24-12-2012, 12:04 PM
CAN Bus Introduction
CAN Bus.pptx (Size: 400.97 KB / Downloads: 24)
CAN- Controller Area Network
CAN bus is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer.
Development started originally in 1983 by Robert Bosch.
Very reliable, robust and inexpensive, well proven technology.
Application
Modern automobile may have as many as 70 electronic control units for various subsystems.
transmission, airbags, antilock braking/ABS, audio systems, windows, doors, mirror adjustment, battery etc.
CAN bus provides interconnection between these.
The effect of CAN bus can be seen in the next slide.
Other Applications
Military vehicles
Medical systems
Agricultural machinery
Marine control and navigation
Elevator control systems
Industrial machinery
Technology
Each node sends and receives messages.
Message consists of an ID (identifier), representing priority of the message.
When bus is free, any node may begin to transmit. If two or more nodes begin sending messages at the same time, the message with the more dominant ID will overwrite other nodes' less dominant IDs.
Thus only the dominant message remains and is received by all nodes. This mechanism is priority based bus arbitration.
Data transmission
Protocol used by CAN- message that is transmitted with highest priority will succeed, and lower priority message will sense, back off and wait.
Dominant is a logical 0 and recessive is a logical 1
If one node transmits a dominant bit and another a recessive bit then the dominant bit "wins“. – logical AND
If a recessive bit is being transmitted while a dominant bit is sent, the dominant bit is displayed, evidence of a collision.
All other collisions are invisible.
Dominant bit is asserted by creating a voltage across the wires, recessive bit is not asserted on the bus.
If any node sets a voltage difference, all nodes will see it. Thus there is no delay to the higher priority messages.