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Controller Area Network (CAN) is a multicast shared serial bus standard, originally developed in the 1980s by Robert Bosch GmbH, for connecting electronic control units (ECUs). CAN was specifically designed to be robust in noisy environments and can utilize a differential balanced line like RS-485. It can be even more robust against noise if twisted pair wire is used. Although initially created for automotive purposes (as a vehicle bus), nowadays it is used in many embedded control applications (e.g., industrial) that may be subject to noise. Multicast is the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once and only create copies when the links to the destinations split. ...
A male DE-9 serial port on the rear panel of a PC. In computing, a serial port is an interface on a computer system with which information is transferred in or out one bit at a time (contrast parallel port). ...
In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers. ...
Jump to: navigation, search // Events and trends The 1980s marked an abrupt shift towards more conservative lifestyles after the momentous cultural revolutions which took place in the 1960s and 1970s and the definition of the AIDS virus in 1981. ...
This article needs to be cleaned up to conform to a higher standard of quality. ...
In automotive electronics, an electronic control unit (ECU) is an embedded microcomputer that controls one or more of the electrical subsystems in a vehicle. ...
In science, and especially in physics and telecommunication, noise is fluctuations in and the addition of external factors to the stream of target information (signal) being received at a detector. ...
High-voltage differential (HVD) signalling is an electrical signalling system using high-voltage signals, as opposed to low-voltage differential signalling (see LVDS). ...
In telecommunication, a balanced line is a transmission line consisting of two conductors in the presence of ground, capable of being operated in such a way that when the voltages of the two conductors at all transverse planes are equal in magnitude and opposite in polarity with respect to ground...
EIA-485 (formerly RS-485 or RS485) is an electrical specification of a two-wire, half-duplex, multipoint serial connection. ...
25 Pair Color Code Chart 10BASE-T UTP Cable Twisted pair cabling is a common form of wiring in which two conductors are wound around each other for the purposes of cancelling out electromagnetic interference known as crosstalk. ...
Jump to: navigation, search A vehicle bus is an electronic communications network that interconnects components inside an automobile, bus, industrial or agrigultural vehicle, ship, or aircraft. ...
Bit rates up to 1 Mbit/s are possible at networks length below 40 m. Decreasing the bit rate allows longer network distances (e.g. 250 kbit/s at 250 m). In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ...
A megabit per second (Mbps or Mbit/s) is a unit of data transmission equal to 1,000 kilobits per second or 1,000,000 bits per second. ...
The metre, or meter (symbol: m) is the SI base unit of length. ...
A kilobit per second (kbps or kbit/s) is a unit of data transmission equal to 1,000 bits per second. ...
The CAN data link layer protocol is standardized in ISO 11898-1 (2003). This standard describes mainly the data link layer — composed of the logical link control (LLC) sublayer and the Media Access Control (MAC) sublayer — and some aspects of the physical layer of the ISO/OSI Reference Model. All the other protocol layers are left to the network designer's choice. The data link layer is layer two of the seven-layer OSI model. ...
Logical Link Control (LLC) is the upper portion of the data link layer of a local area network, as defined in IEEE 802. ...
In telecommunication, the term sublayer has the following meanings: In a layered open communications system, a specified subset of the services, functions, and protocols included in a given layer. ...
media access control is where people try to access a control to the media. ...
In telecommunication, the term sublayer has the following meanings: In a layered open communications system, a specified subset of the services, functions, and protocols included in a given layer. ...
The physical layer is level one in the seven level OSI model of computer networking. ...
The Open Systems Interconnection Reference Model (OSI Model or OSI Reference Model for short) is a layered abstract description for communications and computer network protocol design, developed as part of the Open Systems Interconnect initiative. ...
Data transmission
CAN transmits data through a binary model of "dominant" bits and "recessive" bits where dominant is a logical 0 and recessive is a logical 1. If one node transmits a dominant bit and another node transmits a recessive bit then the dominant bit "wins" (a logical AND between the two). AND Logic Gate In mathematics, logical conjunction (usual symbol and) is a logical operator that results in true if both of the operands are true. ...
| Truth tables for dominant/recessive and logical AND | | Bus state with two nodes transmitting | dominant | recessive | | dominant | dominant | dominant | | recessive | dominant | recessive | | Logical AND | So, if you are transmitting a recessive bit, and someone sends a dominant bit, you see a dominant bit, and you know there was a collision. (All other collisions are invisible.) The way this works is that a dominant bit is asserted by creating a voltage across the wires while a recessive bit is simply not asserted on the bus. If anyone sets a voltage difference, everyone sees it, hence, dominant. Truth tables are a type of mathematical table used in logic to determine whether an expression is true or whether an argument is valid. ...
Commonly when used with a differential bus, a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) scheme is implemented: if two or more devices start transmitting at the same time, there is a priority based arbitration scheme to decide which one will be granted permission to continue transmitting. In computer networking, Carrier Sense Multiple Access With Collision Avoidance (CSMA/CA) is a network control protocol in which: a carrier sensing scheme is used, a data station that intends to transmit sends a jam signal after waiting a sufficient time for all stations to receive the jam signal, the...
During arbitration, each transmitting node monitors the bus state and compares the received bit with the transmitted bit. If a dominant bit is received when a recessive bit is transmitted then the node stops transmitting (i.e., it lost arbitration). Arbitration is performed during the transmition of the identifier field. Each node starting to transmit at the same time sends an ID with dominant as binary 0, starting from the high bit. As soon as their ID is a larger number (lower priority) they'll be sending 1 (recessive) and see 0 (dominant), so they back off. At the end of ID transmission, all nodes bar one have backed off, and the highest priority message gets through unimpeded.
