The Controller Area Network (CAN) has become a de facto standard for automotive communications and it’s also having considerable impact in other industries where noise immunity and fault tolerance are more important than raw speed.
CAN is a multi-master serial bus standard for connecting Electronic Control Units (ECUs) also known as nodes. For technologically forward industries that need their embedded systems talking to each other, CAN hardware has beome an overwhelming choice because it’s relatively inexpensive and can be integrated into so many microcontrollers.
Taking a closer look at the architecture, two or more nodes are required on the CAN network to communicate. The complexity of the node can range from a simple I/O device up to an embedded computer with a CAN interface and sophisticated software. The node may also be a gateway allowing a standard computer to communicate over a USB or Ethernet port to the devices on a CAN network.
All nodes are connected to each other through a two wire bus. The wires are a twisted pair with a 120 Ω (nominal) characteristic impedance.
ISO 11898-2, also called high speed CAN, uses a linear bus terminated at each end with 120 Ω resistors
High speed CAN signaling drives the CAN high wire towards 5 V and the CAN low wire towards 0 V when transmitting a dominant (0), and does not drive either wire when transmitting a recessive (1). The dominant differential voltage is a nominal 2 V. The termination resistor passively returns the two wires to a nominal differential voltage of 0 V. The dominant common mode voltage must be within 1.5 to 3.5 V of common and the recessive common mode voltage must be within +/-12 of common.
There’s also a low speed or fault tolerant CAN (ISO 11898-3), which uses a linear bus, star bus or multiple star buses connected by a linear bus and is terminated at each node by a fraction of the overall termination resistance. The overall termination resistance should be about 100 Ω, but not less than 100 Ω.
With both high speed and low speed CAN, the speed of the transition is faster when a recessive to dominant transition occurs since the CAN wires are being actively driven. The speed of the dominant to recessive transition depends primarily on the length of the CAN network and the capacitance of the wire used.
Controller Area Network Training
Tonex offers a 2-day Controller Area Network Training course that covers a lot of useful, informational topics including:
- Principles of Controller Area Network
- Technical introduction to serial bus systems
- Controller Area Network (CAN) implementation in Embedded Systems
- J1939/71 Recommended Practice for Vehicle Application Layer
- Bus access methods, framing, bit timing, bit stuffing
- Controller Area Network Bus J1939 Data Acquisition Methods
- Automotive Networks and CAN Bus topology
- Principals of CSMA/CD and CSMA/CA
Who Should Attend
This course is designed for a wide cross section of professionals such as design and test engineers, programmers and technicians, verification and valuation engineers, embedded hardware and software engineers and project managers.
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