted pair of wires is due to differential data transmission and high protection of such a solution from external interference.
In our case, block #2 sends one signal over two twisted wires to the CAN bus, and this signal will have a different voltage on each twisted pair wire. Other blocks in the network read the signal and determine which block it is intended for and what command to execute (Blocks #1 and #4)
The transmission of the same signal to two wires (CAN High and CAN low) with different voltages is carried out using the "differential data transmission" method. At rest, the voltage on the CAN High and CAN low wires is 2.5 V. This state is called "recessive" and simply corresponds to the value of the "0" bit. CAN High wire will increase by at least 1 V to 3.5 V, and CAN low will also go down by 1 V to 1.5 V. In order to "understand" the voltage difference between CAN High and CAN low, each control unit is connected to the CAN bus via a transceiver, where the voltage difference U CAN Hi and U CAN Lo is converted into the final voltage U DIFF . The difference between CAN High and CAN low will be 2V and will be read by the receiving control units as a bit value of "1". This "differential transmission" of the signal eliminates the influence of the base voltage of 2.5 V and other voltage surges due to various interferences on the operation of control units. For example, there is a voltage drop in the on-board network by 1.5 V due to the inclusion of a powerful consumer in the network: U CAN Hi and U CAN Lo at rest 2.5 -1.5 = 1 V (U DIFF = 1 - 1 = 0 - Value of bit "0") Difference, when transitioning to the dominant state U CAN Hi = 2.5 +1 -1.5 = 2 V; U CAN Lo \u003d 2.5 -1 -1.5 \u003d 0 V. Total U DIFF \u003d 2 - 0 \u003d 2 V (Bit value "1"), even such an unrealistic drawdown did not affect the operation.
Drawing - CAN line principle
This is how signals are transmitted over the CAN bus. These signals themselves are "frames" (messages) that are received by all elements of the CAN network. The payload in a frame consists of an identification field (identifier) of 11 bits (standard format) or 29 bits (extended format, a superset of the previous one) and a data field of 0 to 8 bytes in length. The identification field tells about the contents of the packet and is used to determine the priority when trying to transmit simultaneously by several network nodes. Also in the frame (message) in addition to useful information contains service information. It is represented by validation fields, a revocation field, and other fields. At the end of the frame contains the "end of message field"
In the CAN bus, messages from control units must be transmitted to a common bus, then to avoid conflicts between blocks, each node checks the network for transmission of the dominant bit before sending the frame. The device transmitting the dominant bit is considered a priority. Thus, the device will wait for the release of the CAN line. On the one hand, such an algorithm of operation increases speed, but on the other hand, if one of the control units does not work correctly, the CAN bus may be completely “loaded” and it will be impossible to send a message to other units, elements of the CAN network (The line for them will always be busy).
Drawing - Message Structure
Finally, an example of work:
By switching the button, we initiate the command of the control unit No. 1 to send messages to the CAN bus. Unit 2 receives the message and decrypts in the message that the frame came for it with a command to turn on the light. Onboard voltage is supplied to the consumer.
Drawing -The principle of communication through CAN
This is the principle of the CAN bus without specific recesses. It is also worth noting that the CAN bus may have its own characteristics, depending on the application and the manufacturer. In the article, I talked about the most common CAN bus, which can be found in modern trucks and cars, tractors and various special equipment.
