Transcript Slide 1
Control Area Network CAN Developed by Bosch in 1983 as an automotive protocol, it was adopted by the Society of Automotive Engineers (SAE) in 1986. As a published open standard it has been widely adopted by industry. Many processors support CAN networking.. 0 A Zero Defeats a 1 Lower identifiers have Priority on the Bus. CAN is a Multiple Access Collision Avoidance (MACA) Net 1 The CAN Identifier (29 or 11 bits) identifies the Information – NOT the transmitter or receiver. Nodes transmit data on to the BUS, giving different data items different Ids. Nodes can read any or all of the data on the BUS. CAN is a BROADCAST media A receiver uses its internal MASK and IDENTIFIER registers to selectively capture information on the BUS If a MASK bit is set to a '1' then that bit in the incoming message must the same as the pre-set entry in the same bit location in the IDENTIFIER register. Each CAN data bit is broken down into 4 parts Sync Prop Phase 1 Phase 2 Synchronisation: To allow all receivers to synchronise their clocks to a new message Propagation: To allow time for this bit of data to propagate throughout the network Phase 1: First part of the data Phase 2: Second part of the data. The data is sampled between Phase 1 & Phase 2 QUESTION – If the processor has a 12 MHz System Clock what time parameters would you set up for each part of the bit to achieve a data rate of 250 Khz? SOCIETY OF AUTOMOTIVE ENGINEERS J1939 3 BITS PRIORITY 0 1 BIT PAGE SELECT (0) 8 BIT PDU FORMAT 8 BIT PDU SPECIFIC 8 BIT USER DEFINED 8 BYTES OF DATA PDU FORMAT & SPECIFIC = FF04 ELECTRONIC ENGINE CONTROLLER #1 BYTES 4 & 5 ENGINE SPEED Better known a RPM or Revolutions Per Minute. This is an integer variable defined in section 5.2.1.9 of the specification. 5.2.1.9 Engine Speed Actual engine speed which is calculated over a minimum crankshaft angle of 720 degrees divided by the number of cylinders. Data Length: 2 bytes Resolution: 0.125 rpm/bit gain, 0 rpm offset (upper byte resolution = 32 rpm/bit) Data Range: 0 to 8031.875 rpm Type: Measured Suspect Parameter Number: 190 Reference: 5.3.7 UNITS – RESOLUTION – OFFSET – RANGE Device Net COMMUNICATION OBJECT IDENTIFIER or COB-ID Service Data Objects or SDO Process Data Objects or PDO SDOs are used to read or write to/from the contents of a device object dictionary The real-time transfer of data between peers is achieved by means of PDOs An SDO Is used to access a node’ setup. Configuration and data. SDOs have the following format COMMAND,INDEX,SUB-INDEX,DATA The command is 1 byte The index uses 2 bytes The sub-index uses 1 byte The data field uses 4 bytes Other Wired Protocols – LINBUS Data Length 2/4/8 bytes determined by length control Other Wired Protocols – LINBUS have defined a full LIN frame Description: Description: lin frame An interesting feature