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

1

A Zero Defeats a 1 Lower identifiers have Priority on the Bus. CAN is a Multiple Access Collision Avoidance (MACA) Net

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 messagePropagation: To allow time for this bit of data to propagate throughout the networkPhase 1: First part of the dataPhase 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

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1 BIT PAGE SELECT (0)

8 BIT PDU FORMAT

8 BIT PDU SPECIFIC

8 BIT USER DEFINED

8 BYTES OF DATA

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 degreesdivided by the number of cylinders.Data Length: 2 bytesResolution: 0.125 rpm/bit gain, 0 rpm offset (upper byte resolution = 32 rpm/bit)Data Range: 0 to 8031.875 rpmType: MeasuredSuspect Parameter Number: 190Reference: 5.3.7

PDU FORMAT & SPECIFIC = FF04 ELECTRONIC ENGINE CONTROLLER #1

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