Chapter8 CAN

Chapter8 CAN - Controller Area Network (CAN) CAN is a...

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Controller Area Network (CAN) CAN is a real-time, serial-communication, multi-master vehicle network CAN specification defines the Data Link Layer , Developed by Robert Bosch, Gmbh (Germany) in 1986 to provide high-speed, robust communications in automotive applications (between three ECUs (electronic control units) in vehicles by Mercedes. UART was limited to point-to-point communication. They needed need a multi-master communication system. First CAN silicon fabricated in 1987 by Intel 1 st release CAN 1.2, current standard CAN 2.0 (1991) Automotive applications: low speed CANbus to operate window and seat controls. high speed CANbus for engine management or brake control. other applications: engine sensors, anti-skid systems, etc.
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CAN and related standards CAN Bus Specification Version 2.0 (data link layer) ISO/DIS 11898 (physical layer) Low speed Class A bus (<10 kbps) Class B bus (10 kbps – 125 kbps) High speed bus (125 kbps – 1 Mbps) ISO/DIS 11898-1: Road vehicles -- Controller area network (CAN) -- Part 1: Data link layer and physical signaling ISO/DIS 11898-2: Road vehicles -- Controller area network (CAN) -- Part 2: High-speed medium access unit ISO/CD 11898-3: Road vehicles -- Controller area network (CAN) -- Part 3: Low-speed fault tolerant medium dependent interface ISO/CD 11898-4: Road vehicles -- Controller area network (CAN) -- Part 4: Time triggered communication
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Three types of CAN controllers: 2.0A controllers transmit and receive only Standard format messages # of unique identifiers available to users, on a single 2.0A network, is 2,032 (2 11 - 2 4 ). 2.0B passive controllers will receive Extended format messages but then ignore them. 2.0B controllers can send and receive messages in both formats. # of unique identifiers available on a 2.0B network is in excess of 500 million! 2.0B and 2.0B passive controllers can coexist on a network If 29 bit identifiers are used on a bus which contains 2.0A controllers, the bus will not work!!!
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CAN Bus physical level Physical layer is not part of the Bosch CAN standard CAN bus consists of two wires: CAN-High and CAN-Low. Differential mode decreases noise interference Voltage level in recessive state for idle bus Non return to zero (NRZ) signaling with “bit stuffing”: Recessive high and dominant low states
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ISO bus/transceiver standards ISO 11898 Twisted pair, shielded or unshielded. Impedance of the cable = 120 12 ohms Signal recessive state: CAN-high = 2.5v, CAN-low = 2.5v Signal dominant state: CAN-high = 3.5v, CAN-low = 1.5v for the recessive state, nominal voltage for the two wires is the same to decreases the power drawn from the nodes through the termination resistors. 120 ohm termination resistors on each end of the wires.
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Chapter8 CAN - Controller Area Network (CAN) CAN is a...

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