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Chapter 16
CAN Controller
User’s Manual U16504EE1V1UD00
16.1 CAN Protocol
CAN is an abbreviation of "Controller Area Network", and is a class C high speed multiplexed communi-
cation protocol. CAN is specified by Bosch in the CAN specification 2.0 from September 1991 and is
standardized in ISO-11898 (International Organization for Standardization) and SAE (Society of Auto-
motive Engineers).
16.1.1 Protocol Mode Function
(1)
Standard format mode
This mode supports an 11-bit message identifier thus making it possible to differentiate
between 2048 types of messages.
(2)
Extended format mode
In the extended format mode, the identifier has 29 bits. It is built by the standard identifier
(11 bits) and an extended identifier (18 bits).
When the IDE bits of the arbitration field is "recessive", the frame is sent in the extended format
mode.
When a message in extended format mode and a remote frame in standard format mode are
simultaneously transmitted, the node transmitting the message with the standard mode wins
the arbitration.
(3)
Bus values
The bus can have one of two complementary logical values: "dominant" or "recessive". During
simultaneous transmission of "dominant" and "recessive" bits, the resulting bus value will be
"dominant" (non destructive arbitration).
For example, in case of a wired-AND implementation of the bus, the "dominant" level would be
represented by a logical "0" and the "recessive" level by a logical “1”.
This specific representation is used in this manual.
Physical states (e.g. electrical voltage, light) that represent the logical levels are not given in this
document.
16.1.2 Message Format
The CAN protocol message supports different types of frames. The types of frames are listed below:
Data frame:
Carries the data from a transmitter to the receiver.
Remote frame:
Transmission demand frame from the requesting node.
Error frame:
Frame sent on error detection.
Overload frame:
Frame sent when a data or remote frame would be overwritten by the next
one before the receiving node could process it. The reception side did not
finish its operations on the reception of the previously received frame yet.