Frames All frames (aka messages) begin with a start-of-frame (SOF) bit that, obviously, denotes the start of the frame transmission.
CAN has four frame types:
- Data frame: a frame containing node data for transmission
- Remote frame: a frame requesting the transmission of a specific identifier
- Error frame: a frame transmitted by any node detecting an error
- Overload frame: a frame to inject a delay between data and/or remote frames
Data frame The data frame is the only frame for actual data transmission. There are two message formats: - Base frame format: with 11 identifier bits
- Extended frame format: with 29 identifier bits
The CAN standard requires the implementation must accept the base frame format and may accept the extended frame format. But must tolerate the extended frame format.
Base frame format The frame format is as follows: | Field name | Length (bits) | Purpose | | Start-of-frame | 1 | Denotes the start of frame transmission | | Identifier | 11 | A (unique) identifier for the data | | Remote transmission request (RTR) | 1 | Must be dominant | | Identifier extension bit (IDE) | 1 | Must be dominant | | Reserved bit (r0) | 1 | Reserved | | Data length code (DLC) | 4 | Number of bytes of data (0-8 bytes) | | Data field | 0-8 bytes | Data to be transmitted (length dictated by DLC field) | | CRC | 15 | Cyclic redundancy check | | CRC delimiter | 1 | Must be recessive | | ACK slot | 1 | Transmitter sends recessive and any receiver can assert a dominant | | ACK delimiter | 1 | Must be recessive | | End-of-frame (EOF) | 7 | Must be recessive | One restriction placed on the identifier is that the first 7 bits cannot be all recessive bits. A cyclic redundancy check (CRC) is a type of hash function used to produce a checksum, which is a small number of bits, from a large block of data, such as a packet of network traffic or a block of a computer file, in order to detect errors in transmission...
Extended frame format The frame format is as follows: | Field name | Length (bits) | Purpose | | Start-of-frame | 1 | Denotes the start of frame transmission | | Identifier A | 11 | First part of the (unique) identifier for the data | | Substitute remote request (SRR) | 1 | Must be recessive | | Identifier extension bit (IDE) | 1 | Must be recessive | | Identifier B | 18 | Second part of the (unique) identifier for the data | | Remote transmission request (RTR) | 1 | Must be dominant | | Reserved bits (r1 & r0) | 2 | Reserved | | Data length code (DLC) | 4 | Number of bytes of data (0-8 bytes) | | Data field | 0-8 bytes | Data to be transmitted (length dictated by DLC field) | | CRC | 15 | Cyclic redundancy check | | CRC delimiter | 1 | Must be recessive | | ACK slot | 1 | Transmitter sends recessive and any receiver can assert a dominant | | ACK delimiter | 1 | Must be recessive | | End-of-frame (EOF) | 7 | Must be recessive | The two identifier fields (A & B) combined form a 29-bit identifier. A cyclic redundancy check (CRC) is a type of hash function used to produce a checksum, which is a small number of bits, from a large block of data, such as a packet of network traffic or a block of a computer file, in order to detect errors in transmission...
Remote frame The remote frame is identical to the data frame except: - the RTR bit set to recessive
- data length contains the number of bytes that are required from the data frame
Error frame There are two types of error frames - Active Error Frame
- Transmitted by a node detecting an error on the network that is in error state "error active".
- Passive Error Frame
- Transmitted by a node detecting an active error frame on the network that is in error state "error passive".
Overload frame
Bit stuffing In CAN frames a bit of opposite polarity is inserted after five consecutive bits of the same polarity. This practice is called bit stuffing, and is due to the "Non Return to Zero" (NRZ) coding adopted. The "stuffed" data frames are destuffed by the receiver. Since bit stuffing is used, six consecutive bits of the same type (111111 or 000000) are considered an error. Bit stuffing implies that sent data frames could be larger than one would expect by simply enumerating the bits shown in the tables above. In telecommunication, bit stuffing is the insertion of noninformation bits into data. ...
Contrast with: return-to-zero. ...
ISO standards There are several CAN physical layer standards: The physical layer is level one in the seven level OSI model of computer networking. ...
- ISO 11898-2: CAN high-speed
- ISO 11898-3: CAN fault-tolerant (low-speed)
- ISO 11992-1: CAN fault-tolerant for truck/trailer communication
- SAE J2411: Single-wire CAN (SWC)
ISO 11898-2 uses a two-wire balanced signaling scheme. It is the most used physical layer in car powertrain applications and industrial control networks. In telecommunication, a balanced line is a transmission line consisting of two conductors in the presence of ground, capable of being operated in such a way that when the voltages of the two conductors at all transverse planes are equal in magnitude and opposite in polarity with respect to ground...
The ISO 11898-4 standard defines the time-triggered communication on CAN (TTCAN). It is based on the CAN data link layer protocol providing a system clock for the scheduling of messages.
Application layer implementations As the CAN standard does not include tasks of application layer protocols, such as flow control, device addressing, and transportation of data blocks larger than one message, many implementations of higher layer protocols were created. Among these are DeviceNet, CANopen, SDS, J1939 and CAN Kingdom. The flow control mechanism is used for controlling the flow of data in a network under well-defined conditions, while congestion control is used for controlling the flow of data when congestion has actually occurred [1]. Flow control mechanisms are classified by whether or not they have feedback. ...
SAE J1939 is the Vehicle Network Communication standard used for communication and diagnostics by heavy duty truck industry, predominantly in the United States. ...
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